SPATIAL AND TEMPORAL PATTERNS IN NITROGEN-DIOXIDE CONCENTRATIONS IN A HOT DESERT REGION

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 NO2 concentrations were analysed, and NO2 levels were only significantly correlated with temperature (r = 0.63). Only February, a winter month, showed a significantly lower concentration of NO2 with an overall mean value of 23 mugm-3, whereas in August, a summer month, it was 33 mugm-3. The results revealed that in a hot region like Bahrain, NO2 concentrations do not show significant monthly variations. Also summer-averaged NO2 values exceeded corresponding spring and winter values. In cold regions opposite patterns were observed. Moreover, the results revealed significant spatial variations in NO2 concentrations. In suburban areas with low traffic density, the overall mean NO2 level was 15, with a range of 12-17 mug m-3, while in urban areas with high traffic density, the overall mean value was 52 with a range of 44-60 mug m-3. The mean NO2 value in industrial sites with low traffic density was 21 with a range of 14-27 mug m-3, whereas in the same areas near major roads, it was 32 with a range of 31-32 mug m-3. These results indicate that automobiles exhaust are the dominant source of NO2 in Bahrain. The highest NO2 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 NO2 levels.