Source apportionment analyses for fine (PM_2.5) and coarse (PM_2.5–10) mode particulate matter (PM) measured in an urban area in southwestern Nigeria

To determine the influence of regional and local sources of the fine and coarse fractions of airborne particulate matter (PM), samples were collected in 2006, 2007, 2010, and 2013 covering the 2 major seasons (wet and dry) at multiple locations in Ile-Ife, Nigeria. A total of 216 samples for each of the PM_2.5 and PM_2.5–10 were collected on polycarbonate filters using low volume Gent samplers. Elements and black carbon was measured using x-ray fluorescence (XRF) spectrometry and optical transmissometry, respectively. The average mass concentration for the PM_2.5 and PM_2.5–10 at Obafemi Awolowo University (OAU) in 2006, 2007, and 2010 exceeded the annual National Ambient Air Quality Standards (NAAQS) of 15 and 60 μg/m³ for PM_2.5 and PM_2.5–10, respectively. At the Obafemi Awolowo University Teaching Hospital Complex (OAUTHC) sites, the PM_2.5 and PM_2.5–10 mass fractions also exceeded the NAAQS standards except at the urban background site. Positive matrix factorization (PMF) was used to identify and apportion the PM sources for the combined data from these sampling sites. Four sources each were identified for both PM_2.5 and PM_2.5–10. The sources are soil (44%), savannah burning (26%), scrap processing (18%) and vehicular emissions (12%) for PM_2.5 and soil plus biomass burning (71%), sea salt (22%), scrap processing (5%) and vehicle emissions (tire wear) (2%) for PM_2.5–10. Most of the PM mass originated from anthropogenic contributions. The highest contributions were associated with northwesterly wind from the urbanized areas of Ile-Ife.