Role of lightning in NOx production: direct atmospheric pathways and indirect contributions via forest fires in Nepal

Abstract

Nepal experiences rampant forest fires during the dry season (March-June) coinciding with the lightning peak season. Forest fires emit a large amount of gaseous pollutants that adversely impact the environment and hence our climate. Although unexplored, lightning strikes can be a potential cause of forest fires that in turn deleteriously impact on our environment. This study investigates the possible role of lightning strikes in generating nitrogen oxides (NOx) referred to as LNOx considering the forest fires across Nepal. We examined forest fires and lightning activities that occurred between 2015 and 2023. We utilized lightning data obtained from VAISALA’s GLD-360 and fire data obtained from NASA’s MODIS.  An examination of time lag between the peak lightning activities and the fire events unveiled that fire events lag 5 to 20 days with an average of 11.78 days. An exploration into the remote national parks revealed that lightning strikes with higher magnitude over 40 kA are more likely to ignite fire. The tropospheric NOx has significantly increased by an order of magnitude during the pre-monsoon season coinciding with the lightning and forest fire season as compared to that in the preceding winter season signifying that lightning produces enormous NOx in our atmosphere. This study lays a strong foundation for a robust study on the quantitative contribution of lightning in producing NOx.