Exploring the Spatial Variation Characteristics and Influencing Factors of PM2.5Pollution in Nairobi City, Kenya: A preliminary Analysis

Abstract

Background Quality of air is an important determinant of health hence of public health importance for a city. If exposure to air pollution varies spatially, this may lead to significant inequality in related health risk. Since air pollution combines with other aspects of the social and physical environment, a likely scenario would be a disproportional disease burden in less affluent parts of society. Previous studies using portable filter-based air samplers carried in backpacks by technicians over two weeks showed that mean daytime concentrations of particulate matter (PM2.5) in Nairobi ranged from 10.7 at the rural background site to 98.1 μg/m3 on a sidewalk in the central business district.Aim Our study aimed at establishing long term exposure of PM2.5 pollution and factors influencing concentrations.Methods We examined PM2.5 pollution in eight Planning Zones in Nairobi between September 2019 and February 2020 using Nephelometers (E-Samplers) calibrated against the Gold Standard reference method, the Beta Attenuation Monitor (BAM) 1022.Results PM2.5 pollution was found to vary in different parts of the city being highest 38.01 ug/m3 around the central business district, and lowest 12.72 ug/m3 in the southern suburbs of the city. We demonstrate that an order of magnitude rises in the relative humidity (RH) led to a decrease in the level of PM2.5 concentration by a factor of 0.14 ug/m3. An increase in temperature by 10C conversely led to an additional rise of PM2.5 concentrations by a factor of 0.49 ug/m3.Conclusions These preliminary findings suggest that meteorological factors had some effects on the diffusion mechanism of PM2.5 pollution in Nairobi. However, we are analyzing possible contribution of natural environmental conditions and socio-economic factors for a more comprehensive explanation of spatial exposure to PM2.5 pollutants among Nairobi residents.