北京城市地区CO2通量特征

城市CO₂排放是全球大气CO₂的重要来源. 为探讨不同气象背景条件、土地利用方式和覆盖类型以及能源消耗方式对城市CO₂排放的影响,利用北京325m气象塔(39°58′N、116°22′E)上140m高涡动相关仪监测的湍流数据,对2009年6月26日—2011年12月31日气象塔周边区域共919d CO₂通量的时间变化及方向分布特征进行了研究,并计算了CO₂的年排放量. 结果表明:CO₂通量受交通因素影响明显,各季节CO₂通量日间早、晚峰值出现时间与车流量高峰时间一致,该特征在冬季表现尤为突出. 冬季取暖会显著增加CO₂排放量；受供暖排放和植物休眠的影响,冬季CO₂通量全天均高于其他季节,日均值为30.1μmol/(m2·s),显著高于春、夏、秋三季的15.2、17.9和15.8μmol/(m2·s) (t-test,P<0.001). CO₂通量在不同方向的分布特征表明,其值与源区内人工建筑面积所占比例成正比；而在植被覆盖比例较高的方位,其CO₂通量相应较小. 气象塔周边区域CO₂年均排放量达到30.0kg/(m2·a),但仍小于伦敦的35.5kg/(m2·a). 

Study of Carbon Dioxide Flux Characteristics over an Urban Area in Beijing

Urban area is a significant contributor to the global carbon dioxide emissions. In order to understand the influences of meteorological background conditions, land use and land cover, as well as energy consumption on urban CO_2emission, temporal and spatial distribution characteristics and annual emissions were analyzed, based on observed data obtained by eddy-covariance measurements at 140m above the ground on Beijing Meteorological Tower in a high-density residential area from June 26th, 2009to December 31st, 2011.The results showed that the diurnal patterns of CO_2were largely influenced by traffic volume and typical two-peak traffic patterns. Moreover, the influence was particularly prominent in winter, since fuel consumption for heating during winter considerably enhances CO_2emission. Due to heating and plant dormancy, the daily average flux measured in winter (30μmol/(m2·s)) was significantly higher than those in other seasons with 15.2,7.9and 15.8μmol/(m2·s) in spring, summer and autumn, respectively (t-test, P<0.001). Spatial variation patterns of CO_2flux were mainly determined by the prevailing surface cover within the flux source area, that higher CO_2values coming from a higher proportion of man-made surfaces and lower CO_2values be accompanied by highly vegetated area within flux source areas. The study site was a net source of CO_2in the atmosphere and the total annual averaged CO₂emissions from the neighborhood of the tower were estimated to be 30.0kg/(m2·a), which was lower than that of 35.5kg/(m2·a) in London. The results would be helpful for understanding the role and function of urban ecosystems in the global carbon cycle, and can provide a reference material for the future urban development planning, in order to reduce the adverse effects of urban sprawl on climate.