DETERMINATION OF NOX AND SO2 CONCENTRATION LEVELS IN NAIROBI CITY, KENYA, BY USE OF PASSIVE SAMPLERS

Abstract

This research work describes the determination of the levels of nitrogen monoxide, nitrogen dioxide (termed as NOX) and sulphur dioxide (SO2) in Nairobi city by use of passive sampling method. In this technique, Triethanolamine (TEA) solution and potassium tetrachloromercurate (TCM) solution were used as trapping agents and air samples which were sampled from twelve sites within Nairobi city were analyzed spectrophotometrically. The results obtained by passive sampling method were statistically comparable to those of active sampling method used as reference method. There was a good agreement with coefficient of correlations of 0.9819 NO, 0.9966 NO2 and 0.9968 SO2. The highest 24-hour mean concentrations of NOX and SO2 were recorded at City Kabanas site along Nairobi-Mombasa road with 300.61 ± 8.21 μg/m3 and 181.35± 2.46 μg/m3, respectively and the lowest mean concentrations of NOX and SO2 were recorded at Githurai site with 169.92 ± 6.12 μg/m3and 85.60 ± 0.78 μg/m3, respectively. The overall mean levels for these air pollutants were; 82.87 ± 6.13 μg/m3 for NO, 136.78 ± 9.72 μg/m3 for NO2 and 127.66 ± 10.45 μg/m3 for SO2. The recorded level of NO2 in Nairobi troposphere was found to be above the WHO value of 100μg/m3, that of SO2 was within the WHO value of 125μg/m3 and that of NO was below the WHO value of 400μg/m3. Furthermore, it was found that levels of NOX and SO2 recorded during the dry season were higher than those of the wet season. The trend of levels of NOX and SO2 followed the vehicular density and areas with high vehicular traffic and industrial activities had high levels of NOX and SO2. Finally, it was demonstrated that activated charcoal is a good absorbent for NO, NO2 and SO2 from the atmosphere.