杭州地区大气CO2体积分数变化特征及影响因素

选取2015年8月至2016年9月杭州城区、远郊地区在线观测CO_2体积分数,分析杭州地区CO_2体积分数的城郊差异,并结合风向、CO_2体积分数周末效应、二十国集团(G20)峰会期间CO_2体积分数变化过程分析,探讨杭州城市对CO_2体积分数的影响程度.结果表明,杭州城区、远郊地区CO_2体积分数的日变化分布以单峰型形态为主,植物光合作用/呼吸作用和大气输送条件的日变化是主要的影响因素;城郊CO_2体积分数差值表现为双峰形态,人为排放对城郊CO_2体积分数差值的日变化分布存在重要影响.CO_2体积分数日变化幅度在春夏季节远郊地区大于城区,秋季则反之.杭州城区、远郊地区CO_2体积分数的季节变化趋势基本一致,均表现为冬、春季高,夏季低;城郊CO_2体积分数差值冬季最高,夏季最低.杭州地区CO_2体积分数高值的输送方向与周边城市区域的分布方向一致.杭州城区、远郊地区CO_2体积分数均呈现周末效应,尤其在城区,机动车排放对工作日-周末CO_2体积分数的日变化分布存在影响.杭州城区CO_2平均体积分数比远郊地区高9.3×10-6,G20峰会期间人为源排放的减少有效地降低了大气CO_2体积分数,尤其对市区的削减效果更为明显.

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.