Aerosol Dispersion Over a High Altitude Region: a Case Study of Kathmandu, Nepal

摘要

Air quality of the Kathmandu Valley has been degraded since few decades with the increase of urbanization in the Valley. The main objective of this study is to find the types of air pollutions and the pollution dispersion pattern in the Valley. A study involving numerical simulation of air dispersion was carried out for Kathmandu Valley and its vicinity using A2C flow/A2C t&d for the mid of April. PM10 and PM2.5 were sampled on quartz filter using the Omni frm sampler, and chemical components were analyzed in the laboratory. Black carbon (BC) was also monitored using the Aethalometer, and natural scenic vista were captured using digital camera (IMI:TECH:IMC-FF:1700018). Aerosol comprised ionic {Na+ (19%), Cl- (17%), Ca++ (14%), SO4-- (14%) and NH4+ (12%)} as well as non-ionic {Si, Fe, Cr, V, and Ni} components. Silicon (Si) comprised 60% of total non-ionic components and approximately 25% of the PM10. BC concentration occupied approximately 17% of the total aerosol; this showed that the BC emission in the Valley was alarming. Airborne dust, traffic emissions, fuels burning, and biomass burning were the primary emission sources. Diurnal variation of Mountain/Valley breeze was frequently experienced in the Valley. The Valley breeze was generated from 9 a.m. to 9 p.m. It transports and disperses air pollutants from the downtown of the Valley to the surrounding mountains. The pollutants generated mostly in the northern and central parts of the Valley dispersed throughout the Valley; however, comparatively smaller portion of the pollutants generated from the south and south-east region of the Valley dispersed downtown. In addition, a large portion of the pollutants were transported out of the Valley, into surrounding mountainous area, through the wind corridor.