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The Kathmandu Valley, which is surrounded by high hills and mountains, has been plagued by air pollution, especially in winter. We measured the levels of volatile organic compounds, nitrogen dioxide, nitrogen oxides, sulfur dioxide, ammonia, ozone, PM2.5, and carbon monoxide in the Kathmandu Valley during the winter to investigate the impact of vehicular emissions and the contribution of gaseous air pollutants to secondary pollutants. The most common gaseous pollutants were discovered to be gasoline components, which were emitted more frequently by engine combustion than gasoline evaporation. Considering the ethylene to acetylene ratio, it was discovered that most vehicles lacked a well-maintained catalyst. Compared to previous studies, it was considered that an increase in the number of gasoline vehicles offset the effect of the measures and exceeded it, increasing the level of air pollutants. Aromatics and alkenes accounted for 66–79% and 43–59% of total ozone formation potential in Koteshwor and Sanepa, respectively. In terms of individual components, it was determined that ethylene, propylene, toluene, and m-xylene all significantly contributed to photochemical ozone production. As those components correlated well with isopentane, which is abundant in gasoline vehicle exhaust, it was determined that gasoline vehicles are the primary source of those components. It was indicated that strategies for regulating gasoline vehicle exhaust emissions are critical for controlling the photochemical smog in the Kathmandu Valley.

Investigation of Air Pollutants Related to the Vehicular Exhaust Emissions in the Kathmandu Valley, Nepal