10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Investigation of Organic Aerosol in Delhi, India, using an Extractive Electrospray Ionization Time-of-Flight Mass Spectrometer (EESI-LTOF)
Varun Kumar, Deepika Bhattu, Yandong Tong, Veronika Pospisilova, Giulia Stefenelli, Amelie Bertrand, Roberto Cassotto, Rangu Venkata Satish, Pawan Vats, Urs Baltensperger, Dilip Ganguly, Neeraj Rastogi, S.N. Tripathi, Andre S.H. Prévôt, JAY G. SLOWIK, Paul Scherrer Institute
Abstract Number: 1499 Working Group: Air Quality in Megacities: from Sources to Control
Abstract The densely populated Indo-Gangetic Plain is subject to extremely high particulate matter (PM) concentrations during winter, which significantly affect radiative forcing, increase mortality rates, and cause other deleterious effects on human health. Pollution reduction efforts are hindered by the lack of consensus on the dominant factors governing PM concentrations, particularly the relative importance of specific sources, primary vs. secondary aerosol, and secondary aerosol formation pathways. In particular, investigation of secondary organic aerosol (SOA) sources and formation processes has traditionally been hindered by the reliance of conventional online instrumentation on thermal desorption and/or hard ionization, which destroys much of the chemical information needed for source and process identification. The recently developed extractive electrospray ionization long-time-of-flight mass spectrometer (EESI-LTOF) overcomes these obstacles by continuous sampling of aerosol into a spray of charged droplets (100 ppm NaI in 50:50 water/acetonitrile) generated by a conventional electrospray probe. Soluble components are extracted, the droplets are gently evaporated, and the intact organic molecules are detected as charged adducts with Na+, with the observed signal proportional to mass concentration. Here we use the EESI-LTOF to investigate SOA sources and formation processes in the Indian capital city of New Delhi during a field campaign from January to March, 2018.
New Delhi is home to nearly 19 million people and routinely experiences very poor air quality during the winter due to a combination of a low boundary layer and emissions from a complex array of sources, including vehicle traffic, domestic wood and coal heating, cooking emissions, and uncontrolled combustion activities (e.g. trash burning). The EESI-LTOF was deployed on the campus of the Indian Institute of Technology Delhi, an urban background site approximately 10 km south of the city center. Supporting instrumentation onsite included an Aerodyne high resolution long-time-of-flight aerosol mass spectrometer (L-ToF-AMS), as well as measurements of organic gases (by proton transfer reaction mass spectrometry), trace elements, and optical absorption. SOA sources and formation are characterized by investigation of process-specific tracer ions in the EESI-LTOF mass spectra identified in previous chamber and field campaigns, as well as by positive matrix factorization (PMF) utilizing the Source Finder (SoFi) interface for the multilinear engine (ME-2). We assess the importance of the major secondary sources governing SOA formation, their likely formation pathways, and implications for optical and health-related properties.