AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Air Mass Characterization for the Megacity Delhi: Impacts on Aerosol Hygroscopicity and CCN Prediction
ZAINAB ARUB, Sahil Bhandari, Shahzad Gani, Prashant Soni, Joshua Apte, Lea Hildebrandt Ruiz, Gazala Habib, Indian Institute of Technology Delhi
Abstract Number: 415 Working Group: Aerosols, Clouds and Climate
Abstract Delhi is a highly polluted megacity influenced by anthropogenic emissions, and this work provides long term, real-time estimates of hygroscopicity parameter (к) and CCN. Aerosol composition and size distribution were conducted using ACSM and SMPS respectively at Delhi Aerosol Supersite (DAS) from January, 2017- March, 2018. The 5-days back trajectory revealed three distinct pathways originating from Arabian Sea (AS), Bay of Bengal (BOB) and North-West (NW) regions. The three air masses exhibited distinct characteristics of speciated non-refractory PM1(NR-PM1) and size distributions. The NW branch was the most anthropogenically influenced with high organic content and chloride compared to the others. Between the other two, BOB branch was more contaminated than AS branch with a relatively higher organic fraction and nitrate. The average к was approximately 0.3 for all the air masses (0.33±0.06, 0.31±0.06, 0.29±0.06), with strong diurnal variation. The total number concentration, as well as separately for Aitken and Accumulation modes were higher for the air masses originated from NW, followed by BOB and lastly the AS. The predicted CCN concentration and activated fraction (0.7-0.5 at 0.4% SS) for all supersaturations (0.1, 0.4, 0.8) also exhibited the same pattern for the three air masses as for the total number concentration. The CCN concentration showed a more prominent diurnal variation for the north-west compared to other two. On an overall basis, the estimated CCN and activated fractions were higher compared to all Indian measurement sites, which is expected owing to the high pollution occurring both locally and also as transported regionally by the different air masses. The in-depth hygroscopicity measurements are required to make CCN closures accurate and with the knowledge of CCN, cloud droplet number concentration can be better quantified and precipitation by GCMs better understood.