Effects of lightning on reactive nitrogen and nitrogen reservoir species in the troposphere

The impact of lightning on tropospheric reactive nitrogen NO x (NO + NO 2 ) and nitrogen reservoir species (HNO 3 , peroxyacetyl nitrate (PAN), N 2 O 5 , and HNO 4 ) has been evaluated using a global chemical/transport model. Comparison of calculations made with and without lightning show that lightning has a significant effect on the nitrogen species on a global scale, resulting in significant enhancements of NO x , HNO 3 , and PAN over the no lightning case. Of the nitrogen species, HNO 3 is influenced the most, comprising approximately 60 to 80% of the total increase in the nitrogen species concentration. The increase in PAN accounts for approximately 20 to 30% of the nitrogen enhancement by lightning in the middle troposphere. In the lower troposphere of the tropics, NO x is rapidly converted into HNO 3 due to the high OH concentration in this region. As a result, the enhancement in NO x from direct lightning emission is limited primarily to the upper troposphere. The conversion between NO x and less reactive nitrogen species (PAN and HNO 3 ) also plays an important role in affecting NO x , especially over the oceans where lightning activity is low. The model results suggest that recycling of NO x from the lightning‐enhanced PAN and HNO 3 produces 2 to 10 parts per trillion by volume (pptv) increases in NO x over the oceans in the lower troposphere of the tropics. The enhancement of NO x over the oceans can partially explain the observations of NO x (mixing ratios of typically 10–50 pptv) over the tropical oceans, which are characterized by higher concentrations than would be expected from direct transport of NO x from the continents.