Temporal patterns of remote-sensed tropospheric carbon dioxide and methane over an urban site in Malawi, Southeast Africa: Implications for climate effects

Abstract

Carbon dioxide (CO2) and Methane (CH4) are considered the most crucial climate forcing greenhouse gases due to their significant impacts on climate systems. The present study is aimed at analyzing the long-term (2004–2016) concentration patterns of CO2 and CH4 over Malawi located in Southeast Africa using the observations from Atmospheric Infrared Sounding (AIRS). The study found an annual increase concentration of CO2 and CH4, with a rate of 7.08% and 1.66%, respectively; whereas, the respective concentration levels of CO2 and CH4 in 2016 were noted as >400 ppm and >750 ppb, which is comparable to that reported by IPCC (2014) over the globe. The monthly and seasonal analyses revealed that high patterns are associated with biomass burning season, changes in vegetation cover, and long-range transport. The two trace gases were seasonally correlated with carbon-containing compounds produced from incomplete combustion and biomass burning. The trace gases and pollutants are emitted from the burning of crop residues during the harvesting season, besides, open burning of forests and vehicular emissions. The present study also detected a seasonal increase in CO2 and CH4 concentrations during JJA and SON seasons. The temperature (T °C) exhibited profound correlation with CO2 (r = 0.75, p < 0.01) and CH4 (r = 0.80, p < 0.01) during the pollution peak season of SON. Moreover, CO2 and CH4 showed significant positive correlation with cloud top temperature (r = 0.56, p < 0.05 and r = 0.74, p < 0.01, respectively) and negative correlation with cloud fraction (r = −0.55, p < 0.05 and r = −0.69, p < 0.01, respectively) during SON, imply extensive climatic effect by the trace gases during high pollution season. The backward air mass trajectories divulge a contribution of distant produced pollutants from neighboring Mozambique, Madagascar Islands, and the South American continent. The major sinks of tropospheric CO2 and CH4 observed from the present study are precipitation and vegetation.