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 NO_X) and sulphur dioxide (SO₂) in Nairobi city by use of passive sampling method. In this technique, Triethanolamine (TEA) and potassium tetrachloromercurate (TCM) solutions were used as trapping agents and air samples which were sampled from twelve sites within Nairobi city were analyzed spectrophotometrically. The detection limit of passive sampling method was found to be 7µg/m³ and 4 µg/m³ and precision was 4 µg/m³ and 3 µg/m³ for NO₂ and SO₂, respectively for a 24-hour sampling. The highest 24-hour mean concentrations of NO_X 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/m³ and 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 NO_X and SO₂ recorded during the dry season were higher than those of the wet season. The trend of levels of NO_X and SO₂ followed the vehicular density and areas with high vehicular traffic and industrial activities had high levels of NO_X and SO₂.