The spatial–temporal variations of fine particulate matter (PM_2.5) in Akure, a city in southwestern Nigeria, are examined based on multi-year continuous observations using low-cost PM_2.5 sensors at six different sites. The average annual concentration of PM_2.5 across these sites was measured at 41.0 µg/m³, which surpassed both the Nigerian national air quality standard and the World Health Organization air quality guideline level. PM_2.5 levels were significantly higher during the dry season (November–March), often exceeding hazardous levels (over 350 µg/m³), than during the wet season. The analyses of trends in air mass trajectories and satellite data on fire occurrences imply that the transport of dust and accumulation of PM_2.5 originating from local/regional open burning activities played crucial roles in increased PM_2.5 concentrations during the dry season. Further, site-to-site variations in the PM_2.5 levels were observed, with relatively high concentrations at less urbanized sites, likely due to high local emissions from solid fuel combustion, waste burning, and unpaved road dust. Diurnal patterns showed morning and evening peaks at less urbanized sites, accounting for an estimated 51–77% of local emissions. These results highlight the importance of local emission sources in driving spatial–temporal PM_2.5 variations within the city and the need for targeted mitigation strategies to address the significant air pollution challenges in Akure and similar regional cities in West Africa.

Seasonal, diurnal, and site-to-site variations in indoor PM_2.5 concentrations in Akure, a city in southwestern Nigeria, are investigated by continuous observations using low-cost sensors in six households. Significant seasonal variations were observed, with the highest monthly PM_2.5 concentrations occurring in the dry season, both indoors and outdoors. Significant seasonal variations with higher PM_2.5 levels during the dry season were observed, with mean PM_2.5 concentrations of 55 μg/m³ in the kitchen and 48 μg/m³ in the living rooms, compared to those during the wet season (23 μg/m³ in the kitchen and 14 μg/m³ in the living rooms). The kitchen-to-outdoor and indoor-to-outdoor PM_2.5 ratios increased particularly during the morning and evening hours at several sites, suggesting significant contributions from cooking activities in the kitchen, as well as the transfer of PM_2.5 into the living room. An assessment of PM_2.5 exposure risks among 32 residents in the studied households revealed higher risks among individuals who cook routinely. This study underscores the importance of addressing indoor air pollution alongside outdoor pollution, particularly by improving ventilation and reducing cooking emissions, to effectively minimize exposure risks.

Particulate matter with aerodynamic diameters smaller than 2.5 µm, PM_2.5, is a problem for inhabitants globally. To address this problem, there is a need to know the amount of PM_2.5 present in the atmosphere. The quantification of PM_2.5 will help to determine the type of remedies for air quality. One of the employed quantification methods is the use of low-cost sensors, which are easy to use, have high temporal resolution, and are small to handle. In this study, we applied low-cost optical sensors to determine PM_2.5 during the dry (Harmattan) season at two sites in Akure, Ondo State, Nigeria. The results showed that PM_2.5 at one site (Site B) ranged between 14.4 and 590.4 µg/m³, whereas that at the other site (Site C) ranged between 14.5 and 737.2 µg/m³. The mean values (75.7 and 87.5 µg/m³ at Sites B and C, respectively) were significantly beyond the standard limits of World Health Organization and National Environmental Standards and Regulations Enforcement Agency in Nigeria. High daily average PM_2.5 concentrations were observed when the air masses coming from the northeast. Shorter timescale peaks within a few hours were frequently observed, especially at Site C during the daytime, attributable to the local emissions of PM_2.5 due to combustion activities. Higher-density multi-point observations are highly recommended to understand the sources, behaviors, and health effects of PM_2.5 in regional cities in South West Africa.