Lightning-produced NO_x 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 (NO_x) 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 NO_x (LNO_x) budget of 65 (2.8-200) kt NO₂ yr^-1 over the Highveld region. Our calculated LNO_x is about 9% of reported NO_x emissions from coal-fired power plants over the Highveld during 2002. An annual contour plot of LNO_x showed that the distribution of NO_x production over the Highveld is highly non-uniform, with high concentrations of LNO_x over the central Highveld. These results indicate that in evaluating NO_x and tropospheric ozone chemistry over the South African Highveld both natural lightning and industrial sources of NO_x need to be taken into account.