Lightning-produced NOx budget over the Highveld region of South Africa

Measurements of lightning events recorded by a lightning position and tracking system (LPATS) were used to estimate the contribution of lightning to the nitrogen oxide (NOx) burden over the Highveld region (taken as the 4° area, Lat. 25–29°, Lon. 27–31°) of South Africa. Lightning data collected in the year 2002, comprising a total of 2 417 074 cloud-to-ground (CG) strokes, were analyzed. Lightning strokes were grouped into flashes by considering strokes occurring within radii of 10 km and time intervals of 1 s apart as belonging to the same lightning flash. Making use of a production rate of 10×1016 molecules of NO J−1 and an energy dissipation of 6.7×109 J flash−1, an emission factor of 51.2 kg NO2 flash−1 was derived. This emission factor was employed to calculate the lightning-produced NOx (LNOx) budget of 65 (2.8–200) kt NO2 yr−1 over the Highveld region. Our calculated LNOx is about 9% of reported NOx emissions from coal-fired power plants over the Highveld during 2002. An annual contour plot of LNOx showed that the distribution of NOx production over the Highveld is highly non-uniform, with high concentrations of LNOx over the central Highveld. These results indicate that in evaluating NOx and tropospheric ozone chemistry over the South African Highveld both natural lightning and industrial sources of NOx need to be taken into account.