A203-02
Source apportionment of regional aerosols and spatial variability from The 2nd Nepal Ambient Measurement and Source Testing Experiment [NAMaSTE]-2 in the Kathmandu valley, Nepal

Tuesday, 15 December 2020: 17:36
Virtual
Benjamin Werden1, Michael Giordano2, Khadak Mahata3, James Douglas Goetz4, Erin Katz1, Prakash Bhave5, Puppala S Praveen5, Robert J Yokelson6, Elizabeth A. Stone7, Arnico K Panday8 and Peter DeCarlo9, (1)Drexel University, Philadelphia, PA, United States, (2)CNRS, Paris Cedex 16, France, (3)Institute for Advanced Sustainability Studies (IASS), Potsdam, Germany, (4)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (5)International Centre for Integrated Mountain Development, Kathmandu, Nepal, (6)University of Montana, Department of Chemistry, Missoula, MT, United States, (7)University of Iowa, Iowa City, IA, United States, (8)International Center for Integrated Mountain Development, Kathmandu, Nepal, (9)Johns Hopkins University, Department of Environmental Health and Engineering, Balitmore, MD, United States
Recorded Presentation
Abstract:
Kathmandu, Nepal is an urban basin home to over 3 Million people. It is one of the fastest growing areas in South Asia, and is subject to extreme pollution from local sources and transport from the Indo-Gangetic Plain. NAMaSTE-2 uses an aerosol mass spectrometer and positive matrix factorization (PMF) to establish aerosol composition and diurnal patterns at three sequential sites within a 15km radius during winter of 2018 .

The mean PM2.5 at these sites across the campaign is 65.2 µg m-3, exceeding the 24-hour WHO threshold of 25 µg m-3. Overnight PM2.5 concentrations increase up to 379.8 µg m-3 due to confinement from temperature inversions. Strong afternoon westerly winds are the main transport out of the valley , diluting PM2.5 concentrations to below 50 µg m-3.

The first site, Dhulikhel, along the valley rim, has minimal urban influence. Mean PM1 here is 47.9 µg m-3 ranging from 10.3 to 148.3 µg m-3. PM1 is composed of 54% Organic Aerosol (OA), 15% Black Carbon (BC), 5% Brown Carbon (BrC), 8% SO4, 10% NO3, 6% NH4, 2% Chl. PMF analysis on the OA factors this fraction into 57% oxygenated OA (OOA), 15% trash burning (TBOA), and 10% from local sulfate containing OA (LSOA), the remainder is biomass burning and hydrocarbon like OA (BBOA, HOA).

A 2nd site, Ratnapark, is at the busiest intersection in the city center. The mean PM1 is 102.2 µg m-3 ranging from 7.4 to 323.2 µg m-3. PM1 composition from AMS measurements are 45% OA, 1% BrC, 26% BC, 8% SO4, 7% NO3, 7% NH4, 7% Chl. OOA from PMF makes up a smaller fraction of the OA at Ratnapark, 34%, with 24% from HOA, and 18% from BBOA. TBOA makes up 14% of OA, and LSOA only 10%. The fraction of BBOA and HOA at this site is twice that of Dhulikhel.

The 3rd site, Lalitpur, a suburban site, has direct influence from industry. The mean PM1 at this site is 105.9 µg m-3 ranging from 14.2 to 369.4 µg m-3. PM1 is dominated by OA, similar to other sites, with composition proportionally 45% OA, 22% BC, 13% SO4, 9% NO3, 8% NH4, 4% Chl. OOA is 40% of OA at Lalitpur, with HOA 24%, and LSOA a further 17%. BBOA is 13% here, and TBOA only 6%. Primary emission of sulfates from coal combustion has a 60% greater impact at Lalitpur compared to other sites.

Differences in aerosol composition at each location suggests that multi-site measurements are essential to understand spatial variability and air quality in areas with sparse measurement infrastructure.

<< Previous Abstract | Next Abstract >>