AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Sources and Dynamics of the Submicron Aerosol in Delhi, India: Overview of the 2017 Delhi Aerosol Supersite Campaign
Joshua Apte, Shahzad Gani, Sahil Bhandari, Sarah Seraj, Dongyu S. Wang, Zainab Arub, Gazala Habib, LEA HILDEBRANDT RUIZ, University of Texas at Austin
Abstract Number: 592 Working Group: Urban Aerosols
Abstract Delhi consistently ranks as one of the most polluted megacities in the world, where annual average PM2.5 levels exceed 130 µg m-3 , and wintertime episodes commonly reach 500 µg m-3 or higher. While Delhi’s pollution has attracted international attention, understanding of the sources and atmospheric dynamics of high aerosol concentrations is still incomplete. To address these data gaps, we established a supersite to characterize the chemical composition of the ambient submicron aerosol at the Indian Institute of Technology, Delhi. Continuous online measurements of aerosol composition have been collected since January 2017, including nonrefractory PM1 (NR-PM1, via an Aerodyne aerosol chemical speciation monitor), black carbon (BC, via aethalometer) and particle size distributions (scanning mobility particle sizer).
This overview presentation summarizes the key scientific findings of the Delhi Aerosol Supersite campaign to date. We observe marked seasonal and diurnal variability in the concentration and composition of PM1 owing to the interactions of sources and atmospheric mixing. Nocturnal concentrations of some primary species routinely exceeded daytime levels by factors of 3-5. Winter nights had unusually large particles (count median diameter ~ 100-120 nm) and high PM1 mass loadings (150-200 µg m-3), with concentrations dropping and particles shrinking in warmer months. Biomass burning and traffic are likely major sources for BC, for which concentrations exhibit twin evening and morning peaks exceeding 30 µg m-3 in winter months. A pronounced and recurring early morning peak of PM1 chloride (~20-30 µg m-3) may reveal a previously unappreciated emissions source in Delhi. Diurnal variation was less pronounced for sulfate, nitrate, and ammonium species (mass loadings ~10-20 µg m-3), implying that these species may also have strong regional sources surrounding Delhi. As observed elsewhere, organic species dominated NR-PM1 and exhibited sharp diurnal variability.