Cement and brick factories contribute elevated levels of NO2 pollution in Nepal: Evidence of high-resolution view from space

Abstract

An upsurge in the pollution level in areas with a high concentration of brick and cement factories in Nepal is concerning. Nitrogen dioxide (NO₂), a key air quality indicator, can be effectively monitored from space. This study utilizes high-resolution satellite observations of NO₂ from the TROPOspheric Monitoring Instrument (TROPOMI). It examines the NO₂ distribution over areas with emerging sources of nitrogen oxides from brick and cement factories from 2018 to 2021. Rapid growth of brick and cement factories has turned the Lumbini-Butwal-Palpa corridor, in Midwest Nepal, more polluted than the capital city Kathmandu. Between 2019 and 2021, NO₂ levels in this corridor rose considerably, while it remained steady in the Kathmandu Valley. TROPOMI-derived NO₂ levels and inferred NO_x emissions over the corridor nearly doubled in the span of three years. Conversely, Kathmandu Valley exhibited no significant changes except in 2020 when NO₂ and NO_x levels declined. This drop coincided with COVID-19-related travel restrictions and other reduced activities. NO₂ pollution recorded by the Ozone Monitoring Instrument (OMI) from 2005 to 2019 shows an annual NO₂ increase of ∼3.5 % over both regions. A comparison between NO_x emissions from the 2018 EDGAR inventory and TROPOMI-derived estimates for 2019 reveal comparable values over the Lumbini-Butwal-Palpa corridor but around 35 % higher estimates over Kathmandu. This discrepancy over the capital city, as well as the rapid rise in emissions over the Lumbini-Butwal-Palpa corridor due to a large-scale development of cement and brick industries, highlights the need for timely updates in bottom-up emission inventory.