Study on the characteristic emission loading from the public transport and its contribution for air quality degradation over the Kathmandu valley : Grided emission estimation and dispersion modeling

Abstract

The Kathmandu valley is witnessing an extremely poor air quality from years. The degradation of air quality over Kathmandu is often found to be associated with the spontaneous urbanization, haphazard industrial expansions and vehicular fleet. Present study was conceived to understand the contribution of transport sector in degrading the air quality of Kathmandu valley. We developed a comprehensive gridded emission inventories of potential pollutants and performed particulate pollutant dispersion modelling using a comprehensive Chemical Transport Modelling (CTM) at the horizontal grid resolution of 1 km 2 over an area of 70 km x 70 km that covers the Kathmandu valley and its immediate surroundings, initialized with the Weather Research and Forecasting (WRF) simulated meteorological fields. The gridded emission inventory showed about 1918.17 kg km −2 of TSP, 12872.74 kg km −2 of CO, 6925.82 kg km −2 of NOx and 708.41 kg km −2 of SO2 are currently loaded into the atmosphere of the valley per day from the public transport over the Kathmandu valley. CTM simulation shows the ambient concentration of PM2.5 due to public transport fleets appears a minimum during the day time and remains maximum during the night and morning times. The pollutants released over the valley are transported to the east and are flushed out into the eastern neighbouring valley. The contribution of the public transport fleet to the deterioration of ambient air quality of the valley appears significant compared to total emission from transport sector.