AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Primary and Secondary Sources of PM2.5 in the Kathmandu Valley, Nepal
MD ROBIUL ISLAM, Thilina Jayarathne, Ashley Gilbert, Maheswar Rupakheti, Elizabeth Stone, University of Iowa
Abstract Number: 384 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Kathmandu Valley, the capital region of Nepal, suffers from severe particulate matter (PM) pollution. In this study, we use molecular markers to identify and quantify sources of organic carbon (OC) in ambient PM2.5. Recent efforts in the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) focused on characterizing emissions from different under sampled but locally important sources such as garbage burning, varieties of cooking stoves, agricultural pumps, brick kilns with traditional technologies, etc. To evaluate the contributions of these and other sources to PM2.5, samples were collected at Bode site in the Kathmandu Valley during April 11-24, 2015. The daily average PM2.5 concentrations varied between 30 µg/m3 and 207 µg/m3, which are 1.2 - 8.3 times the World Health Organization (WHO) 24 hour guideline of 25 µg/m3. PM2.5 was comprised in part by water-soluble ions, including sulfate (16%), ammonium (9%), nitrate (4%), indicating secondary inorganic aerosol contribution, as well as calcium (1.2%) and magnesium (0.1%), reflecting airborne soil dust. Major fractions of PM2.5 were OC (27 ± 8%) and elemental carbon (13 ± 7%). To gain insight to sources of OC, gas chromatography coupled to mass spectrometry (GCMS) was used to quantify primary and secondary source molecular markers. Some well-established molecular markers identified and quantified in this study were levoglucosan (1230 ± 1153 ng/m3), 1,3,5-triphynylbenzene (0.8 ± 0.5 ng/m3), cholesterol (3.0 ± 6.7 ng/m3), stigmastanol (1.4 ± 6.7 ng/m3), and cis-pinonic acid (4.5 ± 0.6 ng/m3) indicating contributions from biomass burning, garbage burning, food cooking, cow-dung burning, and monoterpene secondary organic aerosols, respectively. Chemical mass balance source apportionment modeling will be used to quantitatively estimate source contributions to OC. Incorporation of newly characterized source profiles will enable us to apportion a larger fraction of OC to a wider number of sources.