Seasonal variation of ozone and black carbon observed at Paknajol, an urban site in the Kathmandu Valley, Nepal

A first-of-its-kind year-long study (2013–2014) at Paknajol, Kathmandu, reveals persistent severe air pollution driven by local sources and regional open vegetation fires. The research found that ozone (O₃) and black carbon (BC) concentrations, particularly during pre-monsoon afternoons/evenings, are strongly influenced by photochemistry, planetary boundary layer dynamics, and westerly atmospheric circulations. High O₃ levels correlate with mixing processes between residual layers and the PBL, while BC spikes reflect local emissions. The study highlights dangerous air quality conditions for over 3 million residents, threatening health and ecosystems. These findings provide critical data to design mitigation strategies for acute pollution events in the Kathmandu Valley.

Putero, D., Cristofanelli, P., Marinoni, A., Adhikary, B., Duchi, R., Shrestha, S. D., Verza, G. P., Landi, T. C., Calzolari, F., Busetto, M., Agrillo, G., Biancofiore, F., Di Carlo, P., Panday, A. K., Rupakheti, M., & Bonasoni, P. (2015). Seasonal variation of ozone and black carbon observed at Paknajol, an urban site in the Kathmandu Valley, Nepal. Atmospheric Chemistry and Physics, 15(24), 13957–13971. https://doi.org/10.5194/acp-15-13957-2015