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of developing and emerging countries in Southeast Asia, in which rapid urbanization, vehicles of obsolete technology, outdated air quality legislations, and crumbling infrastructure lead to poor air quality.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.
Highlights
Megacities in less developed regions continue to suffer from high levels of air pollution and its consequences as a result of rapid urbanization and economic growth (WHO, 2016)
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 Black carbon (BC)
The highest mean equivalent BC (eBC) mass concentration and variability were observed at TAFT RS (25.7 ± 17.2 μg m–3) while the lowest mean was measured at Manila Observatory (MO) urban background station (UBS) (6.9 ± 4.9 μg m–3)
Summary
Megacities (cities with more than 10 million people) in less developed regions continue to suffer from high levels of air pollution and its consequences as a result of rapid urbanization and economic growth (WHO, 2016). This study focuses on following objectives: 1) to determine the spatial and diurnal variability of equivalent BC (eBC, a proxy for soot; a nomenclature suggested by Petzold et al, 2013 when describing BC measured optically), 2) to determine the factors that drive these variabilities, 3) to estimate the contribution of local traffic emissions to ambient air quality, and 4) to compare the observed eBC mass concentrations in Metro Manila with other cities, and 5) to validate models of spatial distribution of eBC mass concentration. From the particle light absorption coefficient, the eBC mass concentration is calculated, using a default mass absorption cross section of 6.6 m2 g–1 (Petzold and Schonlinner, 2004) For this campaign, TROPOS has modified the flow rate of the MAAP from 16 L min–1 to 3 L min–1 to avoid filter loading, when measuring at highly polluted sites (Hyvärinen et al, 2013). The result is one spatial plot showing the average of all the mobile runs with high spatial resolution
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