Studies on the levels of sulphur dioxide, nitrogen dioxide, ammonia, and hydrogen chloride in ambient air of Harare, Zimbabwe

Abstract

The concentrations of sulphur dioxide, nitrogen dioxide, ammonia, and hydrogen chloride, in the ambient atmosphere of Harare were monitored over a period of one year (1988) at four selected sites — university campus, city centre, industrial area, and Msasa, an industrial site in the vicinity of a fertilizer factory. The diurnal variations varied from day to day and sulpur dioxide and nitrogen dioxide levels rose with sunlight hours, reaching peak values about midday which were sustained on some days through till late afternoon. Normally, a decreasing trend is observed by the evening. The profile of the seasonal variation in the average dayly concentrations of all the pollutants are shown for the industrial are sampling point. Sulphur dioxide levels were observed, sustained at high levels (90–120 μg m −3) during winter extending into spring and lower levels during the rainy season. Hydrogen chloride in the winter and spring was maintained at about 40 μg m −3. Of the four sites, the university area was found to be relatively clean with minimum and maximum daily average levels (in μg m −3) recorded during the year, being SO 2 (2.0–52.6), NO 2 (2.0–17.2), NH 3 (1.9–8.1), and HCl (9.0–55.1). The order of increasing pollutant concentrations was the city centre, the industrial area, and the Msasa area. In the Msasa area, the pollution originated from the point source, the fertilizer factory. The minimum and maximum diurnal arthamatic means (in μg m −3), over the year observed, were SO 2 (14.0–242.0), NO 2 (4.5–27.4), NH 3 (2.0–45.3), and HCl (14.8–77.0). The correlation plot of NH 3/SO 2 versus SO 2 gave a slope of 7.7 × 10 −3 (corr. 0.69), indicating that high sulphur dioxide levels facilitate the removal of ammonia, possibly through aerosol formation from the ambient air.