Atmospheric Arsenic Deposition in Chiayi County in Southern Taiwan

Long-Full Lin1, Shu Hsien Wu2, Sheng-Lun Lin3,4*, John Kennedy Mwangi2, Yi-Ming Lin5, Chia-Wei Lin2, Lin-Chi Wang4,6, Guo-Ping Chang-Chien4,7

1 Department of Environmental Engineering, Kun Shan University, Yung Kang, Tainan City 71003, Taiwan 2 Department of Environmental Engineering, National Cheng Kung University, Tainan City 70101, Taiwan 3 Center of General Education, Cheng Shiu University, Kaohsiung City 83347, Taiwan 4 Super Micro Mass Research and Technology Center, Cheng Shiu University, Kaohsiung City 83347, Taiwan 5 College of Environmental Science and Engineering, South China University of Technology, Guangzhou 510640, China 6 Department of Civil Engineering and Engineering Informatics, Cheng Shiu University, Kaohsiung City 83347, Taiwan 7 Department of Cosmetic and Fashion Styling, Cheng Shiu University, Kaohsiung City 83347, Taiwan

ABSTRACT

Although arsenic contamination of underground water in southern Taiwan is well known, few studies examine atmospheric arsenic deposition in this area, which might be the major source of such pollution to the soil, water, and even underground water. This research focused on the atmospheric arsenic concentration, dry and wet depositions, and the As distribution around Chiayi County, located in the south of Taiwan. Eight sampling sites are used, both upwind and downwind of an area with heavy industrial and human activities. All samples were collected by a PS-1 high volume sampler at each site, pretreated by a digestion process, and further analyzed with an ICP-MS. The results show that the arsenic deposition flux ranged from 65.0 to 473 μg/m2-month in Chiayi County. This deposition flux has no significant seasonal variation, based on the multiple trend results obtained from pooling the dry and wet deposition data. The average dry deposition flux of As ranged from 34 to 161 μg/m2-month during the sampling year, and had the opposite trend to the wind speed. Additionally, the correlations between atmospheric arsenic concentration and PM levels were significant, supported by the low p-value (< 0.01) at a 99% confidence level. Meanwhile, the highly linear correlation between As and PM concentrations was also evaluated. The amount of precipitation was statistically correlated to the wet deposition flux (11.3–414 μg/m2-month with a p-value = 2 × 10–7 and r-value = 0.9306. Furthermore, the composition of the As mass concentrations in ambient air were dominated by As (V) in both fall (66.4%) and winter (68.9%). According to the GIS spatial analysis of the As concentration in the dry season, from October to March, the As contribution of local emissions were not significant. Consequently, this study indicates that the atmospheric As around Chiayi County might be sourced from the upwind northern area, and mainly deposited through wet scavenging.

Keywords: Arsenic; Dry deposition; Wet deposition.

INTRODUCTION world since they were able to form stable compounds that could be bio-accumulated in living organisms and affect The level of atmospheric arsenic (As) level and its their immune system (Duker et al., 2005; Sanchez-Rodas deposition are issues of public concern, due their adverse et al., 2007; Serbula et al., 2010; Bermudez et al., 2012). effects on both human health and the environment (Contreras Arsenics is not only considered as a carcinogen, but has also et al., 2009; Kang et al., 2011; Shi et al., 2012). Arsenic been shown to have harmful effects on the bladder, liver, compounds have been identified as Group-I carcinogens, kidney, and lung, and cause several non-cancer diseases, such which can enter the human body through respiration, as diabetes mellitus, hypertension and coronal heart disease ingestion, and skin absorption (Liu et al., 2007). Arsenic (Englyst et al., 2001; Cantor and Lubin, 2007; Coronado- poisoning cases have been reported in various areas of the Gonzalez et al., 2007; Boamponsem et al., 2010; Fang et al., 2012b). In general, arsenic compounds are emitted to the atmospheric environment from both natural sources and * Corresponding author. Tel.: +886-7-731-0606 ext. 2605; human activities, and further contained in suspended Fax: +886-7-733-2204 aerosol in the atmosphere (Lopez-Anton et al., 2006; Kang E-mail address: [email protected] et al., 2011). The natural sources of arsenic compounds are

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mainly released from volcanic activity, since they are widely arsenic in the PM2.5 and PM10 particles has been shown to distributed in the earth’s crust (2 mg/kg) (Wedepohl, be 1.09–9.51 ng/m3 and 1.27–13.65 ng/m3, respectively 1991). Throughout the related high temperature processes, (Tsai et al., 2003). Fang et al. (2012) also reported that the some arsenic compounds are adsorbed on volcanic ash and highest concentration of As from dry deposition occurred in deposited to the ground, while the others remain in winter in central Taiwan for the years 2009 and 2010, and atmospheric aerosols, and these are then subject to long- found that it was highly correlated with the steel, electronic range transportation in the troposphere (Thomaidis et al., and plastic industries, as well as the amount of fossil fuel 2003; Wang et al., 2010; Chen et al., 2012; Fang et al., combustion by a thermal power plant. 2012a). However, human activities account for three times Incidents of arsenic contamination and chronic arsenicism more emissions of arsenic compounds to the environment have been investigated on the south-west coast of Taiwan, than volcanic activity, and these mostly come from mining, with 7,418 cases of hyperpigmentation, 2,868 of keratosis, municipal solid waste incineration, fossil fuel combustion and 360 of black-foot disease being observed in a population processes, metallurgical facilities, and vehicles (Wang and of 40,421 people in 37 villages, as well as some cases of Mulligan, 2006; Contreras et al., 2009; Boamponsem et al., cancer (Mandal and Suzuki, 2002). However, almost no 2010; Lee and Nguyen Thi, 2011; Ny and Lee, 2011; Tian studies have examined the issue of arsenic deposition, which et al., 2011; Chen et al., 2012). Nevertheless, the burning could directly affect the quality of the soil, water, and of firework during the special festival in Asian culture was underground water around southern Taiwan. Therefore, the reported as one of the main sources of trace metal, current study examines the dry and wet depositions of arsenic including As (Do et al., 2012). in the aerosols and suspended particles in the atmosphere Anthropogenic emissions of arsenic could accumulate of Chiayi County, which is located in the southern Taiwan. and concentrate on smaller size particulate matters, which This county contains both agricultural and industrial areas, cannot be completely removed by air pollutant control devices. and the seasonal and regional variations of arsenic These forms of particle-based arsenic have relatively long concentration and deposition are both considered in this work. atmospheric residence times before deposition, and eventually The results of this study are expected to be of considerable cause pollution several kilometers downwind from the sources value with regard to developing better control strategies for (Bencko and Symon, 1977; Saxena et al., 2008; Csavina et arsenic in the atmosphere over Taiwan. al., 2011; Alahmr et al., 2012). The major removal mechanisms for arsenic suspended in MATERIALS AND METHODS air include gravitational dry deposition and wet scavenging (Andreae et al., 1998; Tsopelas et al., 2008; Coskun et al., Sampling Strategy 2009; Harmens et al., 2010). In dry deposition, arsenic All the samples used in this study were obtained from usually presents as a mixture of arsenites As (III) and Chiayi County in southern Taiwan, with eight sampling arsenates As (V) (Mandal and Suzuki, 2002, Serbula et al., sites chosen upwind and downwind of the potential sources 2010). Both of these can directly cause harmful effects by of arsenic emission, as shown in Fig. 1. Five major sources dermal contact and inhalation, and are predominantly were examined, including Minsyong, Touciao, Jiatai, and absorbed on particulate matters, especially PM10 and PM2.5 Puzi industrial parks and Chiayi City. Sites A (23°35'54.69"N; (Schwartz et al., 1996; Shi et al., 2011; Shi et al., 2012). In 120°23'26.13"E) and B (23°33'4.26"N; 120°25'38.73"E) were addition, the dry deposition of particle-based arsenic on the chosen to provide upwind data, for Minsyong, Touciao, and surfaces of water and soil is considered to be an indirect Jiatai industrial parks and Chiayi City in both cold and warm but important threat to human health (Steinnes et al., 2011; seasons, while sites C (23°29'24.46"W; 120°17'30.09"E), Fang et al., 2012a). The dry deposition flux of total arsenic D (120°19'56.83"W; 23°27'28.82"N) and E (23°25'33.47"N; was reported as 241.39 μg/m2-month in an urban area of 120°23'49.82"E) were chose to collect the downwind data. Shanghai, which is higher than the amounts reported for Additionally, sites G and H were located nearby Jiatai and suburban (174.33 μg/m2-month) and rural areas (141.89 Puzi industrial parks, in order to monitor the arsenic levels μg/m2-month) (Shi et al., 2012). For wet deposition, the in the ambient air that may be related to industrial activity. arsenic adsorbed by aerosols and suspended particles might Finally, site F was located in a rural area that was far from deposit on water and soil through rain, dew, and snow both industrial activity and Chiayi City. (Tinggi, 2003). In a coastal area, the arsenic wet deposition All the meteorological information, PM2.5, PM10, and total flux was reported to be around 20–836 μg/m2-month, varying suspended particle (TSP) concentrations for the sampling sites with the seasonal meteorological conditions. Even in a high from January 2011 to June 2012 was taken from the Xingang, altitude atmosphere, the content of Mt. Everest’s ice core Puzi, and Chiayi City stations of the Taiwan Air Quality has shown to have rising arsenic levels since the 1970s, Monitoring Network (Taiwan Environmental Protection representing a significant amount of arsenic accumulation Administration, 2012). The average daily temperature of (Hong et al., 2009). The impacts of arsenic to these media the sampling area, taken from three reference sites, ranged are a cause for serious concern due to their high toxicity, from 15.1°C in January to 29.5°C in August, while the persistency, and the ability of long-range transportation in precipitation ranged from 11.3 to 415 mm, and the mean the environment (Ng et al., 2003, Kang et al., 2011, De wind speed ranged from 1.86 to 3.22 m/s from January 2011 Temmerman et al., 2012). to June 2012. The precipitation in Chiayi during 2011– In Tainan City, Taiwan, the total amount of particle-based 2012 showed relatively low values in fall and winter, while

934 Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013

Fig. 1. Locations of the sampling sites. higher values existed in spring and summer. Therefore, the 255 L/min for a total of 720 m3 with 48-hour continuous “dry seasons” is defined as October to March, and the “wet sampling. A quartz fiber filter was used to capture the season” started from April to September in this study. The particulate samples after they had first been conditioned in atmospheric PM2.5, PM10, and TSP concentration were an electric desiccator operating at 25 ± 5°C and 45 ± 5% illustrated as Fig. 2, comparing with the precipitation and humidity for 24 hours. After two days of sampling, the temperature records. The ambient air TSP level in the particle-based As samples were then stored in a sealed plastic sampling area varied from the lower values in May, June, bag. The chemical analysis of As, As(III), and A(V) was July, and August to the higher levels in November, December, based on NIEA A302.73C and M105.00B, and included an January, and February. Generally, the relatively colder acidic digestion process using HCl and HNO3 in 3:1 (v/v), atmosphere inhibits the vertical convection of pollutants, and further quantification by an inductively coupled plasma while less precipitation reduces the amount of scavenging in mass spectrometer (ICP-MS). The instrument detection limit fall and winter. Therefore, the atmospheric TSP concentration (IDL) was defined as three times the standard deviation of was higher in the colder and dryer periods (Fig. 2). Notably, seven successive blank samples. The IDL of total As, As the amount of PM2.5 tended to be less affected by these two (III), and As (V) analyses were 0.0233, 0.00145, and 0.0261 environmental conditions than the amount of coarser ng/m3. The onsite blank samples (n = 2) contained 12.9 pg/m3 particles, since larger particles are mainly formed by surface As, 0.707 pg/m3 As (III), and 13.4 pg/m3 As (V), which accumulation, coalescence and agglomeration (Maricq et were all determined to be not detectable (ND) and to have al., 2002a, 2002b), which might be affected by rainfall and analytical purity. The quality assured blank samples were temperature. These environmental conditions will be discussed added to the analytical sequence every 10 sample injections, in more detail later in this work, with regard to their and all showed ND results. The standard solution containing relationships with the level of arsenic in the ambient air. an identified amount of As was used to check the reliability The atmospheric arsenic samples were collected with a of the calibration line every 10 to 15 samples during the high-volume air sampler (PS-1, Graseby Anderson, GA, ICP-MS analysis. The calibrated value should be ±10% of USA) and using the standard method (NIEA A102.12A) the prepared concentration, or the calibration line should be established by the Environmental Analysis Laboratory, updated to fit the instrument conditions. In this study, the Taiwan. The PS-1 sampling flow rate was controlled at 250– calibration line passed all the reliability tests.

Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013 935

250 50 600 d < 2.5 m 2.5 < d < 10 m ) 500 3 200 10 < d < 100 m 40 g/m

Temperature C)  Precipitation o 400 150 30

300 100 20 Temperature( 200 (mm) Precipitation

50 10

Suspended paticulate ( 100

0 0 0 Jan, 2011 Jan, 2011 Sep, 2011 Oct, 2012 Jan, Dec, 2011 Dec, Feb, 2011 Feb, 2012 Nov, 2011 Nov, Aug, 2011 Aug, July, 2011 July, May, 2011 May, 2012 May, June, 2011 June, 2012 June, April, 2011 April, April, 2012 2012 April, March, 2011 March, 2012 Fig. 2. Concentrations of particulate matters vs. various temperature conditions and precipitation.

The deposition fluxes were calculated in terms of dry RESULTS AND DISCUSSION and wet deposition. The modeled dry deposition flux was calculated by the following Eq. (1). Arsenic Deposition In this study, the arsenic concentrations in the atmosphere Fd = Cair × Vd (1) of eight sampling sites were pooled together, and the mean value thus derived represents the average atmospheric arsenic where Fd stands for the dry deposition flux; Cair represents level around Chiayi County in the period of January 2011 the measured As concentration in the ambient air, and Vd to June 2012. The As concentrations ranged from 2.40 to 6.24 3 means the dry velocity. The dry velocities (Vd) in this study ng/m , close to value found in previous studies (Glooschenko were taken from Fang et al. (2012), which utilized PM10 as and Arafat, 1988; Boamponsem et al., 2010; Sakata and an aerodynamic particle for the calculations in its As dry Asakura, 2011; Fang et al., 2012b). Fig. 3 shows the total deposition model (Fang et al., 2012b). (dry + wet) arsenic deposition flux in each month ranged from Three major components were first determined for the 65.0 to 473 μg/m2-month, with a mean of 192 μg/m2-month. wet deposition calculations, namely the atmospheric arsenic The seasonal flux variation was not significant, as there were concentration (Cair), particle scavenging ratio (Sp), and only two very high values, which occurred in November precipitation (P).The wet deposition flux could thus be 2011 and June 2012. According to the atmospheric arsenic derived using Eq. (2). concentration curve shown in Fig. 3, there were higher values in spring (February to April) and fall (September to Fw = Cair × Sp × P (2) November), similar to the trend found in previous studies (Sakata and Asakura, 2011; Shi et al., 2012). However, these In this equation, the scavenging ratio is defined as the As concentrations were not closely correlated to the total arsenic concentration dissolved in raindrops divided by the deposition fluxes, as seen in Fig. 3. Additionally, the partition concentration in the air during the precipitation, and this ratio of wet deposition (wet deposition flux/total deposition approach has been used to estimate the precipitation flux × 100%) was higher from May to August (63.6 to scavenging of aerosol trace components, sulfur and nitrogen 73.2% in mass), which had the similar partition result of oxides (Huang et al., 2011). Based on Eq. (2), a greater the major ionic components reported in the previous study concentration of atmospheric arsenic, scavenging ratio, and (Budhavant et al., 2012). The two different mechanisms of precipitation would increase the wet deposition flux of dry and wet deposition might be the reason why no clear total arsenic in the ambient air. In this study, the monthly seasonal effect was seen in the pooled deposition fluxes. As concentrations (Cair) were measured with a PS-1 sampler, Therefore, these two pathways are discussed separately in a while the precipitation data were collected from the Taiwan later section. Air Quality Monitoring Network (Taiwan Environmental Protection Administration, 2012). Additionally, the scavenging Seasonal Variation of Dry Deposition ratio (Sp) used in this study were based on those used in With regard to the dry deposition flux, the most Sakata et al. (2009), which focused on the seasonal variations influential factors were the wind velocity and the particulate of trace element wet deposition fluxes at sites along the concentration in the atmosphere (Sakata and Asakura, 2009). 2 coast of the Sea of Japan. Sp was thus set at 290 and 310 Dry deposition flux levels rose from 34.4 μg/m -month in for the wet and dry seasons, respectively. January to 152 μg/m2-month in April, then fell again to a low

936 Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013

500 10 Wet deposition flux ) 3 Dry deposition flux 87.6

-month) 400 2 Total arsenic concentration 8 76.7 g/m  300 6

200 66.1 73.3 71.4 73.2 63.6 4 100 69 33.4 23.2 23.6 47.1 28.1 31 concentrations, (ng/m Total arsenic 24.8 28 11.4 Total As Deposition Flux ( Total 6.9 0 2 Jan, 2011 Jan, Sep, 2011 Oct, 2011 2012 Jan, Dec, 2011Dec, Feb, 2011 Feb, 2012 Nov, 2011 Aug, 2011 July, 2011 May, 2011 May, 2012 June, 2011 June, 2012 April, 2011 April, 2012 March, 2011 March, 2012 Fig. 3. Total As deposition flux vs. concentration. of 41.3 μg/m2-month in June 2011, indicating the relatively PM concentrations were also evaluated, with r-values of high level of dry deposition in spring and low level in 0.9417 and 0.9347 for PM2.5 and PM10, respectively. These summer. Later on, the dry flux increased again to a high level high correlations are supported by the results of previous of 161 μg/m2-month in October 2011 then decreased to research that focuses on the temporal characteristics of 58.2 (μg/m2-month) in January 2012. In the spring of 2012, arsenic aerosol in urban area (Tsai et al., 2003). In addition, the same trend was observed as in 2011, with 139 μg/m2- the dry deposition fluxes were also significantly correlated 2 month in March and 72.95 μg/m -month in June. The average with both PM2.5 (p-value = 0.0036) and PM10 (p-value = dry deposition flux of arsenic was 84.47 μg/m2-month in 0.0012), although the correlations were weaker than those Chiayi County for the whole period examined in this study. between arsenic and PM levels. These results might be High dry deposition flux levels were found when there caused by various factors, such as variations in wing speed was low wind velocity, while low dry deposition flux levels and precipitation, which may have affected dry deposition were found with high wind velocity (Fig. 4.), supported by mechanism during period examined. the previous study (Fang et al., 2011). The highest wind The composition of total atmospheric arsenic was also speeds occurred in winter, especially in December and quantified in terms of As(III), As(V), and total arsenic, January, and the lowest was recorded in April, before rising since they have different toxicities [As(III) > AS(V)]. Table 2 again in June. More windy conditions might suspend the shows that the As(III) level ranged from 0.65 to 1.13 ng/m3 particles, while during quieter conditions the particles may in fall and went up to 1.19 and to 2.80 ng/m3. Meanwhile, be deposited from the atmosphere. Dry deposition contributes the As(V) concentrations ranged in 1.30–2.20 ng/m3 in fall, most to the total arsenic flux in the periods following the and increased to 3.25–5.56 ng/m3 in the following winter. months with high wind speeds. At high wind speeds more The data range found in this study is close to that reported particles are put into the atmosphere, and when the winds in a previous work that focused on atmospheric arsenic in reduce the particles are then easily get deposited. This is central Taiwan (Fang et al., 2012a). The results show that 3 supported by the high amount of PM2.5 (64.6 µg/m ) in the the composition of arsenic species in fall was dominated by 3 atmosphere in February 2011 and PM10 104 (µg/m ) in March As (V) in the range of 63.2 to 68.1 wt% (mean = 66.4 wt%), 2011, which followed the high wind speeds (and thus lower while this increased slightly to 63.0 to 82.4 wt% (mean = particle levels) recorded in January 2011 (3.22 m/s), as 68.9 wt%) in winter. The solubilities of As(V) and As(III) shown in Fig. 5. are 167 and 20 g/L, respectively, which supports the higher With regard to the PM2.5 and PM10 seasonal concentration mass fraction of As(V) being extracted out by wet scavenging. curves, the trends of arsenic concentration, dry deposition The results of the composition analysis also indicate that flux, and atmospheric PM level are very similar. In order to As(III) was more abundant in fall 2011 (33.6%) than in clarify the relationships among these, correlation calculations winter (31.1%), and thus the level of toxicity was also greater were carried out using the STATISTICA 10.0 (StatSof®, in fall 2011. 2012) statistical software, with the results shown in Table 1. The results show significant correlations between arsenic Precipitation and Deposition concentration and PM levels, while the p-values of PM2.5 Rainfall can wash out most of the pollutants in the and PM10 were both 0.00001 (< 0.01) at a 99% confidence atmosphere (Calvo et al., 2012) and thus also reduce the level. The highly linear correlations between arsenic and level of arsenic, and thus can be seen in the wet deposition

Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013 937

200 Dry deposition flux 3.5 7 a. Mean Wind Speed -month) 2 Total arsenic conc.

3.0 6 ) 3 g/m

 150

2.5 5 100

2.0 4

50 Mean Wind Speed (m/s) Wind Speed Mean

1.5 3 (ng/m conc. arsenic Total

0 1.0 2 Dry Deposition Flux of Total As ( Total Flux of Dry Deposition Sep, 2011 Oct, 2011 Jan, 2012 Jan, 2011 Dec, 2011 Dec, Feb, 2012 Feb, 2011 Nov, 2011 Aug, 2011 July, 2011 July, May, 2012 May, 2011 June, 2012 June, June, 2011 June, April, 2011 April, April, 2012 April, March, 2012 March, March, 2011 March, Fig. 4. Dry deposition flux of total As vs. wind speed and As concentration.

0.010 120 b. Total dry As conc. ) 3 PM conc. 10 ) 100 3 g/m 0.008 PM conc.  2.5 g/m  0.00624 80 0.006 60 0.004 40

0.002

20 ( concentration, dry PM Total As dry concentration ( concentration dry As Total

0.000 0 Sep, 2011 Sep, Oct, 2011 2012 Jan, Jan, 2011 Jan, Dec, 2011 Dec, Feb, 2012 Feb, Feb, 2011 Feb, Nov, 2011 Nov, Aug, 2011 Aug, July, 2011 May, 2012 May, May, 2011 May, June, 2012 June, June, 2011 June, April, 2011 April, April, 2012 April, 2012 March, 2012 March, March, 2011 March, Fig. 5. Total atmospheric As concentration vs. suspended particle levels in the ambient air around Chiayi County.

Table 1. The correlations among As concentration, dry deposition flux and PM levels in the atmosphere. PM PM Arsenic levels 2.5 10 r-value p-value r-value p-value As conc. 0.9417 0.00001 0.9347 0.00001 As dry deposition flux 0.6489 0.0036 0.7008 0.0012 fluxes calculated in the current study. Fig. 6 shows the highest seasonal changes in wet deposition flux were not observed wet deposition flux of arsenic was in June 2012, with the in this study, in contrast to the findings of a previous work value of 414 μg/m2-month, while the amount of precipitation (Sakata and Asakura, 2009). According to the calculation at this time 415 mm. Additionally, the lowest value was of wet deposition, as shown in Eq. (2), the flux was affected recorded in April 2011, with the arsenic wet deposition flux by the scavenging ratio, precipitation, and concentration, value and the precipitation being 11.3 μg/m2-month and 11.3 with the scavenging ratio in both warm and cold seasons set mm, respectively. The average value for wet deposition over as constants in this study. The seasonal trends of the other the whole period studied was 108 μg/m2-month. Additionally, two factors are also shown in Fig. 6, indicating very similar

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Table 2. Chemical composition of the atmospheric dry arsenic concentration in fall and winter. October (Fall) in 2011 February (Winter) in 2012 Sample site As (III) As (V) Total As As (III) As (V) Total As (ng/m3) (ng/m3) (ng/m3) (ng/m3) (ng/m3) (ng/m3) A. 1.13 2.20 3.33 2.80 4.76 7.56 B. 1.01 1.73 2.74 1.19 5.56 6.74 C. 0.79 1.69 2.48 2.41 5.14 7.55 D. 0.79 1.63 2.42 1.88 3.97 5.85 E. 0.77 1.53 2.3 1.54 3.28 4.82 F. 0.65 1.30 1.95 1.69 3.25 4.94 G. 0.69 1.43 2.12 1.67 3.41 5.09 H 0.86 1.72 2.58 2.05 4.26 6.31 Mean 0.84 1.65 2.49 1.90 4.21 6.11 RSD 19.3 16.2 16.9 26.9 21.0 18.3

500 Wet deposition flux 600 10 a. Precipitation -month) 2 500

Total arsenic conc. )

400 3 g/m

 8 400 300 300 6 200 200 Precipitation (mm) 4

100 (ng/m conc. arsenic Total 100

0 0 2 Wet Deposition Flux of Total As ( As of Total Flux Wet Deposition Jan, 2012 Jan, 2011 Sep, 2011 Oct, 2011 Dec, 2011 Feb, 2012 Feb, 2011 Nov, 2011 Aug, 2011 July, 2011 May, 2012 May, 2011 June, 2012 June, 2011 April, 2011 April, 2012 March, 2012 March, 2011 Fig. 6. Wet deposition flux of total As vs. precipitation and As concentration. trends for both precipitation and wet deposition flux. With GIS 3.3, was used to obtain the As distributions. Data for regard to the statistical analyses results shown in Figs. 7(a) the arsenic concentrations at eight sampling sites in and 7(b), a significant linear correlation was found between October, 2011 were obtained, because higher levels of air precipitation and wet deposition flux (p-value = 0.0000002; pollutants are generally found in dry and cold seasons, and r-value = 0.9306). Sakata and Asakura (2009) reported that this was also true in the current work. In Fig. 8, the main the As wet deposition flux had the same trend as its wind direction in northern Chiayi was from the northwest atmospheric concentration for the period 2003 to 2005, (recorded at the Xingang site), and arsenic levels were also along with significant seasonal variations; however, the As monitored in the north-east (in Puzi site) and west north- concentration was not a dominant factor with regard to wet west (at the Chiayi City site) downwind of areas with heavy deposition (p-value = 0.1077) in the current study. Comparing industrial and human activity. For the first transport pathway the amount of precipitation in the sampling period examined from sites A (3.33 ng/m3) to H (2.58 ng/m3), C (2.48 ng/m3) in this study and the one in Sakata and Asakura (2009), a and G (2.12 ng/m3), the As concentration reduced along relatively high value was found (521 mm) in this work with the wind direction. This indicates that the Jiatai and compared to the earlier one (< 450 mm). The wet deposition Puzi industrial parks did not make significant contributions trends found in the current study were thus also significantly to the As concentration, even in their local areas, because affected by the precipitation, rather than only by the arsenic the major industries in these parks are metal processing, concentration. polymer production, and food production, instead the ones that produce a lot of As, such as copper smelting and solid GIS Spatial Distribution of Atmospheric Arsenic waste incineration. The same trend was found in another Concentration pollutant transport path, from sites A (3.33 ng/m3) to B (2.74 To analyze the level of arsenic in the ambient air around ng/m3) and E (2.30 ng/m3), indicating that Minsyong and Chiayi County, a geographical information system, Arc View Touciao industrial parks and Chiayi City did not have any

Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013 939

a. r = -0.3919, p = 0.1077 6.5

6.0 -month

3 5.5

g/m 5.0 

4.5

4.0

3.5

3.0

2.5

Wet As deposition flux, 2.0 -50 0 50 100 150 200 250 300 350 400 450 3 Total As concentration, g/m b. r = 0.9306, p = 0.0000002 600

500 -month 3 400 g/m 

300

200

100

Wet As deposition flux, -100 -50 0 50 100 150 200 250 300 350 400 450 Precipitation, mm Fig. 7. (a) Correlation analyses of wet As deposition flux vs. As concentration; (b) correlation analyses of wet As deposition flux vs. precipitation. significant effects on the As concentration. Based on the 3. The correlations between the atmospheric arsenic As concentration distribution in the dry season, the main concentration and PM levels were significant, while contribution to atmospheric As was mid-term transport from the p-values of PM2.5 and PM10 were both 0.00001 the north of Chiayi County, instead of local emissions. (< 0.01) at a 99% confidence level. Highly linear correlation between arsenic and PM concentrations CONCLUSIONS were also evaluated by r-values equal to 0.9417 and 0.9347 for PM2.5 and PM10, respectively. 1. The total (dry + wet) arsenic deposition flux of each 4. The composition of arsenic species in fall were dominated month ranged from 65.0 to 473 μg/m2-month, with a by As (V), with the ranged of 63.2 to 68.1 wt% (mean mean of 192 μg/m2-month in Chiayi County. The = 66.4%), while this slightly increased to a ranger of seasonal variation of total As deposition flux was not 63.0 to 82.4% (mean = 68.9%) in winter. significant, and this was because two different 5. The average value for wet deposition was 108 μg/m2- mechanisms (dry deposition and wet scavenging) were month, while the highest value of 414 μg/m2-month pooled together in this work. was found in the wet season, and the lowest value of 2. The average dry deposition flux of arsenic was 84.5 11.3 μg/m2-month in the dry season. A significant linear μg/m2-month in Chiayi County, while the seasonal correlation between precipitation and wet As deposition variation ranged from 34 μg/m2-month (wet season) to flux was found (p-value = 0.0000002; r-value = 0.9306), 161 μg/m2-month (dry season). Additionally, the dry and the As concentration was not a dominant factor deposition flux had the opposite trend to the wind speed. with regard to the wet deposition (p-value = 0.1077).

940 Lin et al., Aerosol and Air Quality Research, 13: 932–942, 2013

Fig. 8. Contour diagram of total dry arsenic concentration.

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