Atmospheric CO2 and CH4 observations in Hangzhou before, during, and after the 2023 Asian Games: Insights from vehicle-carried and fixed stations

On the basis of the vehicle-carried mobile observation method, we conducted CO₂ and CH₄ observations in Hangzhou city during different periods before, during and after the Asian Games in autumn 2023. Both the difference between urban and rural monitoring station data and the difference between mobile observation and urban background station data during the period of emission reduction implementation were used as quantitative indicators of policy effectiveness. The differences in the CO₂ and CH₄ concentrations between the mobile observations and the background values exhibited the order of during the Asian Games < before the Asian Games < after the Asian Games, and the differences between the urban and rural observation station values decreased during the Asian Games, indicating the effectiveness of the emission reduction measures. Additionally, the differences in the CO₂ and CH₄ concentrations between the mobile observations and background values revealed different spatial variation characteristics before, during and after the Asian Games. This demonstrates that emission reduction measures do not yield exactly the same effectiveness for greenhouse gases from diverse emission sources. Moreover, the wind speed, wind direction and boundary layer height may negatively affect the effectiveness of emission reduction. To obtain better results, emission reduction measures must continue over a longer period.