AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Submicron Aerosol during Autumn 2018 in the Most Polluted Megacity: The Delhi Aerosol Supersite Study (DAS)
KANAN PATEL, Sahil Bhandari, Shahzad Gani, Purushottam Kumar, Gazala Habib, Joshua Apte, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 272 Working Group: Urban Aerosols
Abstract New Delhi, India is the most polluted megacity in the world and routinely experiences high aerosol concentrations. In particular, the autumn season (mid Sep-Nov) experiences some of the highest concentrations which has been hypothesized to be due to agricultural burning of the “kharif” crops in the Indo-Gangetic plains, and transitional meteorology (between monsoon and winter) during this period. As part of the Delhi Aerosol Supersite Study, NR-PM1 concentrations and composition have been measured using an Aerosol Chemical Speciation Monitor (ACSM) from January-2017 to present which includes autumn 2018.
In autumn 2018, the average NR-PM1 concentration increased from ~55 µg/m3 in the last two weeks of September to ~210 µg/m3 in November-2018. On November 5 (around the time of the festival of Diwali), the NR-PM1 concentration reached ~1100 μg/m3, highest in the 26 months of data collection.On average, organic aerosol (OA) constituted 68.7% while the inorganics, sulfate, nitrate, ammonium and chloride constituted 12.4%, 8.6%, 8.7% and 1.6% of NR-PM1 respectively during this season.
We performed source apportionment by using Positive Matrix Factorization on the OA data measured by the ACSM. Three factors—HOA (Hydrocarbon–like-OA), BBOA (Biomass-Burning-OA) and OOA (Oxidized-OA) were resolved. While BBOA dominated during episodic events, on average, all the factors contributed comparably (OOA–37%, BBOA–33% and HOA–30%), indicating equal importance of traffic (HOA), biomass-burning (BBOA) and secondary OA (OOA) during this season. Additionally, ~70% of 95th percentile BBOA concentration events during this season were associated with N and N-W wind directions, pointing towards the role of agricultural burning from the N-W states of Punjab and Haryana. Thus, our analysis provides insights into sources that influence submicron aerosol concentrations during an extremely polluted season in Delhi.