Variability of greenhouse gases in Lagos: CO2, CH4, N2O and halocarbons in a developing Western Africa megacity

Greenhouse gas (GHG) emissions significantly affect climate change, public health, and the environment. Lagos, a developing megacity with a bustling economy and growing population, contributes substantially to GHG concentrations through intensive energy consumption and material use. This study investigated the temporal and spatial distributions of key ambient GHGs across Lagos, Nigeria, from August 2020 to July 2021, including carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), and halocarbons (chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons). Using data from a network of six sampling stations, the relationships among these GHGs and their concentrations in relation to urban emissions were analyzed. Our findings identified distinct seasonal variability in GHG concentrations driven by urban activities and meteorological conditions. CO₂ concentrations ranged from 455 to 484 ppmv, with peak values at the IKO and NCF stations. CH₄ concentrations reached a maximum of 2210 ppbv, primarily attributed to waste management activities, while N₂O showed minimal variations suggesting limited local sources. Halocarbon concentrations peaked during the dry season due to increased air conditioning use and industrial activities. Alternatively, CO₂, N₂O, and CH₄ were highest during the wet season (April to July), influenced by increased vehicular emissions and enhanced waste decomposition in waterlogged landfills. The study identified transportation, waste management, and refrigeration as the primary GHG sources in Lagos. The observed correlations between halocarbons and other GHGs underscore the interconnected nature of urban emissions sources. These findings provide valuable insights for policymakers and stakeholders to develop targeted mitigation strategies for reducing GHG emissions in rapidly urbanizing megacities.