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. 2021 Nov 13:2021:4258816.
doi: 10.1155/2021/4258816. eCollection 2021.

Spatial Extent and Distribution of Ambient Airborne Particulate Matter (PM2.5) in Selected Land Use Sites in Nairobi, Kenya

Caroline Kiai  1 , Christopher Kanali  2 , Joseph Sang  1 , Michael Gatari  3
Affiliations

Spatial Extent and Distribution of Ambient Airborne Particulate Matter (PM2.5) in Selected Land Use Sites in Nairobi, Kenya

Caroline Kiai et al. J Environ Public Health. .

Abstract

Air pollution is one of the most important environmental and public health concerns worldwide. Urban air pollution has been increasing since the industrial revolution due to rapid industrialization, mushrooming of cities, and greater dependence on fossil fuels in urban centers. Particulate matter (PM) is considered to be one of the main aerosol pollutants that causes a significant adverse impact on human health. Low-cost air quality sensors have attracted attention recently to curb the lack of air quality data which is essential in assessing the health impacts of air pollutants and evaluating land use policies. This is mainly due to their lower cost in comparison to the conventional methods. The aim of this study was to assess the spatial extent and distribution of ambient airborne particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5) in Nairobi City County. Seven sites were selected for monitoring based on the land use type: high- and low-density residential, industrial, agricultural, commercial, road transport, and forest reserve areas. Calibrated low-cost sensors and cyclone samplers were used to monitor PM2.5 concentration levels and gravimetric measurements for elemental composition of PM2.5, respectively. The sensor percentage accuracy for calibration ranged from 81.47% to 98.60%. The highest 24-hour average concentration of PM2.5 was observed in Viwandani, an industrial area (111.87 μg/m³), and the lowest concentration at Karura (21.25 μg/m³), a forested area. The results showed a daily variation in PM2.5 concentration levels with the peaks occurring in the morning and the evening due to variation in anthropogenic activities and the depth of the atmospheric boundary layer. Therefore, the study suggests that residents in different selected land use sites are exposed to varying levels of PM2.5 pollution on a regular basis, hence increasing the potential of causing long-term health effects.

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Conflict of interest statement

The authors declare that they have no conflicts of interest regarding the publication of this paper.

Figures

Figure 1
Figure 1
Location of selected sampling sites and their respective zone [9] for PM2.5 mass concentration level monitoring in Nairobi City County, Kenya.
Figure 2
Figure 2
Sensor accuracies in percentage obtained in this study in comparison with accuracy percentages reported in a study that used a similar sensor model. Red dots represent accuracy values reported by Badura et al. [24].
Figure 3
Figure 3
24-hour mean distribution of PM2.5 mass concentration (μg/m³) in the selected land use sites in Nairobi City County.
Figure 4
Figure 4
Hourly distribution of PM2.5 mass concentration (μg/m³) in the selected land use sites in Nairobi City County.
Figure 5
Figure 5
Spatial distribution of mean hourly PM2.5 mass concentration in Nairobi City County.
Figure 6
Figure 6
The average 8-hour average PM2.5 concentration levels in the selected land use sites within Nairobi City County.
Figure 7
Figure 7
Comparison between the average sensor-based monitoring and gravimetric-based using cyclone pump samplers (BGI 400S) concentration.
Figure 8
Figure 8
The relative percentage concentrations of major elements in PM2.5 collected in the filter samples using Cyclone pump samplers (BGI 400S) for selected land use sites in Nairobi City County for an 8-hour period: (a) KCM, (b) KCL, (c) KCA, (d) KCI, (e) KCC, (f) KCK, (g) KCF, and (h) KCU.
See this image and copyright information in PMC

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