Assessment Of Ozone, Nitrogen Oxide, Air Particulate Matter (PM10) And Trace Elements Levels In The Ambient Air Of Nairobi City.

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 or most vehicles > plus the use of leaded gasoline. This study was carried out to determine the levels or nitric oxide (NO), nitrogen dioxide (N02), ozone. and air particulate matter (PM 10). in the ambient air of Nairobi city. Th~ ~O-N02-NO\ were measured hy Thermo Environmental Instruments Inc. (TEl) Model 14B Chcmiluminescence I NO-N02-NOx Analyzer, ozone by DASIBI Series 1003 UV Photometer and air particulate matter by the "Gent" Stacked Filter Unit (SFU). a dichotomous sampler. An automatic vehicle counter was used for determining the vehicle density at the sampling point. Gas measurements and analysis was done simultaneously at the sampling site, while the air particulate matter was by gravimetric and elemental composition by Energy Dispersive X-ray Fluorescence (EDXRF) technique. Sampling was done once every week for a period of three months (February to April 2000). Hourly average concentrations or N02• NO and 0, were measured s simultaneously from 9:00 a.m to 5:00 p.m .. at a roundabout connecting two main highways (University and Uhuru) in the city. The findings of the study show that the values obtained for Pb, Mn, Fe, Br, Zn, Cu and Ca are within the World Health Organization (WHO) guidelines. Lead concentrations ranged from 0.051 to 1.106 ug/nr': Fe, 0.149 to 3.154 ug/rn '; Mn, 0.002 to 0.526 ug/m': Cu. 0.041 (Lower limit of detection-Ll.D) to 0.150 ug/rn '; Br, 0.016 (LLD) to 0,430 ug/rrr': In. 0.025 ~LLD) to 0.140 ug/m ' and Ca, 2.180 to 5.389 ug/m'. Concentrations of N02. NO and 03 were also within the 8-hour World Health Organisation (WHO) limits with levels ranging from 0.011-0.976 ppm for NO, 0.001-0.263 ppm for N02 and LLD-0.126 ppm for ozone. The 03 levels were slightly higher in the afternoons when solar intensity was high especial1y the days with cloud cover or less than 3 Oktas. The mean level of PMIO was 239±126 ug/rn:' while the range was 66.66 _ 444.45 ug/m ' .. In the dry months of F ebruary and March. coarse particulates accounted for more than 70 % of PM)o. Analysis of the data shows strong correlation (1'=0.966) between fine (O.4~lm) particulates and NO. indicating the importance of traffic as a common source for both fine particulates and NO. However, coarse particulates, NOl and 0" showed poor correlation with motor vehicle density. There was also positive correlation between Pb and Br (r=0.930). while Fe, Ca and Mn were also positively correlated (r= 0.868. 0.0 I 0 and 0.326. respectively) with the coarse particulate matter. The high correlation between Ph and Br and motor vehicles suggests their main source being motor vehicle emissions. Ca, Fe and Mn are most probably from resuspended dust particles since they correlated well with the coarse particulate. The WHO as well as other studies show that the values obtained in this study. especially for fine particulate matter. . ."., lead and ozone could result in adverse health effects such as acute respiratory infection, asthma attacks. and low IQ and' hyperactivity in human. The health implications of these results are also discussed