Aerosol and Air Quality Research, 17: 3006–3036, 2017 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2017.03.0097

Chemical Characterization of Wintertime Aerosols over Islands and Mountains in East Asia: Impacts of the Continental Asian Outflow

Shantanu Kumar Pani1, Chung-Te Lee2*, Charles C.-K. Chou3, Kojiro Shimada4,5, Shiro Hatakeyama4,5, Akinori Takami6, Sheng-Hsiang Wang1, Neng-Huei Lin1,4**

1 Department of Atmospheric Sciences, National Central University, Taoyuan 32001, Taiwan 2 Graduate Institute of Environmental Engineering, National Central University, Taoyuan 32001, Taiwan 3 Research Center for Environmental Changes, Academia Sinica, Taipei 11529, Taiwan 4 Global Innovation Research Organization, Tokyo University of Agriculture and Technology, Tokyo 1083-8538, Japan 5 Institute of Agriculture, Graduate School of Tokyo University of Agriculture and Technology, Tokyo 1083-8538, Japan 6 Center for Regional Environmental Research, National Institute for Environmental Studies, Ibaraki 305-8506, Japan

ABSTRACT

This study aimed to characterize the wintertime surface aerosol chemistry over islands and mountains sites (i.e., Cape Fuguei, Mt. Bamboo, Mt. Lulin, Cape Hedo, and Kumamoto) in East Asia. Aerosols were sampled over a 24-h period as part of an intensive observational period (IOP) in winter 2015. Aerosol samples were analyzed for water-soluble inorganic –3 ions (WSIIs), organic carbon (OC), and elemental carbon (EC). PM2.5 mean concentration (in µg m ) was found the highest over Kumamoto (22 ± 7), followed by Cape Fuguei (20 ± 9), Cape Hedo (11 ± 5), Mt. Bamboo (10 ± 13), and Mt. Lulin (4 ± 3). Strong correlations (r > 0.91) in ion charge balance suggested the good quality of data-sets and the ions share 2– + common source origins. Larger variations in (non-sea-salt-sulfate) nss-SO4 and NH4 over all the sites indicated the significant contribution of anthropogenic emissions from continental Asian outflow. OC was found the most abundant resolved component in PM2.5 over Mt. Lulin (37.58 ± 25.90%) and Mt. Bamboo (33.24 ± 24.11%) than that over Cape Fuguei (11.94 ± 3.48%). OC3 (evolved at 280–480°C) was the most abundant in OC over all the sites, indicating the possible contributions of biomass-burning (BB) while EC1-OP (EC evolved at 580°C minus the pyrolized OC) was found the highest in EC over Cape Fuguei. Analysis of back-trajectories and fire-counts suggested the influence of long-range – transported BB from continental Asian outflow. Higher concentrations of PM2.5 along with the BB tracers (i.e., NO3 , OC3, and EC1-OP) were also observed during the influence of continental Asian outflow. This study provides needful information to understand the effect of continental Asian outflow on the air quality over East Asia. We propose the long- term and extensive field measurements to upgrade our knowledge on continental Asian outflow BB influence over islands and mountains in East Asia.

Keywords: Aerosol chemistry; Water soluble inorganic ions; Carbonaceous fractions; Anthropogenic; Biomass burning; Long range transport.

INTRODUCTION human health (IPCC, 2007). Arising from both natural (e.g., soil dust, sea-salt, botanical debris, volcanic dust, Atmospheric aerosols influence solar radiations (Charlson forest fires, and gas-to-particle conversion) and anthropogenic et al., 1992), cloud microphysics (Penner et al., 2001), (e.g., industrial processes, vehicular emissions, fossil-fuel precipitation efficiency and photochemistry of troposphere and open burning) sources (IPCC, 2001), aerosol plays a (IPCC, 2001), global climate (Charlson et al., 1992), and crucial role among their sources, transport, and deposition mechanisms of various pollutants in the atmosphere. Aerosol distribution is controlled by emissions, transport, transformation and loss processes in the atmosphere (Sahu * Corresponding author. et al., 2009). Aerosols can be transported from areas of Tel.: +886-3-422-7151 ext. 34657 high emissions to relatively clean remote sites regionally. E-mail address: [email protected] Atmospheric transport is the extensive pathway of various ** Corresponding author. chemical species from land to open ocean (Simoneit, 2002, Tel.: +886-3-422-7151 ext. 65531 2004) and remote locations (Lee et al., 2011). The chemical E-mail address: [email protected] characterization of atmospheric aerosols is vital to determine

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3007 their effects on climate and human health (Watson, 2002) also investigated within the Seven South East Asian Studies and also to understand their various source origins. (7-SEAS) framework (Lin et al., 2013). Plume signatures Emission inventories show large regional differences were also investigated above boundary layer over Hong mainly due to contributions from various sectors with Kong (Chan et al., 2003; Deng et al., 2008), at Mt. Lulin in different emissions factors in East Asia (Woo et al., 2003; central Taiwan (Sheu et al., 2010; Lee et al., 2011; Lin et Bond et al., 2004). A number of aerosol measurements al., 2014; Chuang et al., 2014), and possibly even near the have been made to investigate the aerosol transport and surface in the southern Taiwan (Tsai et al., 2013; Yen et transformation processes over the downwind regions of the al., 2013). East Asian continent (Sahu et al., 2009; Kundu et al., 2010a; Liu et al. (2003) analyzed the contributions from various Kunwar and Kawamura, 2014; Shimada et al., 2015; Zhu sources (i.e., fossil fuel, biofuel, and BB) to the Asian outflow et al., 2015; Shimada et al., 2016). The most systematic and over the West Pacific by modelling studies. Anthropogenic extensive measurements were made during the Transport and emissions of aerosol and trace gases from Asian outflows (i.e, Chemical Evolution over the Pacific (TRACE-P) campaign in central, northern and northeastern China) were investigated the spring of 2001 (Jacob et al., 2003) and the Aerosol over Jeju Island, Gosan, Korea in spring of 2005 (Sahu et Characterization Experiment (ACE)-Asia 2001 (Huebert et al., 2009). These outflow emissions from the Asian continent al., 2003). Rapid economic growth and urban development were associated with a high-pressure system centered over cause large scale anthropogenic emissions of aerosol and the northern region of China and Mongolia (Sahu et al., trace gases in East Asia (Streets and Waldhoff, 2000; Streets 2009). Seasonal variations of diacids, ketoacids, and α- et al., 2003). Apart from anthropogenic emissions, East dicarbonyls in long-range transported aerosols from Asian Asia is one of the most active biomass burning (BB) regions continent were investigated at Jeju Island, Korea during in the world with significant aerosol loadings (van der Werf et April 2003–April 2004 (Kundu et al., 2010a). Kundu et al. al., 2006). BB is a common energy source for cooking and (2010a) demonstrated that the Asian outflows from northeast space heating in East Asia (Verma et al., 2015). China most likely affect the air quality of Jeju Island and Regionally, the largest contributions of BB are from the surrounding ocean in western North Pacific Rim (NPR). boreal Asia (Russia), South East Asia (SEA; comprising Kunwar and Kawamura (2014) investigated the carbonaceous Vietnam, Laos, Combodia, Thailand, Myanmar, and west and nitrogenous components as well as major ions in aerosols Malaysia), China, and Mongolia (Streets et al., 2003; van from subtropical Okinawa Island, Japan and reported der Werf et al., 2006, 2010). Open BB (both forest fires important contribution from Asian dusts and anthropogenic and open burning of crop residues) is a dominant source in sources including BB, vehicular emissions and coal boreal Asia and SEA (Streets et al., 2003). Intensive BB combustions. Zhu et al. (2015) studied the wintertime maxima emissions frequently occur in the SEA during every spring of anhydrosugars in ambient aerosols from Okinawa Island and investigated elsewhere (Lin et al., 2013, 2014; Lee et and reported the effect of East Asian BB emissions on the al., 2016; Pani et al., 2016a, b; Khamkaew et al., 2016; air quality in the western NPR. BB organic tracers (i.e., Tsay et al., 2016 and references therein). Burning of grassland levoglucosan, mannosan, and galactosan) in Asian aerosols is dominant in Mongolia while burning of crop residues is transported downwind to the western NPR by westerly dominant in China (Streets et al., 2003). Large amounts of winds were investigated and studied over Chichijima Island in crop residues are burned in the field during the post- the western NPR (Verma et al., 2015). Similarly, Deshmukh harvest seasons (i.e., May–June and October–November) et al. (2016) extensively investigated the size distributions in eastern China (Streets et al., 2003; Yan et al., 2006). and formation processes of various water soluble diacids, The open BB could cause severe regional air pollution and carbon fractions and inorganic ions in spring aerosols at haze issue over Beijing–Tianjin–Hebei areas of China, the Okinawa Island, Japan and demonstrated the significant Pearl River delta, and the Yangtze River delta (Zhu et al., influence of anthropogenic and BB burning aerosols emitted 2010; Cheng et al., 2014 and references therein). Several from East Asia on the molecular compositions of water- studies reported significant impact of BB emissions on air soluble organic aerosols in the western NPR. quality over northern China and Mongolia in winter and The abovementioned studies investigated the chemical remarkably in Beijing (Wang et al., 2006; Yu et al., 2013; profile of ambient aerosols and identified some tracers to You et al., 2015 and references therein). Atmospheric understand the influence of long-range transported aerosols were greatly influenced by the burning of agriculture anthropogenic and BB emissions from Asian outflows over crop residue and fallen leaves in Northern China during NPR. Influence of BB emissions from Asian outflows were late September to early November (You et al., 2015). The identified and reported most significant in winter over the prevalence of dry weather since late autumn at most outflow region of East Asia (e.g., Korea and Japan) and regions of northern China (Zhai et al., 2005) increases the western NPR. However, the influence of BB emissions risks of forest and grassland fires (You et al., 2015). from Asian outflows on the aerosol chemical characteristics Emissions from such burning activities can affect regional over islands and mountains in East Asia (e.g., Taiwan) are air quality and climate through long distance transport not yet thoroughly investigated and well understood. Aerosol (Mochida et al., 2010; Zhu et al., 2015). Springtime regional chemical characterization is essential in identifying the transport of SEA BB downwind to southeastern China, source influence in the process of source apportionment. South China Sea (SCS), East Asia, western and central The main goal of this work is to characterize the signature Pacific Ocean, northeastern China, even over Japan were profiles of anthropogenic or BB emissions from continental

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Asian outflow, with reference to the composition of water al., 2010; Lee et al., 2011; Chuang et al., 2014). More soluble inorganic ions (WSIIs) and carbonaceous fractions detailed descriptions of the Mt. Lulin site are available in in wintertime aerosols collected over islands and mountains the literature (Sheu et al., 2010). in East Asia. Sampling of PM2.5 (cut sizes ≤ 2.5 µm) aerosols for chemical analysis was made continuously over Cape Fuguei MEASUREMENTS, DATA, AND METHODOLOGY (12 days; 25 October–3 November and 9–10 November, 2015), Mt. Bamboo (14 days; 28 October–10 November, Site Description, Aerosol Sampling, and Chemical 2015), and Mt. Lulin (14 days; 28 October–10 November, Analysis 2015). Ambient PM2.5 and PM2.5-10 (2.5 ≤ cut sizes ≤ 10 µm) Aerosol sampling was conducted at three distinct sites aerosol samples over Cape Fuguei were manually collected i.e., Cape Fuguei (25.29°N, 121.53°E, 10 meter above mean for 24 hours (08:00 a.m. to 08:00 a.m. local time) by using sea level (amsl)), Mt. Bamboo (25.18°N, 121.53°E, 1103 m a Dichotomous Sequential Air Sampler (R&P Partisol 2025; amsl), and Mt. Lulin (23.47°N, 120.87°E, 2862 m amsl) in Rupprecht & Patashnick, Co.). The mass concentrations of East Asia (Fig. 1) during the winter period (25 October–10 both PM2.5 and PM2.5-10 were weighted after appropriate November 2015; 17 days) as a part of an intensive conditioning for each samples and used for further observational period (IOP). Cape Fuguei is located on the chemical analysis. However, 24 hourly PM2.5 samples over northwestern tip of Taiwan and mainly covered with Mt. Bamboo (08:00 a.m. to 08:00 a.m. local time) and Mt. dwarfed and twisted local vegetation due to the constant Lulin (09:00 a.m. to 09:00 a.m. local time) were collected sea winds. Owing to its location, it is free from all types of by using collocated R&P ChemComb Model 3500 Speciation local activities for most of the time, particularly for northeast Sampling Cartridges (Thermo Fisher Scientific Co., Inc., monsoon prevailing period. Mt. Bamboo is located at an Waltham MA, USA) supported by tripods, as described in isolated peak inside the Yangmingshan National Park in Chuang et al. (2013b). After the sampling collections, the northern Taiwan and about 17 km away from the northern collected filters (both Teflon and quartz fibers) were stored Taiwan coastline. This site primarily receives the in refrigerator at 4°C to maintain their chemical stability, northeasterly monsoonal flow and frontal passages during and transported back to the laboratory in Taiwan for filter the winter months and frequently immersed in clouds. weighing, conditioning, and subsequent chemical analysis. Moreover this site is occasionally located above the Proper care was taken during collection and preservation of planetary boundary layer and the boundary layer dynamics the samples until the analysis. regulate the vertical transport of aerosols from the sea The Teflon® filters (R2PJ047 Teflo, PALL Life Sciences, surface to this site like the Yangmingshan mountain Inc., Ann Arbor, MI, USA) were weighed by using a Mettler (826 m amsl) site (Chou et al., 2017). A more detailed MX5 Microbalance (Mettler Toledo Co. Inc., Greifensee, description about Mt. Bamboo site can be found elsewhere Switzerland), with a sensitivity of ± 1 µg m–3 in a stable (Lin and Peng, 1999; Wang et al., 2010; Sheu and Lin, environment of 30 ± 5% for relative humidity and 23 ± 2°C 2011). Mt. Lulin is a high-elevation background station for temperature. Ion chromatograph (DX-120 for cations located inside the Jade Mountain National Park in Taiwan and DX-1000 for anions, Dionex Co., Inc., Sunnyvale, CA, and a part of the Central Mountain Range. This site is also USA) was used to analyze the WSIIs i.e., sodium (Na+), + + 2+ free from direct influence of local pollutions and lies in the ammonium (NH4 ), potassium (K ), magnesium (Mg ), 2+ – – free troposphere. Moreover, this is an ideal site to conduct calcium (Ca ), chloride (Cl ), nitrate (NO3 ), and sulfate 2– measurements of long-range transported air pollutants in (SO4 ), from the teflon filter samples. Calibration curves for the free troposphere in East Asia (Wai et al., 2008; Sheu et both anion and cation standards were checked intermittently

Fig. 1. Geographic locations of Cape Fuguei, Mt. Bamboo, Mt. Lulin, Cape Hedo, and Kumamoto in East Asia (adopted from Google Earth).

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3009 to ensure the correctness of the analyzed signals. More details Estimation of Sea-Salt and Non-Sea-Salt Components of the sampling procedure and analytical methods for Sea-salt particles contribute significantly to ambient WSIIs can be found elsewhere (Lee et al., 2011; Chuang et aerosols at the locations close to the sea (Park et al., 2016). + + + 2+ al., 2013a, b; Lee et al., 2016). Sea-salt emissions are comprised of Na , NH4 , K , Mg , 2+ – 2– The quartz filters (TISSUQUARTZ 2500QAT-UP, Ca , Cl , and SO4 (Ni et al., 2013). In order to analyze PALL Life Sciences, Inc., Ann Arbor, MI, USA) were the source origins (i.e., whether it is oceanic or continental) analyzed for carbonaceous contents (OC and EC) by using of the collected ions, sea-salt (ss) and non-sea-salt (nss) a carbon analyzer (DRI Model 2001A, Atmoslytic Inc., components were calculated using “Na+” as a reference Calabasas, CA, USA). The filter punch (0.5 cm2) was element. Mass concentration of nss components were analyzed for 8 carbonaceous fractions (OC1, OC2, OC3, estimated as follows (Ni et al., 2013) OC4, OP, EC1, EC2, and EC3) following the IMPROVE 2– 2– + (Interagency Monitoring of Protected Visual Environments) [nss-SO4 ] = [SO4 ] – 0.25 × [Na ] (1) protocol with the TOR (thermal optical reflectance) correction scheme (Chow et al., 1993; Chow et al., 2004; Watson et [nss-K+] = [K+] – 0.036 × [Na+] (2) al., 2005). Four OC fractions (OC1, OC2, OC3, and OC4) were determined at 140°C, 280°C, 480°C and 580°C, [nss-Ca2+] = [Ca2+] – 0.038 × [Na+] (3) respectively in a pure He atmosphere. EC1, EC2, and EC3 were determined at 580°C, 740°C, and 840°C, respectively [nss-Mg2+] = [Mg2+] – 0.118 × [Na+] (4) in a 2% O2/98% He atmosphere. The residence time of 2– + 2+ 2+ + each heating step was defined by the flattening of the carbon where [SO4 ], [K ], [Ca ], [Mg ], and [Na ] represents the 2– + 2+ 2+ signal. The pyrolyzed carbon fraction (OP) was determined mass concentrations of measured SO4 , K , Ca , Mg , and + –3 2– + 2+ when reflected laser light returns to its initial value after Na in µg m , respectively. [nss-SO4 ], [nss-K ], [nss-Ca ], oxygen is introduced. Generally, OC is defined as OC1 + and [nss-Mg2+] represents the mass concentrations of nss 2– + 2+ 2+ –3 OC2 + OC3 + OC4 + OP and EC is defined as EC1-OP + part of SO4 , K , Ca , and Mg , in µg m , respectively. 2– + 2+ 2+ + EC2 + EC3. The detection limit for the carbon analyzer The mass ratio of SO4 , K , Ca , and Mg to Na were was 0.05 µg C cm–2 for both OC and EC. The resolved EC 0.25, 0.036, 0.038, and 0.118, respectively (Ni et al., 2013). fractions were further classified into char-EC (EC1-OP) and soot-EC (EC2 + EC3) (Han et al., 2007; Chuang et al., Estimate of Secondary Organic Carbon and Organic 2013b) for source identifications. More details of the Matter sampling procedure and analytical methods for carbonaceous The EC-tracer method (e.g., Turpin and Huntzicker, fractions can be found elsewhere (Chuang et al., 2014; Lee 1991) was used to estimate the contributions of the primary et al., 2016). organic carbon (POC) and secondary organic carbon (SOC) In order to extend our knowledge about East Asian to total carbonaceous aerosols. EC and POC commonly aerosols, PM2.5 aerosols were also sampled over Cape Hedo, have the same source origins (Pavuluri et al., 2011); hence Okinawa Island, Japan (26.87°N, 128.25°E; 60 m amsl) the EC-tracer method assumes the relatively constant and Kumamoto, Kyushu Island, Japan (32.8°N, 130.7°E) OC/EC ratios for given area, season and local meteorology in East Asia during the same study period in addition to the (Kunwar and Kawamura, 2014). The minimum OC/EC aforementioned sites. PM2.5 sampling was made continuously ratio was used to estimate the SOC formation widespread over Cape Hedo (13 days; 26 October–07 November, 2015) (Turpin and Huntzicker, 1995; Pavuluri et al., 2011). In this and Kumamoto (7 days; 26–31 October, 2015). Detailed study, the concentrations of SOC and POC were estimated descriptions of these sites can be found elsewhere (Moreno by the following equations et al., 2013; Shimada et al., 2015; Misawa et al., 2017). In brief, Cape Hedo is situated at the northern end of Okinawa OC POC EC k (5) Island, about 100 km from Naha, the largest city on the EC island, and about 650 km from Shanghai, a major city in min mainland China. There are no such large residential or industrial areas near this site. Kumamoto sampling site is SOC = OCmeas – POC, (6) situated on the island of Kyushu in Western Japan (Moreno et al., 2013, Fig. 1) approximately midway between Tokyo where OCmeas is the measured OC concentration, (OC/EC)min (~1000 km in northeast direction) and Shanghai (~1000 km is the estimated minimum OC/EC ratio during the sampling southwest direction). This site is not impacted by any period, k is the parameter for non-combustion sources nearby heavy industrial point sources and is an excellent contributing to the POC that is assumed to be negligible. site for investigating the characteristics of transboundary The minimum OC/EC ratios in PM2.5 were 3, 1.1, and 2.3 aerosol intrusions (Moreno et al., 2013). 24 hourly PM2.5 over Cape Fuguei, Mt. Bamboo, and Mt. Lulin, respectively aerosols over Cape Hedo and Kumamoto were sampled (supplement Fig. S1). with six-stage cascade impactor (Model 3180, KANOMAX, All the aforementioned sampling sites in this study are Osaka, Japan) and analyzed only for WSIIs. More detailed free from local anthropogenic activities; located in the about the sampling and analysis procedures can be found Asian outflow region and receiving the long range transported elsewhere (Itahasi et al., 2017; Tatsuta et al., 2017). aerosols. Aerosols are subjected to aging processes during

3010 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 the atmospheric transport and result in more oxygenated and Mt. Lulin (14%). Cape Fuguei was influenced by the organic species (Kundu et al., 2010; Kunwar and Kawamura, Asian outflow through both Paths C and F, whereas Mt. 2014). Turpin and Lim (2001) reported that organic matter Bamboo and Mt. Lulin were only through Path F. Similar (OM) in the atmosphere estimated by the product of measured BT results were derived for investigation the origin of air OC concentration with a conversion factor of 1.6 ± 0.2 masses over the Dongsha Island (Pani et al., 2016c) in the (urban aerosols) and 2.1 ± 0.2 (aged aerosols). We used the northern SCS and Yangtze Delta region of China (Liu et conversion factor of 2.1 in this present study to estimate al., 2012). Zhu et al. (2015) reported the influence of 65– the OM concentrations. 70% of air masses originated in western to central Russia and passed through Mongolia and northern and northeastern Backward Air Mass Trajectories and Fire Counts China to Cape Hedo, while another 30–35% of air masses Trajectory is the time-integration of the change in originating from the northern and northeastern China with position of an air parcel as it is transported by the wind. shorter transport distances. Path G carries mostly marine Air mass trajectories were calculated in a backward mode aerosols to Mt. Bamboo (29%) and Mt. Lulin (29%) from (path of air movement arriving at a receptor location) by the western Pacific. Cape Hedo was also influenced by using the HYSPLIT-4 (Hybrid Single-Particle Lagrangian both oceanic (from western Pacific) and continental (from Integrated Trajectory – Version 4) model developed by Asian outflows) air masses (Kunwar and Kawamura, 2014) NOAA (National Oceanic and Atmospheric Administration, during autumn (September, October and November). USA) Air Resources Laboratory (http://www.arl.noaa.gov/ Strong influence of continental air masses was detected ready/hysplit4.html) during the study period (Draxler and over Cape Fuguei and Mt. Bamboo as compared to Mt. Lulin Rolph, 2003). The seven-day back-trajectories (BT) ending in this study. Cape Hedo receives the air masses exclusively at ground level of all the three aforementioned study sites originating from the Asian continent during autumn (Zhu at 00/06UTC daily for the measurement days were analyzed et al., 2015, Figs. 2(k)–2(l)) and winter (Zhu et al., 2015, in order to investigate the influence of continental Asian Figs. 2(a)–2(b)) with strongest influence of Asian outflow outflows (anthropogenic/BB) on ambient aerosols. A total dominated by the winter Asian monsoon. Air mass was number of BTs studied (NB) during the sampling period (1 frequently transported from the Asian continent to the BT daily) over Cape Fuguei, Mt. Bamboo, and Mt. Lulin Kumamoto during October (Misawa et al., 2017, Figs. 5(a)– were 12, 14, and 14, respectively and their relative frequency 5(b)). distributions (e.g., Pani and Verma, 2014; Verma et al., Vander Werf et al. (2006) reported a bimodal pattern 2014) were calculated. Burning activities in East Asia were with two maxima of BB emissions in spring and autumn in illustrated by fire-counts and were obtained from the central Asia (Mongolia, China, and Japan) on the basis of MODIS (Moderate Resolution Imaging Spectroradiometer) satellite observation and model simulation. Monthly value Terra satellite (http://disc.sci.gsfc.nasa.gov/neespi/data-hol of total fire-counts in middle-to-north Asia (30–60°N, 80– dings/mod14cm1.shtml). 130°E) showed a secondary peak (total counts 17838) in October (Zhu et al., 2015, Fig. S1 in the supplement). The RESULTS AND DISCUSSIONS dominant type of fire-counts was forest fires in Russia and part of the northeastern China, savanna in Mongolia and Air Mass Origins and Fire Counts Inner Mongolia in China, agricultural wastes in the northern Representative BT paths (Figs. 2(a)–2(c)), indicating the and northeastern China, and deforestation in South China influence of air masses originating from different source and Southeast Asia (Van der Werf et al., 2010). Ambient regions on ambient aerosols at Cape Fuguei, Mt. Bamboo, aerosols over Okinawa affected by both indoor and open- and Mt. Lulin sites. The details of possible pathways and field burning of woods and agricultural wastes in middle- their relative frequency (%) are presented in Table 1. BT to-north Asia during winter, open burning of wheat straw pathways to Cape Fuguei (NB: 12) and Mt. Bamboo (NB: in the northern China during spring and open burning of 14) were found very similar but distinct over Mt. Lulin maize straw in the northern and northeastern China during (NB: 14). Entrainment of air pollutants along each BT was autumn and forest-fires in the southern China and Southeast considered more alike. Originating from the Yellow Sea Asia (Zhu et al., 2015). On the basis of the BT paths and (YS) or East China Sea (ECS), the Path A carries mainly fire-counts analyzed, it could be summarized that aerosols marine aerosols to Cape Fuguei (33%), Mt. Bamboo (21%), over the sampling sites in the present study were influenced and Mt. Lulin (14%). Similarly, Path B influences Cape by the BB emissions from open burning of wheat and maize Fuguei and Mt. Lulin site with mostly marine aerosols. straw in the northern and northeastern China. Path C carries mostly continental Asian outflow to Cape Fuguei (42%) only. Path D carries both oceanic and Distribution of Aerosol Mass continental aerosols to Mt. Bamboo (29%) only and Path E The simultaneous measurement of PM2.5 concentrations carries mainly mixed aerosols only to Mt. Lulin (29%). BT obtained gravimetrically from Dichotomous Sequential Air pathways to Mt. Lulin during October to November indicated Sampler (R&P Partisol 2025) and from a semi-continuous that most of the trajectories traverse over a marine particulate monitor i.e., Tapered Element Oscillating atmosphere and the coastal areas of China and Korea (Wai Microbalance (TEOM 1405-DF, Thermo Scientific Inc.) et al., 2008, Fig. 3(c)). Path F mostly carries Asian outflow were strongly correlated (r = 0.99) over Cape Fuguei. For to all the sites i.e., Cape Fuguei (17%), Mt. Bamboo (21%), comparison purpose only, we used the PM2.5 mass from

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Fig. 2. Possible pathways based on 7-day BTs over (a) Cape Fuguei, (b) Mt. Bamboo, and (c) Mt. Lulin in East Asia. The blue dot and its size denote the annual CO emission based on Streets et al. (2003). Also shown are the gridded fire-counts during October–November, 2015 from the MODIS Terra satellite (http://disc.sci.gsfc.nasa.gov/neespi/data-holdings/mo d14cm1.shtml). The paths with occurrence % of BT ending at each location are denoted, as described in Table 1. For the interpretation of references to the color for BT paths in Figs. 2(a)–2(c), the reader can refer to the web version of this article.

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Table 1. Details of possible pathways based on 7-day BTs and their relative frequency (%) over Cape Fuguei, Mt. Bamboo, and Mt. Lulin. Relative frequency (in %) Paths Description of possible pathways of BT Cape Fuguei Mt. Bamboo Mt. Lulin (NB = 12) (NB = 14) (NB = 14) Originating from Yellow Sea (YS) or East China Sea Path: A (ECS) traversed over a marine atmosphere and the 33 (n = 4) 21 (n = 3) 14 (n = 2) coastal areas of China and Korea Path: B Originating locally in the vicinity of the ECS 8 (n = 1) 0 (n = 0) 14 (n =2) Originating from mainland China, while travel mainly Path: C* 42 (n = 5) 0 (n = 0) 0 (n = 0) along the Chinese coast but over a short distance Originating from Taiwan strait but come along Path: D 0 (n = 0) 29 (n = 4) 0 (n = 0) southeastern coastal China Originating from the coastal area of Korea and passed Path: E 0 (n = 0) 0 (n = 0) 29 (n = 4) over ECS; Originating from elevated regions over the northern and northeastern China and Mongolia and covered the Path: F* 17 (n = 2) 21 (n = 3) 14 (n = 2) longest distance through the coastal areas of China and on the way along the ECS Path: G Originating mainly from the western Pacific 0 (n = 0)** 29 (n = 4) 29 (n = 4) NB: number of BT analyzed; n: number of days the respective path was seen during the sampling period. * Paths represent the continental Asian outflow. ** Unavailability of aerosol data during the influence of Path G (i.e., 4–6 October, 2015) over Cape Fuguei.

TEOM with that collected from Cape Hedo (supplement µg m–3). Shimada et al. (2015) also reported the mass of –3 Fig. S2) during the same sampling period. PM2.5 (from PM2.5 (10 ± 5 µg m ) at Cape Hedo, Okinawa in during TEOM) mass levels were 18 ± 12 µg m–3 (range: 2–44 23–26 October, 2010. Maximum (~80% of the total) air µg m–3) and 13 ± 6 µg m–3 (6–30 µg m–3) over Cape Fuguei masses in spring and winter were transported from China and Cape Hedo, respectively. PM2.5 mass over Cape Fuguei to Cape Hedo as estimated from the back trajectory analysis –3 was found higher than that of Cape Hedo in most cases and (Shimada et al., 2011). However, higher PM2.5 (~30 µg m ) also similar/comparable in some cases. The difference in mass were also observed in winter and spring over mass concentrations over two locations (r = 0.02) may be due Kumamoto (Misawa et al., 2017, Fig. 2(a)) mainly due to to the alternation of air masses and the relative contribution the combustion of coal with higher sulfur contents for the from the continental Asian outflows. Both the sampling sites household heating in the northeast area of China were free from local sources and generally received the (Kurokawa et al., 2013). Transboundary air pollution from long-range-transported pollutants from continental outflows the Asian continent due to seasonal monsoons also found associated with a high-pressure system centered over the as a significant contributor to higher aerosol loading over northern region of China and Mongolia. Recently, Jeong Kumamoto (Misawa et al., 2017). and Park (2016) investigated the effects of East Asian During the sampling period, the average PM10 mass winter monsoon on wintertime aerosol concentrations over concentration was 47 ± 10 µg m–3 (number of sampling East Asia by using GEOS-Chem 3D model and reported days, N = 10, range: 29–63 µg m–3) over Cape Fuguei. The that higher concentrations over the southern parts of East mean mass concentrations were 20 ± 9 µg m–3 (N = 10, range: –3 –3 Asia during strong winter monsoon years and opposite 8–37 µg m , and 42 ± 10% in PM10) and 27 ± 4 µg m (N –3 pattern during weak monsoon years. Shimada et al. (2015) = 10, range: 21–35 µg m , 58 ± 10% in PM10) for PM2.5 also inferred that during spring and winter, atmospheric and PM2.5-10, respectively over Cape Fuguei (Table 2(a)), pollutants were transported from the Asian continent to indicating the presence of more coarse aerosols. The aerosol Cape Hedo by migratory high-pressure systems and cold mass was varied widely over this site. The ratio of PM2.5 to fronts. The mean aerosol mass loading (total suspended PM10 (PM2.5/PM10) was 0.4 ± 0.1, which also indicates –3 particles, TSP) at Okinawa was 74 µg m (range: 19–286 relatively higher dominance of coarse aerosols. The PM2.5 µg m–3) during one-year observation period of October level over Cape Fuguei was within the limit of World Health 2009–October 2010 (Kunwar and Kawamura, 2014). Organization (WHO) 24-hour guideline value (25 µg m–3) Moreover, we also compared the gravimetric PM2.5 mass on 8 out of 10 days during sampling period. This finding over Cape Fuguei with that over Cape Hedo and may not suggest health risk of human exposure but climatic Kumamoto (supplement Fig. S3) during the same sampling effect of aerosols at this rural remote site can’t be avoided. period. The average PM2.5 mass concentration (Tables 2(a) The mean levels of PM2.5 and PM2.5-10 mass over Cape and 2(b)) over Cape Fuguei (20 ± 9 µg m–3) was found Fuguei were found comparable with those reported in other comparable with Kumamoto (22 ± 7 µg m–3) but relatively studies conducted over nearby islands and marine locations. lower PM2.5 mass was observed over Cape Hedo (11 ± 5 Chou et al. (2010) reported similar mass of PM2.5 (23 ±

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3013

f

2.5 ) and weight percentages (%) o (%) percentages ) and weight –3 PM 2.5 0.54 ± 0.36 ± 0.36 0.54 ± 1.47 1.09 14.91 ± 15.19 ± 3.80 3.43 17.12 ± 18.05 0.24 0.59 ± 22.96 ± 42.49 0.17 0.26 ± 17.37 ± 25.89 0.69 1.79 ± 11.58 ± 11.69 27.29 ± 57.30 ± 1.28 1.00 3.09 ± 11.76 0.42 0.44 ± ± 4.84 9.89

23 ± 0.29 0.24 3.69 3.52 ± 0.07 0.12 ± ± 1.95 3.90 PM -- 3.01 ± 1.37 ---- 1.20 3.56 ± ---- 0.45 ± 0.43 2.21 ± 1.76 5.59 ± 3.99 2.5-10

Cape Fuguei Cape Fuguei Mt. Bamboo Mt. Lulin PM 2.5 PM , WSIIs, carbonaceous contents, and ratios of different components as mass concentrations (µg m (µg concentrations mass as components different of ratios and contents, carbonaceous WSIIs, , 2.5 Conc. Conc. % w/w Conc. % w/w Conc. % w/w Conc. % w/w Measurements of PM Measurements 3.63 6.99± 8.11 ± 34.67 0.22 0.41 ± 1.65± 0.89 2.19 ± 3.07 9.34 ± 18.38 0.90 1.00 ± 6.80 ± 24.10 0.01± 0.01 0.02 0.05 ± ------± 0.03 0.04 0.10 0.15 ± 0.08 0.07 ± 0.33± 0.29 0.08 ± 0.06 2.71 2.60 ± 0.01 0.02 ± 0.84 ± 0.85 ± 0.09 0.28 1.17 1.79 ± 0.27 1.22 ± 4.54± 0.83 0.01 ± 0.00 0.09 0.13 ± 0.04 0.02 ± 0.40 ± 0.89 2– 2+ ± 0.01 0.04 0.18 0.27 ± 0.04 0.19 ± 0.69± 0.13 0.00 ± 0.00 0.01 0.02 ± <0.01 0.06 ± 0.14 4 2+ 2– ± 0.13 0.22 0.36 0.92 ± 0.01 0.02 ± 0.09± 0.06 0.04 ± 0.01 1.56 1.75 ± 0.00 0.01 ± 0.73 ± 0.69 4 + ± 3.58 7.28 7.24 ± 36.47 0.30 1.46 ± 5.39± 1.02 2.20 ± 3.07 9.26 ± 18.51 0.91 1.02 ± 7.00 ± 24.50 2+ ± 0.01 0.04 0.17 0.27 ± 0.04 0.18 ± 0.67± 0.12 < 0.01 0.01 0.02 ± <0.01 0.06 ± 0.13 ± 1.26 2.21 ±2.56 11.01 0.21 0.31 ± 1.19± 0.82 0.85 ± 1.22 3.71 6.85 ± 0.38 0.33 ± 6.51 ± 3.97 ± 0.35 0.54 1.34 2.98 ± 1.53 2.47 ± 9.74± 6.23 0.48 ± 0.95 5.02 6.15 ± 0.07 0.09 ± 3.18 ± 2.25 ± 0.03 0.13 0.42 0.77 ± 0.12 0.52 ± 1.91± 0.34 0.01 ± 0.00 0.08 0.09 ± 0.00 0.00 ± 0.16 ± 0.24 + ± 0.02 0.07 0.09 0.42 ± 0.08 0.25 ± 0.98± 0.24 0.08 ± 0.06 2.72 2.62 ± 0.01 0.02 ± 0.90 ± 0.81 + – 2– ± 0.36 1.13 4.68 7.17 ± 1.09 4.88 ± 3.31 ± 18.14 ± 0.02 0.02 0.36 0.51 ± 0.16 0.07 ± ± 3.58 1.61 4 3 2+ 4 ± 0.69 0.48 6.31 4.59 ± 2.17 6.82 ± 6.97 ± 24.82 ± 0.07 0.08 1.70 1.96 ± 0.01 0.02 ± ± 0.39 0.59 + 2+ ± 0.12 0.26 0.22 1.19 ± 0.04 0.20 ± 0.73± 0.13 0.05 ± 0.01 1.57 1.77 ± 0.00 0.01 ± 0.73 ± 0.66 – + Samples Samples ss-Ca Ca ss-K ss-SO nss-K nss-Ca SO Total Mass PM Resolved Na 20 ± 9 6 ± 15 100± 0 ± 6 78 27 ± 4 ± 3 18 100 ± 0 8 66 ± 10 13 ± 7 ± 6 100 ± 0 ± 32 85 4 ± 3 2 ± 3 100 ± 0 16 75 ± K NH nss-SO NO Cl Mg nss-Mg Anions WSIIs OC1 OC2 OC3 OC4 OP 8.30 ± 3.28 EC1-OP ± 12.11 4.47 EC2 44.04± 3.12 ± 0.19 0.27 EC3 ± 64.67 6.65 ± 0.30 0.58 OC 10.74 ± 2.00 ± 0.66 1.04 EC ± 16.92 3.19 0.44 1.30 ± ± 0.50 0.61 5.10 39.95 ± OC/EC 0.54 2.69 ± ± 0.54 0.38 8.08 62.93 ± Char-EC/Soot-EC ± 0.23 0.37 1.24 4.28 ± 2.76 ± 3.82 0.03 0.05 ± POC 3.76 ± 5.10 1.35 2.33 ± 0.12 0.19 ± SOC ± 0.03 0.04 26.61 ± 8.39 8.78 1.55 ± 7.97 1.57 ± 0.20 0.36 ± 0.20± 0.13 ± 38.37 10.45 OM ± 0.00 0.00 0.68 1.66 ± 0.06 0.08 ± 0.71± 0.51 1.13 0.97 ± 0.05 0.05 ± ± 1.68 2.81 1.56 1.35± 0.82 1.38 ± 0.13 0.23 ± 0.36 ± 0.29 ---- 17.91 ± 16.08 0.10 0.16 ± ± 0.55 0.42 0.32± 0.25 0.00 0.00 ± 0.33 ± 0.36 28.27 ± 6.07 ± 10.13 38.16 8.33 9.60 ± 0.23± 0. 0.46 ± 0.46 0.01 0.01 ± ---- 3.48 ± 11.94 5.42 6.49 ± 0.60± 0.38 0.32 ± 0.37 0.00 0.01 ± ± 1.44 1.09 1.59 1.77 ± 8.68 ± 11.01 0.46 0.69 ± 0.05± 0.06 0.10 0.23 ± ± 1.06 1.87 5.30 6.40 ± 0.35 ± 0.43 3.72 3.65 0.05± 0.00 ± 0.08 0.17 ± 0.04 0.05 ± ± 3.52 5.90 9.30 ± 6.62 0.11 0.27 ± 4.13 4.61 ± 2.66± 1.90 0.70 2.03 ± 0.27 ± 0.09 6.92 ± 4.29 2.49 8.13 ± 17.30 ± 9.20 0.07 0.13 ± 7.78 ± 11.87 ---- 0.01 ± 0.01 0.19± 0.16 10.44 ± 10.44 0.11 0.12 ± 1.63 ± 1.81 7.32 ± 25.07 4.66 ± 2.67 0.21 0.22 ± -- 0.03 0.08 ± 0.43 0.59 ± 0.04 0.14 ± 24.11 ± 33.24 0.49 ± 0.33 0.96 1.45 ± 2.14 ± 0.82 7.59 ± 7.29 13.56 ± 13.80 0.00 0.01 ± 0.33 0.85 ± 0.82 ± 0.99 0.16 ± 0.10 25.90 ± 37.58 0.10 0.26 ± ---- 7.55 ± 11.26 0.60 0.83 ± ---- Cations ± 1.19 3.80 3.46± 20.55 1.26 6.16 ± 3.46 ± 22.95 the total mass collected over Cape Fuguei, Mt. Bamboo, and Mt. Lulin. Lulin. Mt. and Bamboo, Mt. Fuguei, Cape over collected mass total the Table 2(a).

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Table 2(b). Same as Table 2(a), but for PM2.5 and WSIIs collected over Cape Hedo and Kumamoto. Cape Hedo Kumamoto Samples PM2.5 PM2.5 Conc. w/w % Conc. w/w % Total Mass 11 ± 5 100 ± 0 22 ± 7 100 ± 0 PM Resolved ------Na+ 0.46 ± 0.14 4.59 ± 2.13 0.19 ± 0.06 0.91 ± 0.33 + NH4 0.69 ± 0.35 5.89 ± 1.92 1.90 ± 0.92 8.27 ± 2.31 K+ 0.07 ± 0.02 0.62 ± 0.14 0.19 ± 0.07 0.83 ± 0.07 ss-K+ 0.02 ± 0.01 0.17 ± 0.08 0.01 ± 0.00 0.03 ± 0.01 nss-K+ 0.05 ± 0.02 0.46 ± 0.11 0.18 ± 0.07 0.80 ± 0.09 Mg2+ 0.05 ± 0.02 0.46 ± 0.21 0.02 ± 0.01 0.11 ± 0.05 nss-Mg2+ 0.04 ± 0.01 0.40 ± 0.19 0.02 ± 0.01 0.10 ± 0.04 Ca2+ 0.03 ± 0.02 0.31 ± 0.11 0.19 ± 0.07 0.88 ± 0.37 ss-Ca2+ 0.02 ± 0.01 0.17 ± 0.08 0.01 ± 0.00 0.03 ± 0.01 nss-Ca2+ 0.02 ± 0.02 0.13 ± 0.11 0.18 ± 0.07 0.85 ± 0.36 Cl– 0.20 ± 0.17 2.65 ± 3.31 0.13 ± 0.04 0.63 ± 0.27 – NO3 0.15 ± 0.08 1.45 ± 0.73 1.35 ± 0.63 6.40 ± 3.23 2– SO4 3.17 ± 1.81 26.58 ± 9.27 4.48 ± 2.43 19.13 ± 5.47 2– ss-SO4 0.12 ± 0.04 1.15 ± 0.53 0.05 ± 0.01 0.23 ± 0.08 2– nss-SO4 3.06 ± 1.80 25.44 ± 9.45 4.43 ± 2.42 18.90 ± 5.51 Cations 1.30 ± 0.43 11.87 ± 2.62 2.49 ± 1.01 11.01 ± 1.87 Anions 3.53 ± 1.66 30.68 ± 7.16 5.95 ± 2.60 26.16 ± 5.74 WSIIs 4.83 ± 2.06 42.55 ± 9.09 8.45 ± 3.61 37.17 ± 7.59

–3 –3 1 µg m ) and PM2.5-10 (23 µg m ) collected for 12 hours PM2.5 mass over Mt. Lulin in this study was found closer to over Penghu Island, Taiwan Strait during 2003–2007. The the values reported earlier by Lee et al. (2011). PM2.5 –3 mean PM2.5 (PM2.5-10) mass concentration was 28 µg m levels over high altitude stations in China i.e., Qilian Shan (5 µg m–3) and 10 µg m–3 (6 µg m–3), respectively during Station of Glaciology and Ecologic Environment, Qinghai– January 2003 (Cruise I) and April 2003 (Cruise II) over Tibet Plateau (4180 m amsl) and Quinghai Lake (3200 m Pearl Estuary and waters near Hong Kong (Zhang et al., amsl) were 3 and 6 times higher than that of Mt. Lulin. 2007), clearly indicating the presence of higher fine aerosols. Similar PM2.5 mass over Jungfraujoch, Switzerland (4 ± 2 –3 –3 PM2.5 mass concentrations were 20 ± 16 µg m and 13 ± µg m ) was reported by Krivacsy et al. (2001). PM2.5 mass 11 µg m–3 over Cheji Island, near southern Korea and Sado level around 4 µg m–3 can probably represent global clean Island, Japan, respectively during 1 January–30 June 2002 and pristine area in free troposphere (Lee et al., 2011). (Cohen et al., 2004). The average PM2.5 and PM2.5-10 mass Aerosol mass concentrations varied greatly for different –3 concentrations were 13 ± 6 and 14 ± 15 µg m , respectively samples. Temporal variations in the PM2.5 bulk contents of during the spring 2010 over Dongsha Island, a remote area WSIIs and carbonaceous fractions during the study periods over the northern SCS (Chuang et al., 2013a). over all the study sites are shown in Fig. 3. Bulk anions The PM2.5 mass concentrations over Mt. Bamboo and were found to dominate the distribution, followed by cations Mt. Lulin were 10 ± 13 µg m–3 (N = 14, range: 1–38 µg m–3) and OC over Cape Fuguei, indicating the influences of and 4 ± 3 µg m–3 (N = 14, range: 0–9 µg m–3), respectively. mixed pollution (from anthropogenic, BB, biogenic, and It is worth to note that the PM2.5 mass over Mt. Bamboo natural activities like dust and sea-salt) activity on the –3 –3 was 3 ± 3 µg m (N = 11, range: 1–8 µg m ) and found PM2.5 chemical components. However, OC was found the similar to Mt. Lulin, excluding the episodic days (PM2.5 mass most dominant over Mt. Bamboo and Mt. Lulin followed was 34, 27, and 38 µg m–3 on 29 October, 7 and 8 November, by anions, EC, and cations. EC fractions were found lesser 2015, respectively and all were exceeding the WHO than OC fractions in the PM2.5, providing other distinction guidelines) with more influence by either local or long- of carbonaceous contents. range transported aerosols. The mean levels of PM2.5 mass were comparable with those reported over other high altitude Ion Balance, Neutralization Factors, Ionic Ratios and stations. PM2.5 mass concentrations over Mt. Lulin were 18 Correlations in WSIIs ± 8 µg m–3 (for the air masses transported from the BB Among the WSIIs, anions were found dominant over the area; BB group), 5 ± 2 µg m–3 (from BB source areas during cations at all the study sites (Tables 2(a) and 2(b); the non-BB period; SNBB group), 10 ± 4 µg m–3 (from Figs 3(a)–3(e)). Significant correlations in mass concentrations anthropogenic sources; Anthropogenic group), and 4 ± 2 (Supplement Fig. S4) were estimated between sum of –3 + + + 2+ 2+ µg m (from the oceanic area and the free troposphere cations (Na , NH4 , K , Mg , and Ca ) and sum of anions – – 2– above the 700-hPa pressure level over the Asian continent; (Cl , NO3 , and SO4 ) over Cape Fuguei (r = 0.99 in PM2.5 FT group) during April 2003–April 2009 (Lee et al., 2011). and r = 0.91 in PM2.5-10), Mt. Bamboo (r = 1.00 in PM2.5),

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3015

Fig. 3. Temporal variations in PM2.5, anions, cations, OC, and EC mass concentrations over (a) Cape Fuguei, (b) Mt. Bamboo, (c) Mt. Lulin, (d) Cape Hedo, and (e) Kumamoto.

Mt. Lulin (r = 0.96 in PM2.5), Cape Hedo (r = 0.89 in PM2.5 and r = 0.99 in PM2.5-10), Mt. Bamboo (r = 1.00 in PM2.5), and Kumamoto (r = 0.99 in PM2.5), indicating good PM2.5), Mt. Lulin (r = 0.98 in PM2.5), Cape Hedo (r = 0.90 ion balance for samples. Moreover, in order to determine in PM2.5), and Kumamoto (r = 1.00 in PM2.5), indicating the quality of the analysis, we carried out an ion balance good quality of data-sets and the ions allocate a common estimation using cations and anions with the assumption source origin. The ∑+/∑– ratio is a good indicator to study that most of the ions were in the solutions. The sum of total the acidity of the environment. Average ∑+/∑– ratios > 1 –3 anions (µeq m ) should be equal to the sum of total cations over Cape Fuguei (1.12 ± 0.06 in PM2.5 and 1.11 ± 0.04 in –3 (µeq m ) in the solution as per the electro neutrality PM2.5-10), Mt. Bamboo (1.10 ± 0.23 in PM2.5), and principle and this ratio can be used as a fit indicator to Kumamoto (1.11 ± 0.05 in PM2.5) indicated that the aerosol study aerosol acidity over the sampling sites (Boreddy and samples were evidently alkaline in nature and the anion 2– – Kawamura, 2015). The charge balance between cations deficits were possibly due to the CO3 , HCO3 , and other and anions were estimated as following equations: organic anions (such as acetate and formate). But, the + – ∑ /∑ ratio < 1 over Mt. Lulin (0.85 ± 0.31 in PM2.5) and  Cape Hedo (0.93 ± 0.13 in PM2.5) suggested the acidic nature  Na NH4 K + Cation Equivalent    of aerosols probably due to the lack of H ions. We also 23 18 39 (7) estimated the ion difference by using the following equation 22 Mg Ca   12 20  Ion Difference  % 100 (9)   2    SO4 [NO3 ] Cl  Anion Equivalent    (8) 48 62 35.5 The average ion difference over Cape Fuguei (5.77 ± 2.58% in PM2.5 and 5.19 ± 1.95% in PM2.5-10), Mt. Bamboo Similarly, significant correlations in charge balance (3.96 ± 9.55% in PM2.5), and Kumamoto (5.22 ± 2.22% in (Supplement Fig. S5) were also found between sum of PM2.5) were found well within acceptable range (WMO, cations to anions (µeq m–3) over Cape Fuguei (r = 1.00 in 1994).

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+ – Neutralization factor (NF) is the acid neutralization were higher than NH4 and NO3 over all the sites and capacities of different cations. Acidic nature of aerosols is suggested the more influence of (NH4)2SO4 than NH4NO3 2– – mainly due to the anions like SO4 and NO3 (formed by (Chantara et al., 2012). In addition, the estimated mean + 2– secondary oxidation of NO, NO2, and SO2) and mainly molar ratios of [NH4 ]/[SO4 ] (supplement Table S1) over + + 2+ 2+ neutralized by NH4 , K , Mg , and Ca cations. The role Cape Fuguei (1.57 ± 0.16 in PM2.5), Mt. Bamboo (1.92 ± – + of Cl (in acid production) and Na (in alkalinity) were 0.39 in PM2.5), and Kumamoto (2.34 ± 0.48 in PM2.5) were negligible owing to their marine origins in the form of sea- found closer to 2 (the molar ratio of (NH4)2SO4) whereas salt, which is neutral. The NF for different cations was those over Cape Fuguei (1.10 ± 0.63 in PM2.5-10), Mt. Lulin estimated as by following equations (Keene et al., 1986): (1.31 ± 0.60 in PM2.5), and Cape Hedo (1.20 ± 0.15 in PM2.5) were found closer to 1 (the molar ratio of NH4HSO4). This  [NH ] result suggested the sufficiently formation of (NH4)2SO4 as NF NH   4 (10) 4 2 leading constituent over Cape Fuguei, Mt. Bamboo, and [NO34 nss -SO ] + – Kumamoto sites. The mass ratio of [NH4 ]/[NO3 ] were also estimated (supplement Table S1) and found > 1 over all the [-K]nss  study sites. The estimated mass ratio of [NO –]/[SO 2–] in NF K  (11) 3 4 [NO nss -SO2 ] PM2.5 were found < 1 (supplement Table S1) over Cape 34 Fuguei (0.09 ± 0.05), Mt. Bamboo (0.54 ± 0.61), Mt. Lulin (0.17 ± 0.20), Cape Hedo (0.07 ± 0.05), and Kumamoto nss-Mg2 (0.36 ± 0.23), indicating the dominance of stationary sources 2  NF Mg  (12) (i.e, coal combustion and BB) of sulfur and nitrogen in the [NO nss -SO2 ] 34 atmosphere over the study sites. However, the ratio was > 1 for PM2.5-10 over Cape Fuguei (1.64 ± 0.89) suggested the nss-Ca 2 higher contribution of mobile source (i.e., vehicular NF Ca2   (13)  2 emissions) compared to stationary source in coarse aerosols. + – [NO34 nss -SO ] The strong correlations between Na and Cl were observed (see Table 3) over Cape Fuguei (r = 0.84 in PM2.5 -3 where the concentrations of all WSIIs are in μeq m . The and r = 0.97 in PM2.5-10) and Mt. Bamboo (r = 0.91 in PM2.5), + + 2+ 2+ NF values of NH4 , K , Mg , and Ca are presented in suggesting the similar sources whereas low-to-negative + supplement Table S1. The orders in NF were found as NH4 correlations over Mt. Lulin (r = 0.44 in PM2.5), Cape Hedo + 2+ 2+ + > K > Ca > Mg over Cape Fuguei in PM2.5, NH4 > (r = 0.25 in PM2.5), and Kumamoto (r = –0.24 in PM2.5), 2+ + 2+ Ca > K > Mg over Cape Fuguei in PM2.5-10 and over suggesting the different source origins. It is worth to be + – + Mt. Bamboo, Mt. Lulin, and Kumamoto in PM2.5, and NH4 noted that [Cl ]/[Na ] < 1.8 indicates chlorine depletion 2+ + 2+ + > Mg > K > Ca over Cape Hedo in PM2.5. NH4 was caused by the accumulation of strong acidic anions, found to be the dominant acid neutralizing agent over all the whereas [Cl–]/[Na+] > 1.8 suggests anthropogenic sources sites. However, it can be noted that nss-Mg2+ had a negligible for Cl– (Deshmukh et al., 2013). Average [Cl–]/[Na+] was role on acid neutralizing except the Cape Hedo site. estimated as < 1.8 over Cape Fuguei (0.35 ± 0.42 in PM2.5 + 2– NH4 and SO4 in PM2.5 showed strong correlation over and 1.37 ± 0.20 in PM2.5-10), Cape Hedo (0.45 ± 0.39 in Cape Fuguei (r = 0.98), Mt. Bamboo (r = 0.99), Mt. Lulin PM2.5), and Kumamoto (0.71 ± 0.29 in PM2.5) indicating (r = 0.99), Cape Hedo (r = 0.94), and Kumamoto (r = 0.95). the significant chlorine depletion, while > 1.8 over Mt. + 2– The estimated mean mass ratio of [NH4 ]/[SO4 ] were Bamboo (4.06 ± 1.60 in PM2.5) and Mt. Lulin (2.47 ± 1.52 + 2– – found in between 0.37 (NH4 to SO4 mass ratio) and 0.18 in PM2.5) indicating the anthropogenic sources of Cl + – 2– (NH4 to HSO4 mass ratio) except Kumamoto (supplement significantly from the continental Asian outflows. SO4 , + 2– + 2+ 2+ Table S1). This result indicated that NH4 and SO4 exist in K , Ca , and Mg have both sources i.e., oceanic and the form of (NH4)2SO4 or NH4HSO4 and/or the combination continental. Tables 2(a) and 2(b) shows the ss and nss of the two forms (Kunwar and Kuwamura, 2014). NH4HSO4 components observed over all the aforementioned study 2– + may be dominant over Mt. Lulin and Cape Hedo (the sites. nss-SO4 (a tracer for anthropogenic) and nss-K (a 2– estimated mass ratios were closer to the mass ratio of tracer for BB, Kundu et al., 2010a) were dominant in SO4 + NH4HSO4 whereas (NH4)2SO4 may be dominant over other and K in PM2.5 over all the sites, indicating the significant sites (the estimated mass ratios were closer to the mass influence of both anthropogenic (fossil fuel combustions ratio of (NH4)2SO4). The dominant composition of NH4HSO4 and industrial emissions) and BB in East Asia via a long- was reported over Cape Hedo in TSP aerosol samples range atmospheric transport. Interestingly, ss-Ca2+ was 2+ during October 2009–October 2010 (Kunwar and Kawamura, dominant in Ca over Cape Fuguei (in both PM2.5 and 2+ 2014). The moderate-to-strong correlation coefficients PM2.5-10) and Cape Hedo whereas nss-Ca (a tracer for + – (Table 3) between NH4 and NO3 over Cape Fuguei (r = dust) was dominant over Mt. Bamboo, Mt. Lulin, and 0.57 in PM2.5 and r = 0.83 in PM2.5-10), Mt. Bamboo (r = 0.74 Kumamoto. This result suggested the possible influence of in PM2.5), Mt. Lulin (r = 0.78 in PM2.5), and Kumamoto (r = crustal dust from East Asia over Mt. Bamboo, Mt. Lulin, 2+ 0.47 in PM2.5), revealed the existence of NH4NO3 which and Kumamoto. In addition, almost all Mg over Cape was possibly formed by the reaction of HNO3 and NH3. Fuguei (0.77 ± 0.42% in PM2.5 and 1.91 ± 0.34% in PM2.5-10) + 2– 2+ However, the correlations of NH4 and nss-SO4 in PM2.5 may be produced from oceans and the nss-Mg was only

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3017

Table 3. Correlation coefficients (r) of major WSIIs, OC, and EC for (a) PM2.5 over Cape Fuguei, (b) PM2.5-10 over Cape Fuguei, (c) PM2.5 over Mt. Bamboo, (d) PM2.5 over Mt. Lulin, (e) PM2.5 over Cape Hedo, and (f) PM2.5 over Kumamoto, during the study period. + + + 2+ 2+ – – 2– Na NH4 nss-K nss-Mg nss-Ca Cl NO3 nss-SO4 OC EC (a) PM2.5 over Cape Fuguei. Na+ 1.00 + NH4 –0.61 1.00 nss-K+ –0.56 0.83 1.00 nss-Mg2+ –0.53 0.18 0.11 1.00 nss-Ca2+ –0.66 0.89 0.69 0.79 1.00 Cl– 0.84 –0.69 –0.81 0.47 –0.74 1.00 – NO3 –0.37 0.57 0.40 0.40 0.55 –0.12 1.00 2– nss-SO4 –0.58 0.98 0.88 0.03 0.87 –0.75 0.42 1.00 OC –0.53 0.77 0.93 0.17 0.60 –0.69 0.60 0.76 1.00 EC –0.60 0.86 0.67 0.46 0.77 –0.47 0.88 0.76 0.74 1.00 (b) PM2.5-10 over Cape Fuguei. Na+ 1.00 + NH4 –0.19 1.00 nss-K+ –0.28 0.92 1.00 nss-Mg2+ 1.00 nss-Ca2+ –0.34 0.84 0.91 1.00 Cl– 0.97 –0.36 –0.46 –0.50 1.00 – NO3 –0.41 0.83 0.96 0.88 –0.60 1.00 2– nss-SO4 –0.38 0.79 0.90 0.76 –0.56 0.86 1.00 OC –0.53 0.79 0.72 0.77 –0.67 0.82 0.70 1.00 EC –0.37 0.01 0.31 0.32 –0.42 0.35 0.08 0.50 1.00 (c) PM2.5 over Mt. Bamboo. Na+ 1.00 + NH4 0.93 1.00 nss-K+ 0.88 0.96 1.00 nss-Mg2+ 1.00 nss-Ca2+ 0.74 0.65 0.57 1.00 Cl– 0.91 0.91 0.79 0.68 1.00 – NO3 0.64 0.74 0.70 0.52 0.53 1.00 2– nss-SO4 0.93 0.99 0.95 0.64 0.92 0.64 1.00 OC 0.90 0.94 0.88 0.64 0.89 0.80 0.91 1.00 EC 0.88 0.90 0.82 0.62 0.86 0.74 0.88 0.95 1.00 (d) PM2.5 over Mt. Lulin. Na+ 1.00 + NH4 0.05 1.00 nss-K+ –0.89 0.43 1.00 nss-Mg2+ 1.00 nss-Ca2+ –0.47 0.06 0.35 1.00 Cl– 0.44 0.76 0.38 –0.15 1.00 – NO3 0.57 0.78 0.33 –0.22 0.92 1.00 2– nss-SO4 0.12 0.99 0.37 0.02 0.78 0.79 1.00 OC 0.45 0.15 –0.21 –0.23 0.47 0.39 0.23 1.00 EC 0.61 0.13 –0.45 –0.52 0.40 0.37 0.23 0.87 1.00 (e) PM2.5 over Cape Hedo. Na+ 1.00 + NH4 0.18 1.00 nss-K+ 0.21 0.88 1.00 nss-Mg2+ 0.99 0.16 0.21 1.00 nss-Ca2+ 0.00 0.22 0.46 0.12 1.00 Cl– 0.25 –0.81 –0.65 0.27 –0.19 1.00 – NO3 0.43 –0.12 0.15 0.53 0.65 0.31 1.00 2– nss-SO4 0.18 0.94 0.72 0.14 0.08 –0.78 –0.25 1.00 OC ------

3018 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017

Table 3. (continued). + + + 2+ 2+ – – 2– Na NH4 nss-K nss-Mg nss-Ca Cl NO3 nss-SO4 OC EC EC ------(f) PM2.5 over Kumamoto. Na+ 1.00 + NH4 0.12 1.00 nss-K+ 0.25 0.96 1.00 nss-Mg2+ 0.80 –0.17 –0.17 1.00 nss-Ca2+ 0.59 0.16 0.31 0.42 1.00 Cl– –0.24 –0.45 –0.40 –0.30 0.04 1.00 – NO3 –0.76 0.47 0.33 –0.74 –0.29 0.15 1.00 2– nss-SO4 0.40 0.96 0.95 0.08 0.26 –0.56 0.19 1.00 OC ------EC ------

2– 0.05 ± 0.02% in PM2.5 and zero in PM2.5-10. However, nss- It is worth to note that over Cape Fuguei nss-SO4 was 2+ Mg was found relatively higher over Cape Hedo (0.40 ± mainly distributed in PM2.5 while lower values were observed 2+ 2– + 0.19% in PM2.5 and 88.20 ± 0.00% in Mg ) and Kumamoto in PM2.5-10. The larger variations in nss-SO4 and NH4 2+ (0.10 ± 0.04% in PM2.5 and 88.20 ± 0.00% in Mg ) possibly fractions of the total PM2.5 indicate that the aerosol collected from the continental Asian outflow. K+ may arise from crustal at the Cape Fuguei site have contributions from anthropogenic material, sea-salt, BB, and coal combustion (Bougiatioti et sources from continental Asian outflows. The variation in 2+ + 2– al., 2013). The correlation coefficients between nss-Ca NH4 was consistent with that in nss-SO4 on the linear + and nss-K were higher over Cape Fuguei (r = 0.69 in PM2.5 correlation coefficients in PM2.5 (r = 0.98) and PM2.5-10 (r = and r = 0.91 in PM2.5-10) whereas moderate-to-lower over Mt. 0.79), indicating the association of both ions over Cape – + 2– Bamboo (r = 0.57 in PM2.5), Cape Hedo (r = 0.46 in PM2.5), Fuguei. Though NO3 , NH4 , and nss-SO4 were mainly Mt. Lulin (r = 0.35 in PM2.5), and Kumamoto (r = 0.31 in from anthropogenic sources (Seinfeld and Pandis, 2006), – 2– PM2.5), revealing the possible influence of crustal source of NO3 exhibited moderate correlation with nss-SO4 in PM2.5 + 2– + K over Cape Fuguei. The nss-SO4 and NH4 in PM2.5 (r = 0.42) and higher correlation in PM2.5-10 (r = 0.82). This – aerosols showed strong correlations (r > 0.94, Table 3), finding implied that NO3 ions did not exist in fine particles 2– + representing neutralization of acidic SO4 by basic NH4 but in coarse particles (Chuang et al., 2013a). Among the + – over all the aforementioned sites. Higher positive correlation WSIIs, Na and Cl contributed moderately to the PM2.5 2– + (r ≥ 0.88) between nss-SO4 and nss-K was found over while much higher in PM2.5-10, indicating that sea-salt aerosol Cape Fuguei (r = 0.88 in PM2.5 and r = 0.9 in PM2.5-10), Mt. appeared to be the main constituent of coarse particles. Bamboo (r = 0.95 in PM2.5), Cape Hedo (r = 0.72 in PM2.5), Similar result was reported over Dongsha Island (Chuang + – and Kumamoto (r = 0.95 in PM2.5), whereas lower correlation et al., 2013a) in northern SCS. Na and Cl exhibited over Mt. Lulin (r = 0.37), might be attributed to formation consistent variations in PM2.5 (r = 0.84) and PM2.5-10 (r = of secondary aerosols. Strong-to-moderate correlations 0.97) caused by the moderate effect of chlorine loss in 2+ 2+ (Tables 3(a)–3(f)) were observed between nss-Ca and PM2.5 aerosols (as discussed in next sub-section). Mg and – 2+ 2– 2+ NO3 (except Kumamoto), nss-Ca and nss-SO4 (only Ca were also found higher in coarse aerosols. The nss- 2+ over Cape Fuguei and Mt. Bamboo), attributed to either Ca in PM2.5-10 (0.33 ± 0.29%) was found too low and coagulation between fine particles of these acidic crustal possibly came from the soil dust. The nss-K+ and nss-Ca2+ aerosols or oxidation of gaseous precursors on the crustal showed significant correlation (r = 0.91, Table 3(b)) in particles (Aymoz et al., 2004; Koçak et al., 2007b). PM2.5-10 and indicated the notable influence of soil dust. 2– Likely, nss-SO4 was the most abundant species among Distribution of WSIIs PM2.5 WSIIs (Table 2(a) and Figs. 4(c) and 4(d)), with The distribution of WSIIs as weight percentages of average concentrations of 2.19 ± 3.07 µg m–3 and 1.00 ± –3 PM2.5 and PM2.5-10 over Cape Fuguei in the present study 0.90 µg m , comprising 18.38 ± 9.34% and 24.10 ± 6.80% are shown in Figs. 4(a) and 4(b), respectively. Table 2(a) of the total PM2.5 mass over Mt. Bamboo and Mt. Lulin, 2– shows that WSIIs accounted for 64.67 ± 6.65% and 62.93 respectively. In addition to nss-SO4 , other major WSIIs + – + ± 8.08% in PM2.5 and PM2.5-10 over this site. The most observed were NH4 followed by NO3 and nss-K . The 2– 2– + 2+ abundant species (Table 2(a)) was nss-SO4 (34.67 ± 8.11%) nss-SO4 , nss-K , and nss-Ca components were contributed + 2– + 2+ among PM2.5 WSIIs, followed by NH4 (11.01 ± 2.56%), almost (> 95%) to the total SO4 , K , and Ca aerosols over + – – Na (7.17 ± 4.68%), Cl (4.59 ± 6.31%), NO3 (2.98 ± Mt. Bamboo and Mt. Lulin, indicating the less influence of 1.34%), and nss-K+ (0.92 ± 0.36%). On the contrary, the sea-salt aerosols. Similar to Cape Fuguei, the concentrations – 2– + most abundant species was Cl (24.82 ± 6.97%) followed of nss-SO4 and NH4 over Mt. Bamboo and Mt. Lulin + – 2– by Na (18.14 ± 3.31%), NO3 (9.74 ± 6.23%), nss-SO4 were also widely varied, as revealed in Figs. 4(c) and 4(d) + (1.65 ± 0.89%), and NH4 (1.19 ± 0.82%) in PM2.5-10. Sea- and indicated the contributions from anthropogenic sources salt was found to be the main constituent of coarse particles. from the northern and northeastern China. The distribution

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3019

Fig. 4. Distributions of WSIIs as weight % of total (a) PM2.5 over Cape Fuguei, (b) PM2.5-10 over Cape Fuguei, (c) PM2.5 over Mt. Bamboo, (d) PM2.5 over Mt. Lulin, (e) PM2.5 over Cape Hedo, and (f) PM2.5 over Kumamoto.

+ + of NH4 was found similar over Mt. Bamboo (6.85 ± 3.71% the highest contribution nss-K over Mt. Bamboo (1.75 ± in PM2.5) and over Mt. Lulin (6.51 ± 3.97% in PM2.5). 1.56% in PM2.5) followed by Cape Fuguei (0.92 ± 0.36% in – NO3 was contributed the highest over Mt. Bamboo (6.15 ± PM2.5) and Mt. Lulin (0.73 ± 0.69% in PM2.5) was observed. 5.02% in PM2.5) followed by Mt. Lulin (3.18 ± 2.25% in This result showed possible influence of BB over Mt. PM2.5) and Cape Fuguei (2.98 ± 1.34% in PM2.5). Similarly Bamboo site.

3020 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017

However, similar findings in distributions of WSIIs were 1999) during November 1996–January 1997, and 8.7 at seen over Cxape Hedo and Kumamoto sites. Similar in East China Sea (Nakamura et al., 2005) during September– 2– findings to other locations, nss-SO4 was also found the October, 2002. The order of WSIIs over Mt. Bamboo 2– + – 2+ – + + 2+ most abundant over Cape Hedo (25.44 ± 9.45%) and (SO4 > NH4 > NO3 > Ca > Cl > K > Na > Mg ) + – Kumamoto (18.90 ± 5.51%) followed by NH4 and NO3 was found similar with those high-altitude sites i.e., Qinghai– 2– + (Table 2(b)). Larger variations of nss-SO4 and NH4 over Tibet Plateau and Quinghai Lake in China, Manora peak in these two locations (Figs. 4(e) and 4(f)) revealed the India, Lulang and Nepal Climate Observatory at Pyramid contributions from anthropogenic emissions mainly from the (NCO-P) in Nepal (Table 4). Similarly, the average values continental Asian outflow. The variation in Na+ and Cl– were and pattern of WSIIs over Mt. Lulin in this study was found found significant over Cape Hedo owing to the vicinity of matched with the results reported by Lee et al. (2011) and the oceanic air masses. Strong correlations (r > 0.94, see also found comparable with other high-altitude sites i.e., Mt. 2– + Tables 3(e)–3(f)) between nss-SO4 and NH4 revealed Tateyama, Mt. Norikura, and Mt. Fiji in Japan (Table 4). 2– strong neutralization of acidic sulfate. The nss-SO4 and nss-K+ showed higher correlation over Kumamoto (r = 0.95) Chloride Deficit than Cape Hedo (r = 0.72) and suggested the significant The chloride deficit (Clloss in %) decreases as the distance formation of secondary aerosols over Kumamoto. Both Cape from the sea or the coast increases due to the depletion of – Hedo and Kumamoto were influenced by eastward drift of Cl (Park et al., 2016). Clloss was estimated by using the transboundary aerosol intrusions from the Asian continent following equation (Yao and Zhang, 2012). into the NPR region and resulted in worse air quality in Japan (Moreno et al., 2013; Kunwar and Kawamura, 2014;  1.798 Na Cl  Shimada et al., 2015; Zhu et al., 2015; Misawa et al., 2017). Cl % 100 (14) The cause findings over these two locations in this study were loss  1.798  Na found corroborated with the previous results in literatures. The major WSIIs in PM2.5 over coastal location and + – islands in East Asia i.e., Cape Fuguei, Cape Hedo, and where, [Na ] and [Cl ] represents the mass concentrations + – –3 Kumamoto in this study were found comparable (Table 4) of Na and Cl in µg m , respectively. The mean Clloss was with those collected over Okinawa, Japan in PM2.1 during found more substantial over Cape Fuguei i.e., 80.75 ± 18 March–13 April 2008 (Deshmukh et al., 2016) and over 23.53% (range: 39–99%) and 23.93 ± 10.99% (12–54%) Gosan, Jeju Isalnd, Korea in PM2.5 aerosols during 18 March for PM2.5 and PM2.5-10, respectively. Relatively lower mean 2– and 5 April 2005 (Kuwata et al., 2005). SO4 was found of Clloss i.e., 74.88 ± 21.64% (24–98%) and 60.35 ± 15.84% + – the most abundant species followed by NH4 and NO3 (see (44–84%) were estimated over Cape Hedo and Kumamoto, – Table 4) over all the locations. On contrast, Cl was found respectively. The Clloss was not found significant over Mt. the highest from Okinawa aerosols (TSP) followed by Na+, Bamboo and Mt. Lulin sites and hence not discussed here. 2– – + SO4 , NO3 , and NH4 during October, 2009–October, The Clloss (%) estimated in this study was compared with 2010 (Kunwar and Kawamura, 2014), indicating the higher marine aerosols sampled at coastal regions and open sea contribution of sea-salt to the coarser aerosols. However, locations in East Asia and over the world (supplement + – the highest Na was found over Cape Hedo followed by Cl , Table S2). Fine mode aerosols showed higher Clloss as 2– + 2+ – + SO4 , NH4 , Mg , NO3 , and K during 23–26 October, compared to the coarse mode. Park et al. (2004) accounted + 2010 (Shimada et al., 2015). The concentrations of K for Clloss (55% for fine mode particles) and (16% for coarse- (0.26 µg m–3), Mg2+ (0.18 µg m–3), and Cl– (0.49 µg m–3) mode particles) during the normal periods over Jeju Island over Gosan, Jeju Island in PM2.5 aerosols (Kuwata et al., in southern Korea. The estimated Clloss was up to 50% in 2005) were closely matching our observations over Cape spring over Okinawa Island (Kunwar and Kawamura, 2014). 2– Fuguei. SO4 was found the highest over Kumamoto (during Clloss was nearly 86–98% for PM2.5 and 29–30% for PM2.5-10 – + + – March–April, 2011) followed by NO3 , NH4 , Na , Cl , over the sea waters between Taiwan and Dongsha Island in 2+ + 2+ Ca , K and Mg (Moreno et al., 2013). The mean mass SCS (Hsu et al., 2007). The Clloss in PM2.5 were 77.3 ± –3 – 2– concentrations (in µg m ) of NO3 (nss-SO4 ) were 0.58 ± 9.9% (Asian Continent Trajectory; ACT); 77.9 ± 23.4% 0.07 (2.12 ± 0.42) over Chichijima island during 2001– (Philippine Trajectory; PPT), and 59.9 ± 10.0% (West 2012 (Boreddy and Kawamura, 2015), 0.16 ± 0.08 (0.67 ± Pacific Trajectory; WPT) over Dongsha Island in northern 0.27) over Fanning island during 1981–1986, 0.16 ± 0.09 SCS (Chuang et al., 2013a). Likely, the Clloss in PM2.5-10 over Nauru, 0.10 ± 0.07 over Funafuti, 0.11 ± 0.05 over were 51.4 ± 10.4% (ACT); 95.6 ± 5.3% (PPT), and 54.6 ± American Samoa during 1983–1987, and 0.12 ± 0.08 over 24.5% (WPT) over Dongsha Island (Chuang et al., 2013a). Rarotonga (Savoie et al., 1989). The mass concentrations The Clloss in PM2.5 at the offshore site and over sea in the –3 2– (in µg m ) of SO4 over Cape Fuguei (7.28 ± 3.58) was Taiwan Strait ranged in 16.2–19.2% and 7.6–20.4%, also found comparable with 7.3 at Anmyon Island, South respectively (Li et al., 2016). The higher Clloss over East Korea (Hong et al., 2002) during September 1998–August China Sea was too much lower than those on the SCS. 1999, 6.9 at Cheju Island, South Korea (Carmichael et al., Moreover, the East China Sea and the Taiwan Strait received 1996) during March 1992–May 1993, 6.4 at Tokchok Island, abundant amount of acidic gases from Asian outflows (Streets South Korea (Lee et al., 2002) during April 1999–March et al., 2000; Carmichael et al., 2002; Li et al., 2016), 2000, 9.7 at New Territories, Hong Kong (Zhuang et al., whereas air masses transported toward the SCS were not

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3021 ., 2016 ., 2010 ., 2015 ., 2003 ., 2013 ., 2005 ., 2005 ., 2008 2008 ., et al ., 2014 ., 2002 ., 2002 orldwide. orldwide. ., 1996 ., 1996 ., 2015 . 2007 ., 2013 ., 2001 ., 2010 et al et al et al ., 2011 et al et al ., 2007 ., 2007 ., 2007 ., 2007 ., 2007 ., 2014 et al et al et al et al et al et al et al et al et al et al et al et al et al et al

– Cl + 0.02 0.08 This Study Study This 0.08 0.02 Na

2+ 0.01 Mg

2+ Ca + K + 4 NH 2– 4 r islands andAsia inr islands high-altitude Mountain East and sites w SO – 3 0.54 0.54 7.28 2.21 0.26 0.15 3.17 Study 0.69 0.07 0.13 0.07 This 0.48 1.13 Study 0.03 ------This 0.20 0.46 1.35 4.48 1.90 0.19 Study 0.19 0.02 0.48 This 0.13 0.19 2.20 0.85 0.05 0.09 1.02 0.33 0.08 0.01 Study This 0.02 0.07 0.02 0.002 3.1 7.7 0.14 10.1 3.7 2.4 1.44 0.7 0.14 3.96 1.57 0.07 Deshmukh 0.26 0.06 0.12 0.44 --- 0.18 Kuwata 0.43 0.49 0.38 3.7 Shimada 17.0 20.9 0.07 0.77 0.29 0.06 0.06 0.48 0.05 0.08 0.01 0.08 1.26 0.04 0.16 0.01 0.06 0.37 1.43 0.23 0.07 Lee 0.38 4.45 0.08 Xu 0.57 0.08 0.11 Kido Osada 0.12 0.06 Zhang 0.23 0.07 0.13 0.67 2.26 0.024 0.02 Pio 0.02 0.01 0.02 0.09 0.04 0.25 0.2 Pio 0.07 4.6 7.0 1.0 0.4 0.5 0.2 0.6 0.5 Moreno 0.28 0.68 0.14 0.05 0.11 1.29 Decesari 0.03 0.46 0.15 0.01 0.02 Pio 0.04 0.03 0.02 0.11 0.12 Nyeki 2.5 2.5 2.5 2.5 2.5 2.5 2.1 2.5 10 2.5 2.1 2.1 2.5 2.5 10 2.5 10 2.5 10 PM PM PM TSP 1.81 2.54 0.51 0.30 0.48 0.60 5.19 10.8 Kunwar 2014 and Kawamura, PM PM

------Comparison of WSIIs mass concentrations from this study with othe with study this from concentrations mass WSIIs of Comparison Table 4. NCO-P, Nepal NCO-P, Nepal 2006–May Feb. 2008 5079 PM Lulang, Nepal Nepal Lulang, 2009 2008–Jul. Jul. 3360 TSP 0.21 1.07 0.06 0.35 0.07 0.33 0.1 Zhao Okinawa, Japan 2010 23–26 Oct., Mt. Bamboo, Taiwan Taiwan Mt. Bamboo, 2015 Oct.–Nov., 1103 PM Qomolangma (Mt. Everest)Qomolangma (Mt. Mt. Sonnblick, Austria Aug. 2009–Jul. 2010 4276 2003–Oct. Oct. 2005 TSP 3160 0.2 0.43 PM 0.03 0.02 0.88 0.04 0.07 0.02 Cong Kumamoto, Japan Oct.–Nov., 2015 -- Gosan, Korea Korea Gosan, 2005 Apr., 5 and Mar. 18 Japan Mt. Norikura, Qinghai Lake, China 1 Sep.–8 2000 Oct., IndiaManora Peak, Jun.–Sep., 2010 2005–Jul. Feb. 2008 PM 1950 3200 TSP PM 0.65 4.74 0.47 1.46 Ram Okinawa, Japan Okinawa, Japan 2008 Apr., 18 Mar.–13 Mt. Fuji, Japan 2001–Sep. Jul. 2002 3776 TSP 0.11 1.44 0.39 0.29 0.01 0.05 0.02 Suzuki RongbukGlacier, China Qinghai–Tibet Plateau, China Jul. 2010–Jul. 2011 10–25 Sep., 2003 4180 6500 PM TSP 0.14 0.41 0.02 0.04 Ming Mt. Lulin, Taiwan Oct.–Nov., 2015 2862 PM Okinawa, Japan Kumamoto, Japan 2009–Oct. Oct. 2010 Mt. Lulin, Taiwan Mar.–Apr.,2011 2003–Apr. Apr. 2009 2862 PM PM Location Period Height (m) Size NO Size (m) Height Period Location Cape Fuguei, Taiwan Taiwan Fuguei, Cape Japan Hedo, Cape 2015 Oct.–Nov., 2015 Oct.–Nov., -- -- PM Southwestern Germany Oct.2003–Oct. 2005 1205 PM Jungfraujoch, Switzerland Switzerland Jungfraujoch, 2000 & 1999 Sep.–Nov., 3580 TSP 0.14 0.35 0.13 < 0.01 0.09 Henning Central FranceCentral Switzerland Jungfraujoch, Jul.–Sep., 1995 2003–Oct. Oct. 2005 3580 1450 PM PM Mt.Tateyama, Japan Mt.Tateyama, Nov.–Feb.,1995–2000 2450 PM

Note: content The study are shown this of as bold.

3022 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 only from South China but also from BB emitted particularly (11.94 ± 3.48% in PM2.5; 2.66 ± 1.90% in PM10-2.5), followed 2– from the Indochina Peninsula (Arndt et al., 1997; Chuang et by the nss-SO4 over Cape Fuguei (Table 2(a)). By contrast, al., 2013a). In the Antarctic coastal site, Clloss was observed EC exists mostly in PM2.5 (1.77 ± 1.59%) as compared to only in the polluted summer but not in the clean winter PM2.5-10 (0.19 ± 0.16%). However, OC comprised the (Jourdain and Legrand, 2002). Clloss was observed only for dominant bulk resolved component in PM2.5 (Table 2(a)) the finer aerosols over the Arctic (Hara et al., 2002). Lesser over Mt. Bamboo (33.24 ± 24.11%) and Mt. Lulin (37.58 ± values of Clloss indicated that the strength of emissions of 25.90%) followed by the water soluble anions (26.61 ± acid gases would not be the most critical controlling factor 8.39% for Mt. Bamboo and 28.27 ± 6.07% for Mt. Lulin) Clloss of over East coast of US (Bermuda), NE Pacific and EC (13.80 ± 13.56% for Mt. Bamboo and 11.26 ± 7.55% Ocean, tropical northern Atlantic Ocean, northern Indian for Mt. Lulin). Excess concentration of OC was reported in Ocean, and NW Mediterranean Sea (Keene and Savoie, winter in urban regions of China (Wang et al., 2011). Our 1998; Johansen et al., 1999, 2000; Sellegri et al., 2001; study sites were receiving most of the air parcels from the Newberg et al., 2005). Contrarily, the tropical Arabian Sea northern China suggesting the additional contribution of OC showed higher Clloss as compared to the abovementioned from BB emissions as burning of crop residues (wheat oceanic sites i.e., 89 ± 9% and 25.6 ± 21.3% for PM2.5 and straw and corn stalk) and fire-woods were significant in PM2.5-10 (Johansen and Hoffmann, 2004). urban Beijing from late autumn to winter (Wang et al., 2009; Yu et al., 2013). Moreover, high concentrations of Carbonaceous Contents OM were observed over Beijing during winter time (Wang The distributions of eight temperature-resolved et al., 2006; Zhang et al., 2008). Among the 8 carbonaceous carbonaceous fractions of PM2.5 collected over the study fractions analyzed in PM2.5 (PM2.5-10), the OC3 > OC2 > sites are shown in Fig. 5. OC was found the second most OC4 > OP > OC1 (OC3 > OC2 > OP > OC4 > OC1) order abundant resolved component in both PM2.5 and PM2.5-10 in OC fractions and EC1-OP > EC2 > EC3 (EC1-OP >

Fig. 5. Distributions of carbonaceous fractions as weight % of total (a) PM2.5 over Cape Fuguei, (b) PM2.5-10 over Cape Fuguei, (c) PM2.5 over Mt. Bamboo, and (d) PM2.5 over Mt. Lulin.

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3023

EC2 > EC3) order in EC fractions were observed over carbonaceous aerosols in Kathmandu valley, Godavari, and Cape Fuguei (Table 2(a) and Figs. 5(a)–5(b)). The least Nepal were expected to be biofuel combustion (cow-dung amount of OC1 fraction may be due to the rapid evaporation cake, wood, and agricultural waste) and BB activities of this fraction in BB smoke after emission into the (Carrico et al., 2003; Decesari et al., 2010; Stone et al., atmosphere (Chuang et al., 2013b; Lee et al., 2016). It is 2010). Similarly, major contribution of carbonaceous well documented that OC3 is often used as tracer for BB aerosols in Manora Peak and Mt. Lulin were attributed to (Chuang et al., 2013b; Lee et al., 2016). Similarly, nonvolatile be BB emissions (Ram et al., 2008; Chuang et al., 2014). EC1-OP (char-EC) is one of the major components in BB Carbonaceous aerosols in Europe were found to be emissions (Chuang et al., 2013b; Lee et al., 2016) and used attributed to BB emissions mainly in winter and fossil fuel for source apportionment of BB (Cao et al., 2005; Han et combustions in summer (Krivacsy et al., 2001; Gelencsér al., 2007; Han et al., 2009). Both, OC3 and EC1-OP were et al., 2007; Pio et al., 2007). found the most abundant fractions of OC and EC contents, respectively in both PM2.5 and PM2.5-10, over Cape Fuguei and OC/EC Ratio, POC vs. SOC, and Char-EC/soot-EC Ratio revealed the significant contribution of BB from continental The correlations between OC and EC mass concentrations Asian outflow. The highest EC1-OP in both PM2.5 and PM2.5-10 (Table 3) were significant, i.e., Cape Fuguei (r = 0.74), Mt. suggested the char dominated EC over this site from the Bamboo (r = 0.95), Mt. Lulin (r = 0.87), indicating common BB emissions in continental Asian outflow. The sequence emission sources and transport processes. OC/EC ratio is order of OCs showed the relatively higher contribution of generally used to study the origin of carbonaceous aerosols OP in PM2.5-10 than that of PM2.5. OP was also reported as (Turpin and Huntzicker, 1995). Typical emission sources the most abundant carbonaceous fraction in PM2.5-10 over a of carbonaceous aerosols commonly included vehicle exhaust near-source BB region at Chiangmai, northern Thailand (OC/EC: 2.5–5.0; Schauer et al., 2002), kitchen emissions during March–April, 2010 (Chuang et al., 2013b). Similarly, (OC/EC: 4.3–7.7; See and Balasubramanian, 2008), coal OP was also observed the most abundant carbonaceous smoke (OC/EC: 2.5–10.5; Chen et al., 2006), and BB fraction in both PM10 and PM2.5, in a rural area during smoke (OC/EC: 3.8–13.2; Zhang et al., 2007). OC/EC ratios have haze events in northwestern China (Zhu et al., 2016). Likely, been reported as lower than 1.0 for diesel vehicles (Watson the orders of fractions in OC (EC) were OC3 > OC1 > et al., 2001), 2.05–2.36 for gasoline engines (Liu et al., OC2 > OC4 > OP (EC2 > EC1-OP > EC3) and OC3 > 2006), 2.7 for coal combustion (Watson et al., 2001), and OC1 > OC2 > OC4 > OP (EC2 > EC1-OP > EC3) for Mt. 9.0 for BB activity (Cachier et al., 1989). OC/EC ratio of Bamboo (Fig. 5(c)) and Mt. Lulin (Fig. 5(d)), respectively. 5.1 was attributed to coal combustion and BB (Cao et al., EC3 was found almost negligible over all the sites. The 2005) and 1 attributed to vehicle and traffic-related sources highest OC3 fraction in OCs suggested the significant (Cao et al., 2006). The estimated mean OC/EC ratio over influence of BB emissions, while the highest EC2 fraction Cape Fuguei was 17.91 ± 16.08 (range; 2.65–54.67) with in ECs suggested the soot dominated EC from anthropogenic the highest peak on 1 November (54.67) and a secondary emissions over Mt. Bamboo and Mt. Lulin sites. Overall these peak (35.40) on 31 October. It is worthy to note that on two sites were found influenced by the both anthropogenic both the abovementioned days (31 October and 1 November); and BB from the Asian outflows during the IOP. Cape Fuguei received the long-range transported BB Table 5 summarizes the OC and EC levels observed at emissions (through BT Path F) from the northern and the Cape Fuguei, Mt. Bamboo, and Mt. Lulin with other northeastern China. The mean OC/EC ratio in PM2.5-10 background, rural, and high-elevation sites. The average aerosols over Cape Fuguei (17.30 ± 9.20) was found same concentrations of OC and EC at Cape Fuguei (OC: 2.81 ± as that of PM2.5 (17.91 ± 16.08) and indicating that all EC 1.68 µg m–3 and EC: 0.42 ± 0.55 µg m–3) were found were present in fine mode. comparable with those at islands and back-ground/rural A higher value of OC/EC (32.4; estimated from the stations in Japan, Korea, China, and other parts of the world. reported OC and EC values) was reported over Okinawa OC and EC concentrations were ranged 0.89–6.07 µg m–3 Island, Japan in spring, 2008 due to the long-range-transport and 0.02–2.01 µg m–3 at Cape Fuguei. These background EC BB from East Asia (Deshmukh et al., 2016) and well concentrations were also found similar with 0.13–0.30 compared with our results. Moreover, the OC/EC ratios µg m–3 of EC measured at Mt. Waliguan (Tang et al., 1999), were 4.8 for BB aerosols in Phimai, Thailand (Li et al., 2013) 0.08–0.43 µg m–3 of EC from the Gosan marine GAW station and 5.7 in Chiangmai, Thailand (Chuang et al., 2013b), 6.8 of Korea (Kim et al., 1999), 0.53 µg m–3 of EC from S. in Sonla, Vietnam (Lee et al., 2016), 9.1 in Tanzania, East Pietro Capofiume in Europe (Decesari et al., 2001), and Africa (Mkomo et al., 2010), 18.9 in Rondonia, Brazil 0.8 µg m–3 of EC from the Galveston background site in (Kundu et al., 2010b), 15.4 in Georgia, USA (Lee et al., north America (Fraser et al., 2002). The mass range of OC 2005), and 17.8 in Wyoming, USA (Pratt et al., 2011). and EC were 1.6–5.2 µg m–3 and 0.2–1.3 µg m–3, respectively Table 5 also compares the OC/EC ratio over Cape Fuguei over the rural and background locations (Table 5). together with those from different back-ground and rural Likely, the OC and EC concentrations over Mt. Bamboo locations in East Asia and in the world. Chou et al. (2010) (OC: 1.63 ± 1.81 µg m–3 and EC: 0.49 ± 0.33 µg m–3) and reported the annual range of 2.6–3.0 (OC/EC) over Cape Mt. Lulin (OC: 0.85 ± 0.33 µg m–3 and EC: 0.26 ± 0.10 Fuguei in a previous study. Shimada et al. (2016) reported µg m–3) were found comparable with those reported over a value of 3.0–4.3 for OC/EC ratio over Okinawa, Japan. other high altitude mountains. The major sources of Kim et al. (2000a) estimated comparably higher value of 14.4

3024 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017

., 2011 2011 ., ., 2016 ., 2016 ., 2010., ., 2016 2016 ., ., 2005 ., 2010 ., 2010 ., 2011 ., 2011 et al ., 2014 ., 2014 ., 2003 ., 2003 ., 2003 ., 2003 et al ., 2008 ., 2008 ., ., 2011 2011 ., ., 2010 2010 ., ., 2010 ., ., 2010 ., ., 2012 ., 2013 ., 2000a et al et al ., 2008 ., 2008 ., 2007 ., 2007 ., 2012 ., 2012 ., 2009a ., 2009a ., 2009 ., 2009 ., 2001 ., 2001 et al et al et al ., 2013 ., 2013 et al et al et al et al ., 2009 ., ., 2016 ., 2011 ., ., 2013a 2013a ., et al et al et et al et et al et al et al et al et al de Mountain sites in East East in sites Mountain de et al et al et al et al et al et al et al et al et al et al et et al et al ± 0.33 ± 0.33 0.26± 0.10 ± 1.20 3.56 This study 2.81 ± 1.68 0.42± 0.55 16.08 ± 17.91 This study 1.63 ± 1.81 0.49± 0.33 ± 1.37 3.01 This study 1.8–4.5 0.7–1.5 2.6–3.0 10 0.43 4.41 Chou 0.6 ± 1.6 Lee 0.2 ± 0.5 2.1 ± 3.8 3.1 0.5 ± 1.0 1.4 ± 5.2 3.8 0.4 ± 1.2 1.6 ± 0.6 4.3 Lin Lim Shimada 32.4 0.7 ± 1.3 3.0 Deshmukh 6.1 0.3 ± 0.4 0.5 1.9 ± 4.3 1.8 5.2 Chuang 5.0 3.5 Zhou 0.8 Wang 4.5 Li 4.4 ± 4.8 0.8 ± 1.0 4.8 Stone 3.1 ± 0.9 2.8 ± 1.2 0.34 ± 0.18 11.9 0.36 ± 0.31 12.2 Zhang Zhang 10.6 2.6 3.1 3.9 0.3 11.9 Jia Qu 14.4 4.4 ± 5.8 14.4 1.0 ± 1.5 1.5 2.6 0.9 9.6 15.3 Engling Carrico Carrico 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.1 10 10 2.5 2.5 2.5 10 10 2.5 10 10 10 2.5 4500 TSP 0.4 0.04 12.0 4500 TSP Cao -- 3.2 0.5 6.8 Vercauteren . 2005 4500 TSP 0.5 0.1 29–32.1 Cao ons and OC/EC ratio from ons high-altitu ratio this study rural/back-ground OC/EC and from sites with other and May, 2005 Sep.–Nov., 2010Sep.–Nov., 18 Mar.–13 Apr., 2008 60 -- PM TSP 1.4 ± 0.5 0.2 ± 0.1 7.1 2014 Kunwar and Kawamura, Comparison of OC concentrati and EC mass Tengchong Apr.–May, 2004 1640 PM 1640 2004 Tengchong Apr.–May, Langtang, Nepal 1999–Jan. Oct. 2000 3920 1.8 ± 1.2 0.5 ± 0.5 3.5 Carrico Godavari, Nepal Nepal Godavari, 2006 1600 PM Mt. Bamboo, Taiwan Taiwan Mt. Bamboo, 2015 Oct.–Nov., 1103 PM Cape Fuguei, Taiwan Taiwan Fuguei, Cape 2015 Oct.–Nov., -- PM Daihai 2005–2007 TSP 12.4 2.0 6.2 Han 6.2 2.0 12.4 TSP Lulang, Nepal Daihai 2005–2007 Mt. Hua, China Jul. 2008–Jul. 2009 Jan. 10–22, 2009 3360 2160 TSP 4.3 ± 2.1 TSP 0.5 ± 0.4 6.9 ± 2.9 1.7–58.4 0.9 ± 0.6 8.2 ± 3.0 Zhao Li Mount ChinaHeng, Mount China Lu, Mar.–May, 2009 Namco, China Muztagh Ata, China 2011 Aug.–Sep., 1269 PM 1474 2003–Feb Dec. Jul. 2006–Jan. 2007 PM 4730 TSP 1.7 ± 0.8 0.1 ± 0.1 31.9 ± 31.1 Ming Muztagh Ata, China Qinghai Lake, China Mar.–May., 2004 & Mar.– Nov. 2011–Nov. 2012 Nagarkot, Nepal 3200 NCO-P, Nepal PM 2000 Feb–May, Post-monsoon 2150 5079 PM 1.4 0.1 14 Decesari Akdala, China China Akdala, Whitbourne, UK Morogoro, Tanzania Switzerland Chaumont, 1998–Mar. 1999 Apr. 2006 Mar.–Apr., 2006 Nov.–Dec., 2003 ------1.7 4.5 ± 0.9 3.2 ± 1.5 PM 0.52 ± 0.16 0.6 1.1 ± 0.5 8.7 ± 3.2 2.9 ± 1.9 Mkomo 2.8 Pongpiachan, 2006 Hueglin Houtem, Belgium Sep. 2006–Sep. 2007 Cape Taiwan Fuguei, 2003–2007 -- PM Taiwan Mt. Lulin, Mt. Lulin, Taiwan 2015 Oct.–Nov., 2012 2003–Apr. Apr. 2862 2862 PM 0.85 Deokjeok, Korea Deokjeok, Korea 2005–2007 -- PM Dongsha, Taiwan Taiwan Dongsha, Gosan, Korea Gosan, Korea Japan Okinawa, 2010–2013 Shangri-La, China 1996 Dec. Jan. 1997 2005 Nov., 6–8, -- 2006 -- PM -- PM PM -- 3.3 ± 0.6 PM 0.2 ± 0.04 14.4 ± 3.5 Kim Mount Tai, China Mount Tai, China 2007 Mar.–Apr., 1533 PM Daihai, China China Zhuzhang, 2005 2004–Mar. Jul. 2007 Apr.–May, 3580 1221 PM TSP 8.1 1.8 5.0 Han Kathmandu, Nepal Feb.–May, 2000 2150 PM Location Period Height (m) Size OC EC OC/EC References References OC/EC EC OC Size (m) Height Period Location High-Altitude Mountain Sites Back-ground/Rural Sites Sites Back-ground/Rural Asia and worldwide.Asia and Table 5. Table

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3025

± 3.5 for OC/EC ratio over a rural location in Gosan, Korea. OC/EC ratio was 10 in Gosan, Jeju Island in December 1996 (Lee et al., 2001), 11.9 in Shangri-La, southwest tip of China (Zhang et al., 2008), and 12.2 in Akdala, northwest tip of China (Zhang et al., 2008) over back-ground remote

., 2007 ., 2007 2007 ., locations. OC/EC ratios in back-ground stations in Europe ., 2001 ., 2006 2006 ., ., 2001 ., 2001 (Table 5) were comparably lower (2.8–6.8) than East Asia et al et al et al et ., 2015 ., 2015 ., 2008 ., 2008 ., 2010 et al et al and attributed mainly to anthropogenic emissions. ., 2007 et al

et al The mean OC/EC ratio was 3.01 ± 1.37 (range: 1.15– et al et al

et al et 5.16) and 3.56 ± 1.20 (range: 2.32–7.06) over Mt. Bamboo and Mt. Lulin, respectively during the study period. OC/EC ratio was 4.8 ± 1.5 (BB group), 3.4 ± 2.0 (SNBB group), 3.8 ± 1.5 (anthropogenic group) and 4.3 ± 1.9 (FT group), during April 2003–April 2012 over Mt. Lulin (Chuang et al., 2014). The OC/EC ratios over mountains in the present study were normally lower than most OC/EC ratios observed at other high-altitude mountain sites, as shown in Table 5. Lower OC/EC values of 3.6 in Jungfraujoch, Switzerland (Krivacsy et al., 2001), 2.6 in Tengchong, China (Engling et al., 2011), 3.1 in Puy de Dome, France (Gelencser et al., 2007), 4.9 in Southwestern Germany (Gelencser et al., 2007), and 4.3 in Qinghai Lake (Li et al., 2013a) over high altitude stations were influenced by free tropospheric air masses of different origins with respect to seasonal variations. Higher OC/EC ratios obtained in the present study than those

reported over the high altitude stations i.e., Namco (31.9 ± . ) 31.1), Muztagh Ata (2.9–32.1), Lulang (1.7–58.4) mountain 1.1 1.1 0.7 0.3 0.2 0.2 3.9 1.1 3.1 0.02 1.4 0.3 9.5 Watson 0.3 Gelencsér 3.6 4.9 Gelencsér Krivacsy Gelencsér 1.6 0.2 7.2 Pio

1.5 0.2 8.8 Marenco (Table 5) may be attributed to the very low EC level. 2.5 2.5 10 2.5 2.5 1 2.5 Carbonaceous aerosols with the OC/EC ratio more than continued 2.0 can be considered to indicate the significant contribution ( of SOC (Gray et al., 1986; Zhang et al., 2008). The relative high OC/EC ratios observed at Cape Fuguei (17.9 ± 16.0), especially for regionally representative aerosols may result Table 5. both from differences in primary source composition as 3106 PM 3106 1205 PM 1205 well as the presence of a regional background of SOC. The average quantities of POC and SOC estimated in PM2.5 over Cape Fuguei were 0.77 ± 1.30 µg m–3 (4.61 ± 4.13%) and 1.87 ± 1.06 µg m–3 (8.13 ± 2.49%), respectively (Table 2(a)). Similarly, POC and SOC estimated in PM2.5-10 over Cape Fuguei were 0.12 ± 0.11 µg m–3 (0.45 ± 0.43%) and 0.59 ± 0.43 µg m–3 (2.21 ± 1.76%), respectively (Table 2(a)).

POC and SOC were found higher in PM2.5 than PM2.5-10 aerosols. The average POC concentrations were 0.54 ± 2003 2003 2003 2003 –3 0.36 µg m (15.19 ± 14.91% in PM2.5) and 0.59 ± 0.24 Dec. 2002, Jan and Dec and 2002, Jan Dec. Dec. 2002, Jan and Dec and 2002, Jan Dec. –3 µg m (25.89 ± 17.37% in PM2.5) over Mt. Bamboo and Mt. Lulin, respectively. Likewisely, the SOC mass concentrations –3 were 1.09 ± 1.47 µg m (18.05 ± 17.12% in PM2.5) and 0.26 –3 ± 0.17 µg m (11.69 ± 11.58% in PM2.5) over Mt. Bamboo and Mt. Lulin, respectively. The formation of SOC was found two times higher than that of POC over Cape Fuguei. The POC formation over the Mt. Bamboo was found lower than that of Mt. Lulin while Mt. Bamboo showed higher percentage of SOC formation than that of Mt. Lulin, indicating the possible influence of BB at Mt. Bamboo. The estimated average OM concentration in PM2.5 over Cape Fuguei, Mt. Bamboo, and Mt. Lulin were 5.90 ± 3.52 µg m–3 –3 Germany Germany (25.07 ± 7.32%), 3.43 ± 3.80 µg m (42.49 ± 22.96), and –3 Puy de Dôme, Puy de Dôme, Central France Monte Italy Cimone, Oct., 2004 30Jun.–6 2276 PM Schauinsl and Southwestern Southwestern Schauinsl and Central France France Central Switzerland Jungfraujoch, 1998 Jul.–Aug. Oct. 2003–Oct. 2005 3580 1450 PM PM Sonnblic, Austria Sonnblic, Austria Oct.–Dec. 2002 3106 PM Manora Peak, India India Peak, Manora India Peak, Manora 2005 Feb.–Mar., 2008 2005–Jul. Feb. 1950 1950 TSP TSP ± 5.2 8.2 11.6 ± 1.2 1.3 ± 3.4 7.3 1.8 Ram 6.6 Ram Qomolangma (Mt. Everest) Station Station Everest) (Mt. Qomolangma 2010 Aug. 2009–Jul. 4276 TSP 1.2 ± 1.4 0.3± 0.2 (1.91–43.8) 6.7 Cong Mount USA Zirkel, Dec. 1994–Nov. 1995 3224 PM 1.79 ± 0.69 µg m (57.30 ± 27.29%), respectively. Location Period Height (m) Size OC EC OC/EC References References OC/EC EC OC Size (m) Height Period Location

Note: The content of this study are shownas bold. are study Note: The content this of The ratio of char-EC to soot-EC in PM2.5 is more effective

3026 Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 indicator for BB contribution of carbonaceous aerosols concentration and surface chemistry characterization over than the previously used OC/EC ratio because the later can the abovementioned sites (Cape Fuguei, Mt. Bamboo, and be affected by SOC formation (Han et al., 2007, 2009). Mt. Lulin) under different BT pathways (as presented in Char-EC is formed during relatively low combustion Table 1 and Figs. 2(a)–2(c)). Higher concentrations of PM2.5, temperatures from BB activity, whereas soot-EC is formed WSIIs, OC, and EC were observed for the representative at high combustion temperatures from coal combustion or pathway of Asian outflow over Cape Fuguei (Path C + Path from vehicle exhaust (Zhu et al., 2010). The char-EC/soot- F), Mt. Bamboo (Path F), and Mt. Lulin (Path F) during the EC ratios can be as high as 22.6 for BB activity and as low IOP (supplement Table S3). Fig. 6 shows the relative mass as 0.6 for vehicle exhaust (Chow et al., 2004). The char- fraction (%) of PM2.5 and its various components for EC/soot-EC ratios were 11.6 and 1.9 for BB and coal different BT pathways during the IOP. Moreover, higher – combustion, respectively, in Xi’an City, China (Cao et al., concentrations of BB tracers (i.e., NO3 , OC3, and EC1-OP) 2005). Cao et al. (2006) subsequently obtained char-EC/soot- were also observed when these sites were under the influence EC ratios of 0.3 and 0.7 for diesel and gasoline exhausts, of continental Asian outflow (supplement Table S3). The respectively near roadsides. Chen et al. (2007) observed order of relative mass fraction (%) for different BT pathways – char-EC/soot-EC ratios as high as 31 for sagebrush burning in NO3 was found to be as Path C + Path F > Path A > in a laboratory experiment. In this present study, the average Path B (Cape Fuguei), Path F > Path A > Path G > Path D char-EC/soot-EC ratios were calculated as 8.78 ± 7.97 (range; (Mt. Bamboo), and Path F > Path A > Path B > Path G > 0.67–27.54), 0.82 ± 0.99 (range: 0.07–2.98), and 0.83 ± Path E (Mt. Lulin). Likely, the sequence of relative mass 0.60 (range: 0.04–1.99) over Cape Fuguei, Mt. Bamboo, and fraction (%) for different BT pathways in OC3 was found Mt. Lulin, respectively. The char-EC/soot-EC ratio over to be as Path C + Path F > Path B > Path A (Cape Fuguei), Cape Fuguei was found similar to the value of 11.6 from Path F > Path D > Path A > Path G (Mt. Bamboo), and BB sources (Cao et al., 2005), 9.4 ± 3.8 for BB sources in Path F > Path G > Path B > Path A > Path E (Mt. Lulin). Chiang Mai, Thailand (Chuang et al., 2013b), 9.6 ± 10.1 Additionally, the sequence of relative mass fraction (%) for for BB aerosols in Sonla, Vietnam (Lee et al., 2016) and different BT pathways in EC1-OP was found to be as Path suggested relatively more influence of BB emissions. Both F > Path B > Path A (Cape Fuguei), Path F > Path A > Path D the sites, Mt. Bamboo and Mt. Lulin, showed relatively > Path G (Mt. Bamboo), and Path F > Path G > Path A > lower values of char-EC/soot-EC ratio may be due to the Path B > Path E (Mt. Lulin). In addition to above, the OC/EC presence of mixed type aerosols (both anthropogenic and and char-EC/soot-EC ratios were also found the highest for BB) from the air masses coming from urban China. It is the Asian outflow path over all the sites. These results worth to note that the mean concentration (in µg m–3) of suggested that the continental Asian outflow significantly char-EC (Mt. Bamboo: 0.24 ± 0.29; Mt. Lulin: 0.12 ± 0.07) influence the overall PM2.5 mass concentrations and its BB was more or less same with soot-EC (Mt. Bamboo: 0.27 ± components over the islands and mountains in East Asia. 0.09; Mt. Lulin: 0.14 ± 0.08). This ratio was 3.9 ± 3.5 (BB We also selected some episodic days as representative of group), 0.4 ± 0.4 (SNBB group), 0.9 ± 0.9 (anthropogenic BB emissions from continental Asian outflow over all the group) and 0.3 ± 0.4 (FT group), during April 2003–April above mentioned sites during the IOP. PM2.5 aerosol mass 2012 over Mt. Lulin (Chuang et al., 2014). was observed the highest over Cape Fuguei (37 µg m–3) on 29 October, when it was the second highest over Mt. Bamboo –3 –3 Long-Range Transported Haze from Continental Asian (34 µg m ; the highest was 38 µg m on 8 November) and Outflow Mt. Lulin (8 µg m–3; the highest was 9 µg m–3 on 28 We further investigated the relationship among WSIIs and October). The PM2.5 mass was found lesser with distance carbonaceous species to verify the influence of anthropogenic from the Asian continent and sea-level altitude. Fig. 7 – and BB emissions from Asian outflow. NO3 is a tracer of shows the PM2.5 chemical species distributions over three anthropogenic (Kundu et al., 2010a) and BB (Lee et al., aforementioned locations on 29 October. Among the three 2– + 2016), mainly derived from coal combustions, BB, and sites, SO4 , K , OC, and EC fractions were observed the vehicular emissions (Kundu et al., 2010a). EC is a tracer of highest over Cape Fuguei and indicated the higher influence incomplete combustion of fossil fuels and BB (Kundu et of both anthropogenic and BB emissions. The highest PM2.5 – + al., 2010a). Positive correlation between NO3 and nss-K mass over Cape Fuguei was associated with the highest 2– –3 over Cape Fuguei (r = 0.4 in PM2.5 and r = 0.96 in PM2.5-10), mass of SO4 (12.51 µg m and 34.04% in PM2.5), OC –3 –3 Mt. Bamboo (r = 0.70 in PM2.5), and Mt. Lulin (r = 0.33 in (6.07 µg m and 16.52% in PM2.5), and EC (2.01 µg m – PM2.5) suggested the association of NO3 with BB and and 5.47% in PM2.5). It is also worth to note that, on that – –3 anthropogenic emissions from continental Asian outflow. particular day, NO3 (1.62 µg m and 4.40% in PM2.5), OC3 –3 –3 Kunwar and Kawamura (2014) also reported a positive (2.31 µg m and 6.30% in PM2.5), EC1-OP (1.94 µg m – + correlation between NO3 and nss-K over Okinawa (r = and 5.28% in PM2.5), and char-EC/soot-EC ratio (27.54) 0.65) in winter and suggested the influence of BB emissions. were also found the highest (for both mass concentrations From the above analysis and discussions, we found the and % contributions in PM2.5) over Cape Fuguei with possible and significant influence of continental Asian respect to other days. These results suggested 29 October outflow on the ambient aerosols in East Asia. However, in as a representative day of both anthropogenic and BB order to quantify the possible contribution from the influence over Cape Fuguei during the IOP. Similarly, the –3 continental Asian outflow, we analyzed the PM2.5 mass highest mass concentrations of PM2.5 (38 µg m ), OC

Pani et al., Aerosol and Air Quality Research, 17: 3006–3036, 2017 3027

Fig. 6. Relative mass fraction (%) of different BT pathways in PM2.5 and its components over Cape Fuguei (top-panel), Mt. Bamboo (mid-panel), and Mt. Lulin (bottom-panel) during the IOP. Similar colors for the BT paths are used here as Figs. 2(a)–2(c). For the interpretation of references to the colors in this figure legend, the reader can refer to the web version of this article.

(6.36 µg m–3), EC (1.26 µg m–3) and all the BB tracers [Ca] as per the availability with an assumption that both – –3 + –3 –3 (NO3 : 3.67 µg m ; nss-K : 0.07 µg m ; OC3: 1.63 µg m ; were from the crustal influences and other metals (Al, Si, EC1-OP: 0.92 µg m–3) were recorded over Mt. Bamboo on Ti, and Fe) were not used because of their unavailability of 8 November, indicating a representative BB influenced measurements. The observed and reconstructed PM2.5 mass day. Similarly, the highest concentration of all the BB exhibited satisfactory correlations (Figs. 8(a)–8(c)) over – –3 –3 tracers i.e., NO3 (0.24 µg m ), OC3 (0.43 µg m ), and Cape Fuguei (r = 0.98) and Mt. Bamboo (r = 0.99) whereas EC1-OP (0.25 µg m–3) were observed on 10 November little poor over Mt. Lulin (r = 0.89). The unavailability of over Mt. Lulin. This observation suggested the influence of other crustal metals may be introduced some uncertainty long-range transported BB emissions from continental into the calculation of the reconstructed PM2.5 mass. Asian outflow to the background and free-tropospheric Relative contribution (%) of different components in PM2.5 aerosols over Mt. Lulin. reconstructed mass (Figs. 8(d)–8(f)) followed the sequence of [(NH4)2SO4] > [OM] > [NH4NO3] > [Sea-Salt] > [EC] > Reconstruction of PM2.5 Mass [Soil], [OM] > [(NH4)2SO4] > [NH4NO3] > [EC] > [Soil] > We reconstructed the surface PM2.5 mass concentrations [Sea-Salt], [OM] > [(NH4)2SO4] > [NH4NO3] > [Soil] = by using the IMPROVE algorithm (Hand et al., 2011) as [Sea-Salt] over Cape Fuguei, Mt. Bamboo, and Mt. Lulin, follows: respectively. Relative contribution (%) of [(NH4)2SO4] was found greater than [NH4NO3] in PM2.5 reconstructed mass PM2.5 = [(NH4)2SO4] + [NH4NO3] + [OM] + [EC] + (Figs. 8(d)–8(f)) for all the sites, which was corroborated with [Sea-Salt] + [Soil] (15) our previous discussions in this study i.e., correlation between + 2– NH4 and nss-SO4 in PM2.5 were found higher than that of 2– + – where [(NH4)2SO4] = 1.375 × [SO4 ], [NH4NO3] = 1.29 × NH4 and NO3 over all the sites. Relative contribution of – – [NO3 ], [OM] = 2.1 × [OC], [Sea-Salt] = 1.8 × [Cl ] (Shettle [OM] in PM2.5 reconstructed mass (Figs. 8(d)–8(f)) was and Fenn, 1979), and [Soil] = 1.63 × [Ca] (Patterson, 1981). found comparable with observations (Table 2(a)) for Cape In this study, for soil estimation we used [Ca2+] in place of Fuguei, Mt. Bamboo, and Mt. Lulin. When comparing with

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Fig. 7. PM2.5 chemical species distribution on 29 October over (a) Cape Fuguei, (b) Mt. Bamboo, and (c) Mt. Lulin.

Fig. 8. Correlations between the observed and reconstructed PM2.5 mass over (a) Cape Fuguei, (b) Mt. Bamboo, and (c) Mt. Lulin. Relative contribution (%) of different components in PM2.5 reconstructed mass over (d) Cape Fuguei, (e) Mt. Bamboo, and (f) Mt. Lulin. the observations (Table 2(a)), the contribution of [EC] in contribution of [Sea-Salt] over Cape Fuguei was also found - + PM2.5 reconstructed mass (Figs. 8(d)–8(f)) was found in little well accordance with the previously discussed [Cl ]/[Na ] lower side for Cape Fuguei, while largely underestimated ratio over the sampling site. Relative contribution of [Soil] for Mt. Bamboo and Mt. Lulin aerosols. The highest followed the sequence of Mt. Bamboo > Mt. Lulin > Cape

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Fuguei and found well accordance with the % contribution both anthropogenic and BB emissions from continental 2+ of Ca (Table 2(a)) in PM2.5. Asian outflow plays an important role in regulating chemical properties of wintertime aerosols over remote islands and CONCLUSIONS mountains in East Asia.

This study is a component of an IOP carried out during ACKNOWLEDGMENTS 25 October–10 November, 2015 over various sites in East Asia. Ambient aerosols were collected over islands and This work was supported by the Ministry of Science and mountains sites (i.e., Cape Fuguei, Mt. Bamboo, Mt. Lulin, Technology of Taiwan (MOST 103-2111-M-008-001 and Cape Hedo, and Kumamoto) in East Asia and analyzed for 104-2111-M-008-002) and by the Taiwan Environmental mass concentrations, WSIIs and carbonaceous fractions on Protection Administration (EPA-104-U1L1-02-101 and the basis of the US-IMPROVE protocol and correction EPA-105-U1L1-02-A046). Graduate students and assistants method. The main goal of this study was to characterize the helped aerosol sampling at our study sites are appreciated. wintertime surface aerosol chemistry over remote islands The authors also gratefully acknowledge the NOAA Air and mountains in East Asia. Resources Laboratory for the provision of the HYSPLIT The highest PM2.5 aerosol mass was found over Kumamoto model used in this study. MODIS fire-counts used in this (22 ± 7 µg m–3) and followed by Cape Fuguei (20 ± 9 µg m–3), study was available at https://disc.sci.gsfc.nasa.gov/neespi/ Cape Hedo (11 ± 5 µg m–3), Mt. Bamboo (10 ± 13 µg m–3), data-holdings/mod14cm1.shtml. Raw data used to produce –3 and Mt. Lulin (4 ± 3 µg m ). The PM2.5 collected in this the results of this manuscript can be obtained from Neng- study showed that WSIIs accounted for ~65% of the total Huei Lin ([email protected]) and Chung-Te Lee aerosol mass over Cape Fuguei with ~14% of carbon fractions ([email protected]) upon request. The authors would (the sum of OC and EC). On the contrary, carbon fractions like to thank the Editor and two anonymous reviewers for were the higher contribution (~48%) over Mt. Bamboo and their insightful comments and suggestions which substantially Mt. Lulin as compared to WSIIs (38%). WSIIs accounted improved this manuscript. for ~40% in PM2.5 over Cape Hedo (42.55 ± 9.09%) and Kumamoto (37.17 ± 7.59%). Chemical analysis showed that SUPPLEMENTARY MATERIALS 2– + nss-SO4 was the most abundant species followed by NH4 , + – – + Na , Cl , NO3 , and nss-K . Significant correlations (r > Supplementary data associated with this article can be 0.9) in charge balance of ions suggested the good quality of found in the online version at http://www.aaqr.org. data-sets and the ions shares common source origins. The study showed more influence of (NH4)2SO4 and NH4HSO4 REFERENCES – 2– than NH4NO3. Mass ratio of [NO3 ]/[SO4 ] in PM2.5 were found < 1, indicating the dominance of stationary sources Arndt, R.L., Carmichael, G.R., Streets, D.G. and Bhatti, N. 2– (i.e., coal combustion and BB) during the IOP. The nss-SO4 (1997). 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