Temporal and Spatial Variations of the Levels of Ambient Particulate Matter (Pm2.5 & Pm10) in Nairobi City, Kenya

Abstract

Air pollution has become a major concern globally as it poses great threats to public health and welfare. In Kenya, studies show that there is increasing threat from poor air quality stemming from rapid urbanization. The factors that contribute to air pollution include transportation, stationary source fuel combustion, industrial processes and solid waste disposal, among others. Particulate matter (PM2.5 and PM10) is a major pollutant in cities such Nairobi city. Industrial and vehicular emission are the main sources of particulate matter. This study was conducted in Nairobi city to determine spatial, temporal variation and the particulate matter composition.in the ambient air. Temporal variability was achieved by assessing particulate matter from different location at eight hours’ intervals of time (three times) within 24 hrs and different months of the year with different seasons. On the other hand, spatial variability was determined by sampling different locations; residential, controlled and industrial as classified in EMCA Air Quality Regulation 2014. A portable mini-vol was used in sample collection of particulate matter in ambient air. The samples collected were analysed to determine the concentration of heavy metals (i.e., manganese, mercury, lead, arsenic, zinc, cadmium and chromium. The results show that the particulate matter in residential and controlled areas were high during the day. The mean and range values for PM10 concentrations in residentials areas were 40.61±18.55 µg/m3 and 23-86 µg/m3, respectively, while those for PM2.5 were 22.5±7.88 µg/m3 and 11-41 µg/m3, respectively. The mean and range values for the PM10 concentration in controlled zones were 31.92±23.28 µg/m3 and 11-45 µg/m3, respectively, while the PM2.5 a ranged between 7.36 to 31 µg/m3 with a mean value of 19.49±12.59 µg/m3. The observed range was 11-109 µg/m3 with average values of 38.77±31.14 µg/m3 for PM10 concentration and 8.36-72 µg/m3 with a mean of 23.5±16.27 µg/m3 for PM2.5 in the industrial zones. The lead concentration for residential, controlled and industrial area had a mean of 0.066±0.064, 0.336±0.354 and 1.102±0.592 µg/m3, respectively. These results are useful to planners of urban settlements such as Nairobi City as they provide real and visual perspective of spatial distribution of PM10 and PM2.5 particulate matter for enhanced safe public health and welfare decision making and planning.