An assessment of spatial and temporal variations of nitrogen dioxide over Mpumalanga highveld

Abstract

High concentrations of nitrogen containing compounds are a growing concern in the Mpumalanga Highveld with satellite measurements confirming high NO2 in different hotspots around the globe including Mpumalanga Highveld. Nitrogen oxides are produced from the eight coal fired power stations in Mpumalanga Highveld, a petrochemical industry in Secunda, steel processing plants in Middelburg and Emalahleni and tail emissions from traffic in the Mpumalanga Highveld. Monitoring of these trace gases is important to estimate an impact that they cause to human health and the environment and also to implement air quality emission standards by government Authorities. A 2008 data from Elandsfontein monitoring station and seven other monitoring stations in the Mpumalanga Highveld have been compared with the 2008 satellite data taken from Ozone Monitoring Instrument (OMI) overpass over the Mpumalanga Highveld. Elandsfontein monitoring station is situated on the highly industrialized Mpumalanga Highveld and its purpose is to monitor impacts of stack emissions on air quality. The study focuses on a 2008 nitrogen dioxide dataset which was taken from Elandsfontein monitoring station. An analysis of data from other monitoring stations located in Ermelo, Bulfour, Hendrina, two stations in Middelburg, Emalahleni, Standerton and Secunda have been undertaken to indicate temporal variation and spatial distribution of nitrogen dioxide in the Mpumalanga Highveld. Temporal variability and spatial distribution of nitrogen dioxide in the Mpumalanga Highveld were estimated by analyzing the ground based measurements and satellite data sets. Smoke stacks emit NO into the atmosphere where it reacts with atmospheric oxygen to form NO2. Subsequent reactions of NO2 result in the formation of ozone. The satellite derived data has been modelled and compared with the ground measured data. Meteorological factors including diurnal and temporal variations of the NO2 concentrations have been analyzed to establish differences and similarities between the two data sets. Vertical column densities of nitrogen oxides from satellite measurements with high resolution are presented in mole x (1015)/cm2 and together with ground measured data from other eight air quality monitoring stations have been converted into μg/m3. Analysis of both data sets have been done on the same units, μg/m3 . Seasonal and diurnal variations between the two data sets seem to form the same graphical trends by showing high concentrations during winter than in summer. Ground measured and satellite born datasets do not agree because clouds, air mass factor, aerosols and surface albedo create retrieval errors on the satellite data.