Tropical Air Chemistry in Lagos, Nigeria

Abedola Odu-Onikosi, Pierre Herckes, Matthew Fraser, PHILIP K. HOPKE, John Ondov, Paul Solomon, Olalekan Popoola, George Hidy, EnvironQuest

     Abstract Number: 312
     Working Group: Urban Aerosols

Abstract
The Nigerian city of Lagos experiences atmospheric photochemistry and aerosol chemistry as a consequence of severe air pollution. A study covering a year between August 2020 and July 2021 included measurements of gas-phase and aerosol processes, with surface meteorology at six urban sites. The sites were selected to represent near sea coast conditions inland towards the agricultural and grasslands of Nigeria. The observations included continuous concentrations for CO, SO2, NOx, VOC, O3, PM2.5 and PM10. Samples were collected and analyzed for speciated VOC, and particulate chemical composition including inorganics and organics. The average diel variations in concentrations indicated well-known local photochemistry resulting from the presence of combustion sources, including motor vehicles, petroleum production and use, and open burning. The annual diel characteristics were emission dependent and modulated by meteorological variability, including the sea breeze and the seasonal changes associated with monsoon and Harmattan winds. Gases and particulate matter varied daily with the onset of source activities during the day. For fine particles less than 2.5 micrometers in diameter (PM2.5), source emissions into the air included those affected by the photochemical cycle. Importantly, particle sources included a large component of dust and carbonaceous material. For the latter, there was evidence that particle concentrations were dominated by primary sources, with little secondary material formed in the atmosphere. From complementary studies, there were occasions when regional chemical processes affected the local conditions, including transportation, industry, commercial activity and open waste burning.