Source Contributions to Nigerias Atmospheric O3, CO and NO2 Concentrations and the Impact on Africa

Poor air quality impacts human health, especially in developing nations where pollutants are a consequence of increased population and socioeconomic developments, and where a weak understanding of emission inventories in the region contributes to uncertainty in mitigation efforts. This presentation aims to reduce this uncertainty and is a step towards improving air quality for the region. The community atmosphere model Version 6 with chemistry (CAM6-chem) at 1-degree horizontal resolution was configured with different emissions inventories, the coupled model inter-comparison project (CMIP-6) and the diffuse inefficient combustion emissions specific to Africa (DICE-WA), to quantify the sectoral anthropogenic emission contributions of different tracers to total emissions in tropical West Africa (WA). Results show black carbon (BC) has the largest contribution of 0.20 Tg/yr from the residential sector when using DICE-WA, and the highest emissions of BC are seen from the model over Nigeria. Carbon monoxide (CO) emissions also show the largest contribution from the residential sector when using DICE-WA (12.04 Tg/yr) or CMIP-6 (23.12 Tg/yr). Satellite observations of ozone (2013) from the tropospheric emission spectrometer (TES) on board the AURA satellite over Lagos was also compared with CAM6-chem ozone simulations. Results show that when compared to the TES maximum average value of 62 ppb ozone is ~50% lower using DICE-WA and ~33% lower with CMIP6 emissions. In addition, we carried out a sensitivity test of the local Nigerian anthropogenic emissions contribution to O3, CO and NO2, while setting all anthropogenic emissions over West Africa to zero. We found that local emissions were responsible for 15 ppb of the dry season (January) O3 maximum of 45 ppb over Nigeria. Local contributions to CO and NO2 in the dry season were 30 ppb and 3 ppb, respectively. For the wet season (July), O3 concentration were reduced and the local emission contributions to the O3 maximum drops to 10 ppb, but no changes were observed for CO and NO2. Similarities in CO in the sensitivity simulations shows the regional extent of the contribution of Nigerian anthropogenic emissions to African atmospheric composition.