Rain-Induced Soil NOx Emission From India During the Onset of the Summer Monsoon: A Satellite Perspective

Rain-induced soil NOx 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 NOx 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 NOx pulsing after the onset of summer monsoon rainfall over the dry soil in the study regions. Relating OMI tropospheric NO2 columns to surface NOx emission, soil emission accounts for an average emission flux of similar to 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.