Submicron Aerosol Composition and Source Contribution across the Kathmandu Valley, Nepal, in Winter

The Kathmandu valley experiences an average wintertime PM1 concentration of ∼100 μg m–3 and daily peaks over 200 μg m–3. We present ambient nonrefractory PM1 chemical composition, and concentration measured by a mini aerosol mass spectrometer (mAMS) sequentially at Dhulikhel (on the valley exterior), then urban Ratnapark, and finally suburban Lalitpur in winter 2018. At all sites, organic aerosol (OA) was the largest contributor to combined PM1 (C-PM1) (49%) and black carbon (BC) was the second largest contributor (21%). The average background C-PM1 at Dhulikhel was 48 μg m–3; the urban enhancement was 120% (58 μg m–3). BC had an average of 6.1 μg m–3 at Dhulikhel, an urban enhancement of 17.4 μg m–3. Sulfate (SO4) was 3.6 μg m–3 at Dhulikhel, then 7.5 μg m–3 at Ratnapark, and 12.0 μg m–3 at Lalitpur in the brick kiln region. Chloride (Chl) increased by 330 and 250% from Dhulikhel to Ratnapark and Lalitpur on average. Positive matrix factorization (PMF) identified seven OA sources, four primary OA sources, hydrocarbon-like (HOA), biomass burning (BBOA), trash burning (TBOA), a sulfate-containing local OA source (sLOA), and three secondary oxygenated organic aerosols (OOA). OOA was the largest fraction of OA, over 50% outside the valley and 36% within. HOA (traffic) was the most prominent primary source, contributing 21% of all OA and 44% of BC. Brick kilns were the second largest contributor to C-PM1, 12% of OA, 33% of BC, and a primary emitter of aerosol sulfate. These results, though successive, indicate the importance of multisite measurements to understand ambient particulate matter concentration heterogeneity across urban regions

Wintertime Air Quality across the Kathmandu Valley, Nepal: Concentration, Composition, and Sources of Fine and Coarse Particulate Matter

The Kathmandu Valley in Nepal experiences poor air quality, especially in the dry winter season. In this study, we investigated the concentration, chemical composition, and sources of fine and coarse particulate matter (PM2.5, PM10, and PM10–2.5) at three sites within or near the Kathmandu Valley during the winter of 2018 as part of the second Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE 2). Daily PM2.5 concentrations were very high throughout the study period, ranging 72–149 μg m–3 at the urban Ratnapark site in Kathmandu, 88–161 μg m–3 at the suburban Lalitpur site, and 40–74 μg m–3 at rural Dhulikhel on the eastern rim of the Kathmandu Valley. Meanwhile, PM10 ranged 194–309, 174–377, and 64–131 μg m–3, respectively. At the Ratnapark site, crustal materials from resuspended soil contributed an average of 11% of PM2.5 and 34% of PM10. PM2.5 was largely comprised of organic carbon (OC, 28–30% by mass) and elemental carbon (EC, 10–14% by mass). As determined by chemical mass balance source apportionment modeling, major PM2.5 OC sources were garbage burning (15–21%), biomass burning (10–17%), and fossil fuel (14–26%). Secondary organic aerosol (SOA) contributions from aromatic volatile organic compounds (13–23% OC) were larger than those from isoprene (0.3–0.5%), monoterpenes (0.9–1.4%), and sesquiterpenes (3.6–4.4%). Nitro-monoaromatic compoundsof interest due to their light-absorbing properties and toxicityindicate the presence of biomass burning-derived SOA. Knowledge of primary and secondary PM sources can facilitate air quality management in this region