10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Submicron Aerosol at a Receptor Site in New Delhi: Interpreting Sources and Their Origin
SAHIL BHANDARI, Shahzad Gani, Dongyu S. Wang, Kanan Patel, Sarah Seraj, Prashant Soni, Zainab Arub, Gazala Habib, Joshua Apte, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 1593 Working Group: Source Apportionment
Abstract Delhi, India is the second most populous agglomeration in the world. High annual average PM1 concentrations of about 50 µg m-3 and frequent severe pollution episodes, particularly in winters with concentrations as high as 500 µg m-3, contribute significantly to acute and chronic PM exposure. As a part of the Delhi Aerosol Supersite (DAS) campaign, speciated submicron measurements at 1 minute time resolution have been collected from January 2017 to present at the Indian Institute of Technology Delhi using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and an Aethalometer. Here we report the results of detailed source apportionment analysis conducted on 1.5 years of ACSM mass spectral data using positive matrix factorization (PMF). For non-refractory organics, oxidized organic aerosol (OOA) is the most important factor, contributing about 50% in all seasons. A combined organic-inorganic mass spectral (MS) PMF analyses attributes chloride almost completely to ammonium chloride. This ammonium chloride factor concentrations drop systematically from winter to summer, consistent with its volatile nature. BBOA factors indicate multiple biomass burning events that have been captured during the course of the campaign. Several episodic events associated with substantially higher concentrations compared to seasonal averages, including winter chloride concentrations of about 150 µg m-3 have also been detected. Heavy rainfall and monsoon events are associated with a large drop in hydrocarbon-like organic aerosol (HOA) and OOA concentrations and a complete absence of BBOA. PMF results show that OOA time series correlated well with nitrate (NO3-) and sulfate (SO42-), and that HOA time series correlated well with concentrations of carbon monoxide (CO) and nitrogen oxides (NOx) from nearby monitoring stations. We compare our PMF apportionment of BC to simpler fossil fuel and biomass burning source apportionment techniques relying strictly on Aethalometer measurements of wavelength-dependent light absorption, such as the Sandradewi et al (2008) model. Back trajectory analyses in HYSPLIT have been combined with factor and species concentrations to generate probability distribution contribution function (PSCF) and conditional probability function (CPF) rose plots identifying the local and regional nature of respective sources. These source apportionment results for Delhi can help in the development of targeted policy actions for reducing fine PM concentrations in this polluted megacity.
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