Spatial and temporal variations of the particulate size distribution and chemical composition over Ibadan, Nigeria.

Spatial and temporal variation of suspended particulate matter was measured in Ibadan, Nigeria during the raining and dry months of 2013 and 2014, respectively. Six different locations were considered, reflecting city-spread, population density, lifestyle, and vehicular- and industrial-related activities. Elemental characterisation of the samples were carried out using energy dispersive x-ray fluorescence (ED-XRF) spectroscopy, while the black carbon content was determined using an optical transmissometer. Backward trajectory analysis indicated that most air mass was of maritime origin except on few occasions that suggested the Sahara desert origin. Average PM2.5/PM10 ratio for the entire sampling period was 0.32 ± 0.04. This is slightly lower than the reported values in the coastal city of Lagos, partly because of more adequately paved and better road networks resulting in lower dust re-suspension and/or there are relatively finer fraction particulates from other sources, which might include marine, industrial, and secondary emission-related sources. Black carbon showed predominance in the fine fractions and was, majorly, of traffic origin. Major enriched elements of concern are S, Zn, As, and Pb aside from those of sea origin. Refuse burning was observed to be the principal source of Pb and Zn in all the sites except one, which showed major industrial-related activities source. This study will provide data for future measurement and modelling works as well as providing a benchmark for relevant agencies for policy making on setting emission standards for the country.