Assessment of source profiles for suspended particulate pollutants in Ibadan, Nigeria using positive matrix factorization

Abstract

Positive Matrix Factorization receptor model developed by the United States Environmental Protection Agency known as EPA PMF receptor model and reconstructed mass model were applied to air pollution data collected over Ibadan south west Nigeria. The essence was to determine the source profiles responsible for the high pollution level of Ibadan and to compare the sources resolved by these two methods. Particulate matter load was sampled over Ibadan, southwest Nigeria with the aid of low volume Gent air sampler, equipped with the Norwegian Institute for Air Research (NILU) Stacked Filter Unit (SFU). Two separate 47-mm nuclepore filters were mounted on the SFU to collect both fine and coarse particulates separately. Trace elements were determined using instrumental neutron activation analysis (INAA) and energy dispersive x-ray fluorescence (EDXRF) spectrometry. Five factors were resolved each for both fine and coarse fractions using EPA PMF. For the fine fraction, soil dust, vehicular emission, oil combustion, open burning and copper-rich source were the major sources of fine particulates over Ibadan city contributing 42, 16, 10, 22 and 10% respectively to the total aerosol loading over Ibadan. Vehicular emission, continental soil, sea salt, locally generated dust and copper-rich source were the sources identified for the coarse particulates. These contributed 7, 49, 13, 23 and 8% respectively. It was observed that emission from open burning was very high (22%), being the second largest contributor to the fine particulates. Reconstructed mass model showed good agreement with PMF in implicating soil dust as the major contributor of airborne pollutants over Ibadan. There was good correlation between the reconstructed mass and the measured mass with r² values of 0.87 and 0.98 for fine and coarse particulates respectively. The result of this work showed that re-suspended soil particulates were the major constituents of airborne particulate matter over Ibadan, with over 70 % contribution to the coarse mass and over 40 % contribution to the fine mass.

Keywords: Particulate Matter, Reconstructed mass, Refuse burning, PMF, Receptor model, Composite Variables