Ambient air quality in the Kathmandu Valley, Nepal during the pre-monsoon: Concentrations and sources of particulate matter and trace gases (original) (raw)

Atmospheric Chemistry and Physics Discussions

The Kathmandu Valley in Nepal is a bowl-shaped urban basin that experiences severe air pollution that poses health risks to its 3.5 million inhabitants. As part of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE), ambient air quality in the Kathmandu Valley was investigated from 11 to 24 April 2015, during the pre-monsoon season. Ambient concentrations of fine and coarse particulate matter (PM 2.5 and PM 10 , respectively), online PM 1 , inorganic trace gases (NH 3 , HNO 3 , SO 2 , and HCl), and carbon-containing gases (CO 2 , CO, CH 4 , and 85 non-methane volatile organic compounds; NMVOC) were quantified at a semi-urban location near the center of the valley. Concentrations and ratios of NMVOC indicated that origins primarily from poorly-maintained vehicle emissions, biomass burning, and solvent/gasoline evaporation. During those two weeks, daily average PM 2.5 concentrations ranged from 30 to 207 µg m-3 , which exceeded the World Health Organization 24 hour guideline by factors of 1.2 to 8.3. On average, the non-water mass of PM 2.5 was composed of organic matter (48%), elemental carbon (13%), sulfate (16%), nitrate (4%), ammonium (9%), chloride (2%), calcium (1%), magnesium (0.05%), and potassium (1%). Large diurnal variability in