Variation Trend of Greenhouse Gases CO2 and CH4 in Hefei, China

This study investigates the spatial and temporal dynamics of carbon dioxide (CO₂) and methane (CH₄) in the Hefei region from 2009 to 2020 using satellite-based column ob-servations (GOSAT) and the HYSPLIT model. The results reveal a significant increasing trend for both greenhouse gases, with Hefei's CO₂ growth rate (2.43 ppm/year) exceed-ing the global average. Pronounced seasonal cycles were identified: CO₂ concentrations peak in winter due to enhanced fossil fuel combustion for heating and weakened plant photosynthesis, and reach a minimum in summer owing to strong biospheric carbon uptake. In contrast, CH₄ concentrations are highest in summer and autumn, likely driven by agricultural activities such as rice cultivation, and lowest in winter and spring. Diurnal variations show a synchronous pattern for CO₂ and CH₄, peaking around noon, influenced by the interplay of anthropogenic emission cycles and plane-tary boundary layer dynamics. Backward trajectory analysis and clustering further elu-cidate that the transport pathways and source regions of greenhouse gases are domi-nantly controlled by the East Asian monsoon. The summer is characterized by clean, locally-influenced marine air masses, while the winter is predominantly influenced by long-range transport from the polluted northwestern interior of China, which acts as a critical pollution corridor. This research underscores the combined roles of local an-thropogenic activities, regional transport, and meteorological systems in driving the characteristics of greenhouse gases in an inland subtropical city.