Spatial Characterization of Black Carbon Mass Concentration in the Atmosphere of a Southeast Asian Megacity: an Air Quality Case Study for Metro Manila, Philippines
Total Page:16
File Type:pdf, Size:1020Kb
Aerosol and Air Quality Research, 18: 2301–2317, 2018 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2017.08.0281 Spatial Characterization of Black Carbon Mass Concentration in the Atmosphere of a Southeast Asian Megacity: An Air Quality Case Study for Metro Manila, Philippines Honey Dawn Alas1,2*, Thomas Müller1, Wolfram Birmili1,6, Simonas Kecorius1, Maria Obiminda Cambaliza2,3, James Bernard B. Simpas2,3, Mylene Cayetano4, Kay Weinhold1, Edgar Vallar5, Maria Cecilia Galvez5, Alfred Wiedensohler1 1 Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany 2 The Manila Observatory, Quezon City 1101, Philippines 3 Department of Physics, Ateneo de Manila University, Quezon City 1108, Philippines 4 Institute of Environmental Science and Meteorology, University of the Philippines, Quezon City 1101, Philippines 5 Applied Research for Community, Health and Environment Resilience and Sustainability (ARCHERS), De La Salle University, Manila 1004, Philippines 6 Federal Environment Agency, 14195 Berlin, Germany ABSTRACT Black carbon (BC) particles have gathered worldwide attention due to their impacts on climate and adverse health effects on humans in heavily polluted environments. Such is the case in megacities of developing and emerging countries in Southeast Asia, in which rapid urbanization, vehicles of obsolete technology, outdated air quality legislations, and crumbling infrastructure lead to poor air quality. However, since measurements of BC are generally not mandatory, its spatial and temporal characteristics, especially in developing megacities, are poorly understood. To raise awareness on the urgency of monitoring and mitigating the air quality crises in megacities, we present the results of the first intensive characterization experiment in Metro Manila, Philippines, focusing on the spatial and diurnal variability of equivalent BC (eBC). The average mass concentration of eBC at the urban background station (UBS) was 7.0 ± 4.8 µg m–3 while at roadside (RS), hourly concentrations reached maximum values of 138 µg m–3, levels that are significantly higher than in European cities. At RS, the diurnal cycles of eBC mass concentration were connected most strongly with traffic dynamics and street configuration, while a notable influence of planetary boundary layer evolution was observed in the UBS. Results of mobile measurements conducted multiple times along two fixed routes showed high spatial variability ranging from 3–80 µg m–3 within a 500-m radius. Alarmingly, the highest concentrations were found in the most crowded areas where people spend more than eight hours a day. Keywords: Black carbon; Megacity; Spatial and diurnal variability; Mobile measurements. INTRODUCTION (BC) particles - nanoparticles that carry toxic materials (Nemmar et al., 2002; WHO, 2012) which are linked to Megacities (cities with more than 10 million people) in various diseases (Krzyzanowski et al., 2005; WHO, 2007; less developed regions continue to suffer from high levels HEI, 2010) - remain unregulated (Krzyzanowski and Cohen, of air pollution and its consequences as a result of rapid 2008). Despite growing efforts to monitor BC in fixed urbanization and economic growth (WHO, 2016). Criteria locations, it is still extremely challenging to model its spatial pollutants (gaseous and particulate matter or PM) are being distribution and estimate personal exposure levels in a monitored and regulated according to WHO guidelines microscale since BC is highly variable in space and time (WHO, 2006) in these megacities. However, black carbon (Peters et al., 2013; Rakowska et al., 2014). In recent years, atmospheric researchers have started to shift their attention from stationary monitoring towards mobile pollutant measurements. Mobile measurements are *Corresponding author. able to capture features of the considerable spatial variability Tel.: +49 341 2717 7060; Fax: +49 341 2717 99 7060 of pollutant concentrations typically found in urban E-mail address: [email protected] atmospheres. On the technical side, mobile measurements 2302 Alas et al., Aerosol and Air Quality Research, 18: 2301–2317, 2018 require robust and portable devices that are typically mounted Hopke et al. (2008) reported that in terms of elemental on mobile platforms such as backpacks of pedestrians, black carbon (the black carbon content of the fine fraction bicycles, and vehicles. High time resolution, in the order of filters was measured using a reflected light instrument), seconds or minutes, is required to detect spatial gradients of Metro Manila has the second highest concentration in Asia, pollutant concentrations across selected itineraries. This next to Dhaka, Bangladesh. Clearly, the current criteria does method has been proven useful in different scientific not provide enough information on the air quality situation applications such as evaluating representativeness of fixed in Metro Manila, and possibly in other megacities. stations (Nerriere et al., 2005), determining emission factors To address this, the Metro Manila Aerosol Characterization (Karjalainen et al., 2014; Jezek et al., 2015), and developing Experiment (MACE 2015) was initiated. This was the first land use regression models (Ruths et al., 2014; Ghassoun intensive monitoring of air pollution in Metro Manila, et al., 2015). More importantly, it can increase the accuracy conducted in the summer of 2015. The general objective of in estimating personal exposure to pollutants (Adams et al., the pilot case study was to investigate the diurnal and 2002; Birmili et al., 2013; Peters et al., 2014; Patton et al., spatial characteristics of black carbon in the megacity 2016; Williams and Knibbs, 2016). Furthermore, the high- Manila. MACE 2015 also aimed to provide evidence on resolution data of mobile platforms is effective in validating the need to update and improve existing air quality policies, modelled spatial distribution of pollution (Dons et al., 2014). and to suggest BC as a more suitable criterion for roadside We note that most mobile measurement campaigns have emissions, since it can provide a deeper understanding of the been conducted in European cities (Schneider et al., 2008; health impacts of air pollution more than PM10 and PM2.5. Dons et al., 2011, 2012; Birmili et al., 2013; Dons et al., Specifically, this study focuses on following objectives: 2013; Van Poppel et al., 2013; Peters et al., 2014; Van den 1) to determine the spatial and diurnal variability of equivalent Bossche et al., 2015, 2016) and North America (Westerdahl BC (eBC, a proxy for soot; a nomenclature suggested by et al., 2005; Fruin et al., 2008; Westerdahl et al., 2008; Petzold et al., 2013 when describing BC measured optically), Zhu et al., 2008; Levy et al., 2014; Baldwin et al., 2015). 2) to determine the factors that drive these variabilities, 3) To date, there is a notable lack of representative data on to estimate the contribution of local traffic emissions to the spatial distribution of BC in developing and emerging ambient air quality, and 4) to compare the observed eBC countries (Hung et al., 2014; Rakowska et al., 2014; Kim et mass concentrations in Metro Manila with other cities, and al., 2015). The air quality situation in megacities of those 5) to validate models of spatial distribution of eBC mass countries is often precarious, because pollutant sources and concentration. populations intermingle in a dense fashion on limited space. To achieve these objectives, eBC mass concentrations Moreover, there tend to be more complex street configurations, were measured at three sites, at two roadside sites and at an outdated vehicle fleet, intense industrial emissions, less urban background station. The influence of meteorology, stringent regulations, and consequently, more people at risk. traffic schemes, and street topography were investigated. An example is the megacity of Metro Manila in the Mobile measurements were performed along two fixed routes Philippines. Metro Manila is home to 12 million people which covered different microenvironments and exposure and has a population density of 21 thousand people per scenarios. Background correction was also performed to square kilometre (Philippine Statistics Authority, 2016). determine the contribution of local traffic sources to urban Consequently, it has the highest number of registered air quality. Results from this study can raise awareness on motor vehicles compared with other cities in the country, the current air quality situations that developing and with a reported number of 2.2 million (Philippine Land emerging megacities experience, potentially influence the Transportation Office, 2015). With these statistics, it is not air quality policies, and help increase the accuracy of surprising that 90% of emissions in this city is from mobile environmental and health studies in these regions. sources (Environmental Management Bureau, 2012). Due to its unique topography (Manila Bay on its West and the EXPERIMENT DESIGN Laguna Lake on the East), the air quality of Metro Manila is mainly urban-originated and the influence of long-range- The measurements were performed in the highly urbanized transported aerosol is minimal (Kim Oanh et al., 2006). In megacity of Metro Manila, the country’s National Capital 1999, the Clean Air Act was established to improve air Region (NCR) that is an agglomerate of 17 local quality. Under this law, the limits were set for criteria government units. The climate of the region can be