Spatial and temporal patterns in nitrogen dioxide concentrations in a hot desert region

Abstract

This paper reports seasonal and spatial variations in the ambient air concentration of nitrogen dioxide throughout the State of Bahrain, from February to December 1992. Monitoring sites were chosen to include urban areas with high traffic density, suburban areas with low traffic density, commercial and industrial areas. Correlations between meteorological parameters and mean NO 2 concentrations were analysed, and NO 2 levels were only significantly correlated with temperature ( r = 0.63). Only February, a winter month, showed a significantly lower concentration of NO 2 with an overall mean value of 23 μgm −3, whereas in August, a summer month, it was 33 μgm −3. The results revealed that in a hot region like Bahrain, NO 2 concentrations do not show significant monthly variations. Also summer-averaged NO 2 values exceeded corresponding spring and winter values. In cold regions opposite patterns were observed. Moreover, the results revealed significant spatial variations in NO 2 concentrations. In suburban areas with low traffic density, the overall mean NO 2 level was 15, with a range of 12–17 μg m −3, while in urban areas with high traffic density, the overall mean value was 52 with a range of 44–60 μg m −3. The mean NO 2 value in industrial sites with low traffic density was 21 with a range of 14–27 μg m −3, whereas in the same areas near major roads, it was 32 with a range of 31–32 μg m −3. These results indicate that automobiles exhaust are the dominant source of NO 2 in Bahrain. The highest NO 2 levels were found in roads with high traffic density, which are narrow, with several traffic lights and roundabouts, suggesting the effect of road geometry on NO 2 levels.