Mobile Aerosol Mass Spectrometry Measurements in the Kathmandu Valley. The Impact of Local Sources and Meteorology to Spatial Variability of Aerosol Composition

Air pollution in the Kathmandu valley is influenced by a variety of domestic and industrial sources such as garbage and biomass burning, brick kilns, and vehicular emissions. During non-monsoon seasons, the air quality index is considered hazardous, and consequently, air pollution is a leading cause of death in Nepal. During winter and spring of 2017-18, part two of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE-2) involved stationary sampling of gas and aerosol phase species in four locations across Nepal as well as 14 mobile measurement drives throughout the Kathmandu valley, Nepal. This work presents spatially and temporally resolved aerosol mass spectrometry and gas phase measurements from a mobile laboratory capable of high time resolution aerosol composition measurements. Spatially resolved aerosol composition results highlight chemical differences in aerosol due to strong regional sources, topography, and meteorology. For example, aerosol composition in regions with a high concentration of brick kilns had enhanced concentrations of sulfate aerosol, consistent with emission factors measured from brick kilns. Similarly, small towns outside of Kathmandu exhibited strongly elevated concentrations of chloride and organic aerosol due to garbage burning. These results are important for apportionment of the aerosol burden in the valley to their sources, and the consequent reduction of aerosol emissions.