[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.