10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Source Apportionment of Absorbing Aerosols (Soot Particles) in Delhi, India during a Highly Polluted Period (Wintertime)
SURESH TIWARI, Rajan K. Chakrabarty, Umesh C. Dumka, Atul K. Srivastava, Deewan S. Bisht, Philip K. Hopke, Indian Institute of Tropical Meteorology
Abstract Number: 134 Working Group: Air Quality in Megacities: from Sources to Control
Abstract Urban areas in the developing countries are major sources of carbonaceous aerosols requiring detailed assessment of the concentrations and source apportionment in order to attain improved air quality. A seven-wavelength Aethalometer (Magee Scientific model AE-33) was utilized to measure the spectral absorption coefficient (babs) at 7 wavelengths and estimate Black Carbon (BC) mass concentrations in Delhi during a winter research campaign (December 2015 – February 2016). The Aethalometer measurements were supported by measurements of PM10 and PM2.5 concentrations and air-pollution gases (NOx, CO, and O3) as well as by Photoacoustic Extinctiometer (PAX) measurements of scattering, absorption coefficients, and single scattering albedo (SSA). From the measured babs, the Angstrom Aerosol Exponents (AAE) was estimated at 370, 470, 880, and 950 nm. Assuming values of AAE=1.0 and AAE=1.8 for the fossil-fuel combustion and biomass burning particles, respectively, the BC components (BCff and BCbb) were estimated via the “Aethalometer model”. Very high PM10 (246 ± 110 µg m-3) and PM2.5 (146 ± 70 µg m-3) concentrations were measured during the campaign period. BC represented a large fraction of the PM mass (9.8% to PM10 and 16.5% to PM2.5). The BC concentrations varied from 3.2 to 59.9 µg m-3 (mean of 24 ± 12 µg m-3) depending strongly on meteorological conditions i.e., changes in mixing layer height and dispersion, and on the differences in carbonaceous emission rates. The highest BC concentrations were observed during the nighttime and early morning hours. Fossil-fuel BC (BCff) was emitted by traffic, industrial sources, and domestic use of natural gas. Combustion of wood, waste material, dung cakes, and agricultural crop residue burning produced the BCbb. The highest contributions of BCff to BC were found during late-night hours and in the early morning (~03:00-08:00 hrs Local Standard Time: LST). On some days, high BCff was found until noon (~13:00 hrs LST). Large contributions of the BCbb to total BC were found during the early evening-to-night hours (~18:00 – 24:00 hrs LST) likely from increased domestic biofuel burning for cooking and heating as well as open fires in the roads during the cold winter nights. BCff and BCbb were strongly related to CO and NO emissions indicating common local primary combustion emissions. In general, higher BCff/BCbb values were associated with lower SSA values. A sensitivity analysis was performed to assess the BC source apportionment (i.e., BCff/BC and BCbb/BC) by changing the wavelength pairs and the AAEff and AAEbb values. The results showed that the “Aethalometer model” was more sensitive to changes in AAEff compared to AAEbb values. Although both sources of BC are important, biomass burning continues to deteriorate local air quality within and around urban environments in India and necessitates appropriate measures to mitigate the effects of BC on climate, ecosystems, and human health.