Temperature, Humidity and Air Pollution Relationships during a Period of Rainy and Dry Seasons in Lagos, West Africa

Air pollution is a concern in the West Africa region where it is known that meteorological parameters such as ambient temperature and humidity can affect the particulate matter loading through atmospheric convection and dry deposition. In this study, we extend the investigation of these relationships to particulate matter less than 1 µm in diameter (PM1), nitrogen dioxide (NO2), nitrogen monoxide (NO) and ozone (O3), for a complete period of rainy and dry seasons in Lagos. Regression analysis of the results indicate that there is a negligible to weak correlation (r < 0.39) between the temperature, humidity and air pollutants during the year, except for NO2 and O3 which respond moderately to humidity during the dry season, an observation previously unreported. The mean monthly values for all the air pollutants are lower during the rainy season compared to the dry season, indicating a potential higher contribution of the transport of pollutants from the north-eastern desert regions and the reduction of the wet removal of particles during the dry season. The World Health Organization air quality guidelines are mostly exceeded for fine particles with diameters less than 2.5 µm (PM2.5), supporting previous studies, as well as for the NO2 concentration levels. As PM2.5 contributes to at least 70% of the particulate matter pollution throughout the year, policy guidelines could be enacted for people with chronic respiratory issues during the January/February months of intense high air pollution, high temperature but low humidity values.