Within-City Variability of Ultrafine and Fine Particulate Matter in South Asian and North American Cities
PROVAT SAHA, Tanbhir Shovon, Dipika Roy Prapti, Albert Presto, Allen Robinson,
Bangladesh University of Engineering and Technology Abstract Number: 651
Working Group: Urban Aerosols
AbstractIn this study, we investigated the within-city variability of fine particle mass (PM2.5) and ultrafine particle number concentration (PNC) in Dhaka, Bangladesh, and Pittsburgh, USA, two cities with vastly different pollution sources and levels. We collected spatially dense co-measurements of PNC and PM2.5 at a wide range of sites spanning a variety of urban land use attributes (35 sites in Dhaka and 30 sites in Pittsburgh). We found that PNC levels exhibited a 3-4-fold variability between sites in each city, ranging from 20,000-100,000 # cm-3 in Dhaka and 7,000-28,000 # cm-3 in Pittsburgh. PM2.5 levels varied within 50% of the urban background level, ranging from 80-110 µg m-3 in Dhaka and 6-12 µg m-3 in Pittsburgh. We observed a moderate level of spatial correlation between PNC and PM2.5 measurements in both cities (R2 0.3 in Dhaka, and 0.4 in Pittsburgh), and consistent within-city spatial patterns in different seasons. Compared to the Pittsburgh levels, both PNC and PM2.5 levels in Dhaka were significantly higher, however, on a relative basis, PM2.5 was disproportionately higher (10-12 times higher) than PNC (3-4 times higher). The slope of PNC versus PM2.5 varied significantly between the two cities, suggesting that the sources and size distribution of particles that make up the majority of the PM2.5 mass were different in the two cities. Disproportionately higher PM2.5 levels in Dhaka are dominantly influenced by solid fuel combustion, including solid biomass burning, waste burning, and soil dust, which have a greater impact on particle mass concentration due to their larger size. In Pittsburgh, traffic (gasoline and diesel combustion) particles, relatively smaller in size compared to solid fuel combustion particles, likely play a dominant role in determining the within-city variability of PNC and PM2.5 mass.