Rain-induced soil NO_x emission from India during the onset of the summer monsoon: a satellite perspective

Abstract

Rain-induced soil NO_x emission in the rural regions in India has been investigated using satellite observations of daily tropospheric NO₂ columns from the Ozone Monitoring Instrument (OMI). We selected three rural regions with low population density where industrial and transportation activities are notably less in comparison to other regions of India. We show that OMI-derived tropospheric NO₂ columns capture the NO_x pulses from soil during the onset of the rainy season (June) over the regions considered in our analysis. Strong enhancements in tropospheric NO₂ columns after the active spell of precipitation and subsequent decrease during the break spell have been observed. We argue that this enhancement is due to rain-induced soil NO_x pulsing after the onset of summer monsoon rainfall over the dry soil in the study regions. Relating OMI tropospheric NO₂ columns to surface NO_x emission, soil emission accounts for an average emission flux of -23-28 ng N m⁻¹ s⁻¹ during the pulsing event. Lightning is unlikely to account for the enhanced OMI tropospheric NO₂ columns over the study regions.