Nitrogenous and carbonaceous aerosols in PM_(2.5) and TSP during pre-monsoon:Characteristics and sources in the highly polluted mountain valley

摘要

This study reports for the first time a comprehensive analysis of nitrogenous and carbona-ceous aerosols in simultaneously collected PM_(2.5) and TSP during pre-monsoon(March-May 2018)from a highly polluted urban Kathmandu Valley(KV)of the Himalayan foothills.The mean mass concentration of PM_(2.5)(129.8 μg/m^(3))was only-25%of TSP mass(558.7 μg/m^(3))indicating the dominance of coarser mode aerosols.However,the mean concentration as well as fractional contributions of water-soluble total nitrogen(WSTN)and carbonaceous species reveal their predominance in find-mode aerosols.The mean mass concentration of WSTN was 17.43±4.70 μg/m^(3)(14%)in PM_(2.5) and 24.64±8.07 μg/m^(3)(5%)in TSP.Moreover,the fractional contribution of total carbonaceous aerosols(TCA)is much higher in PM_(2.5)(~34%)than that in TSP(~20%).The relatively low OC/EC ratio in PM_(2.5)(3.03±1.47)and TSP(4.64±1.73)suggests fossil fuel combustion as the major sources of carbonaceous aerosols with contributions from secondary organic aerosols.Five-day air mass back trajectories sim-ulated with the HYSPLIT model,together with MODIS fire counts indicate the influence of local emissions as well as transported pollutants from the Indo-Gangetic Plain region to the south of the Himalayan foothills.Principal component analysis(PCA)also suggests a mixed contribution from other local anthropogenic,biomass burning,and crustal sources.Our re-sults highlight that it is necessary to control local emissions as well as regional transport while designing mitigation measures to reduce the KV's air pollution.