Nitrogen oxide hot spots

Nitrogen oxide emissions for the South African Highveld region. The grey outline indicates the densely populated Gauteng province, containing the cities of Johannesburg and Pretoria. Blue circles indicate the location of coal-fired power stations, important hot spots of nitrogen oxide emissions. The upper panel shows the emission strength of the model-based emission inventory, based on 2008 data. The lower panel shows the emission estimates from the spaceborne OMI instrument for 2009–10. The use of satellite data improves the identification of the emission hot spots.