Rising pollution levels in Nepal's Kathmandu valley are a cause for concern. In a recent survey, tourists singled out air pollution as the most disturbing factor during their stay in the country. Specifically during the period between November and January, air pollution levels zoom in the region. During these winter months, the prevalent foggy conditions trigger a thermal inversion process, sealing pollutants within the valley.

Other reasons for the increasing pollution include haphazard urbanisation, unchecked growth of vehicular transport and concentration of industries in the bowl-shaped Kathmandu valley, which prevents easy escape of pollutants. Lack of stringent laws and ineffective implementation of existing ones compound the problem.

A recent survey by an environmental organisation indicates that air pollution levels have reached much higher concentrations than deemed acceptable by the World Health Organization (WHO).