Characteristics of and Factors Affecting Atmospheric CO2 Concentration in Hangzhou

: In situ measurement of CO2 concentration(volume fraction) was carried out in both urban and rural areas of Hangzhou from August 2015 to September 2016. The characteristics of CO2 concentration at the urban site were compared to those at the rural site, and the factors affecting CO2 concentration in Hangzhou were analyzed via wind direction, weekday-weekend difference in CO2 concentration, and evolution of CO2 concentration during the G20 summit. The results revealed that the diurnal variation of CO2 concentration in both the urban and rural areas presented a single peak curve most of the time, which resulted from the daily evolution of plant photosynthesis/respiration and atmospheric transport conditions. The diurnal variation of the difference in CO2 concentration observed at the urban and rural sites showed a bimodal peak curve, because anthropogenic emissions played a more important role. The diurnal amplitude of CO2 concentration in rural area was higher than that in urban area in spring and summer, but lower in autumn. The seasonal variation of CO2 concentration in both the urban and rural areas showed the same trend, with higher values appearing in winter and spring and lower values in summer. The difference in CO2 concentration observed at the urban and rural sites reached its highest level in winter, and dropped to its lowest in summer. The wind direction induction of high CO2 concentration was consistent with the location of the surrounding urban areas. A weekday-weekend difference in CO2 concentration was observed in Hangzhou, especially in urban area, as traffic emissions had an impact on the weekday-weekend difference in diurnal distribution of CO2 concentration. The average volume fraction of CO2 in urban area of Hangzhou was 9.3×10-6 higher than that in rural area, and the reduction of anthropogenic emissions during the G20 summit reduced the atmospheric CO2 concentration effectively, especially in urban area.