Lightning NOx and Impacts on Air Quality

Lightning generates relatively large but uncertain quantities of nitrogen oxides (NOx), critical precursors for ozone and hydroxyl radical (OH), the primary tropospheric oxidants. Lightning NOx strongly influences background ozone and OH due to high ozone production efficiencies in the free troposphere, effecting small but non-negligible contributions to surface pollutant concentrations. Lightning globally contributes 3-4 ppbv of simulated annual-mean policy-relevant background (PRB) surface ozone, comprised of local, regional, and hemispheric components, and up to 18 ppbv during individual events. Feedbacks via methane may counter some of these effects on decadal time scales. Lightning contributes similar to 1 % to annual-mean surface particulate matter, as a direct precursor and by promoting faster oxidation of other precursors. Lightning also ignites wildfires and contributes to nitrogen deposition. Urban pollution influences lightning itself, with implications for regional lightning-NOx production and feedbacks on downwind surface pollution. How lightning emissions will change in a warming world remains uncertain.