| dc.description.abstract | Motor vehicle emissions are a major source of air pollution in most urban centers. In Kenya, Nairobi city has the highest traffic density and is therefore a particular cause for concern due to the poor maintenance standards of most vehicles plus the use of leaded gasoline. This study was carried out to determine the levels of nitrogen oxides (nox), suspended particulate matter (PM10), ozone (O3) and heavy metals in the SPM collected from the ambient air of Nairobi city. Sampling was done once every week for a period of three months (February to April 2000). Hourly average concentrations of N02, NO and O3 were measured simultaneously from 9.00 am to 5.00 p.m., at a roundabout connecting two main highways (University and Uhuru) in the city. PM10 was collected using Gent Stacked Filter Unit (SFU) air sampler on nuclepore filters (0.4 and 8.0 ?m pore size for fine and coarse filters respectively) which were weighed and analysed for trace elements by Energy Dispersive X-ray Fluorescent (EDXRF) technique. Nitrogen oxides were analysed with thermo electron's Chemiluminescent nox Model 14B analyser while ozone was by using DASIBI ozone monitor, Model 1003 AH. An automatic vehicle counter was used For determining the vehicle density at the sampling point. The findings of the study show that the values obtained for Pb, Mn, Fe, Br, Zn, Cu and Ca are within the Who guidelines. Lead concentrations ranged from 0.051 to 1.106?g/m3; Fe, 0.149 to 3.154?g/m3; Mn, 0.002 to 0.; Fe, 0.149 to 3.154?g/m3; Mn, 0.002 to 0.526?g/m3; Cu, lower limit of detection (LLD) to 0.15?g/m3; Br, LLD to 0.43?g/m3; Zn, LLD to 0.14 ?g/m3 and Ca 2.18 to 5.389?g/m3. Concentrations of NO2, NO and O3 were also within the 8-hour Who limits with levels ranging from 0.011-0.976 ppm for NO, 0.001-0.2628 ppm for NO2 and LLD-0.1258 ppm for ozone. The O3 levels were slightly higher in the afternoons when solar intensity was high especially the days with cloud cover of less than 3 Oktas. PM10 levels were, however, above the Who guidelines for most of the days. The mean (PM10) was 239 ?g/m3 while the range was 66.657 - 444.45?g/m3. In the dry months of February and March, coarse particulates account for more than 70 % of PM10. Analysis of the data shows strong correlation (r=0.966) between fine (0.4?m) particulates and NO, indicating the importance of traffic as a common source for both fine particulates and NO. Coarse particulates, NO2 and O3, however shows poor correlation with motor vehicle density. There is also positive correlation between Pb and Br (r=0.930), while Fe, Ca and Mn are positively correlated with coarse particulate matter. The high correlation between Pb and Br and motor vehicles suggests their main source as motor vehicle emission. Ca, Fe and Mn are most probably from resuspended dust particles since they correlate well with coarse particles. The health implications of these results are also discussed | en_US |
