北京城区二氧化碳浓度和通量的梯度变化特征——I浓度与虚温

根据北京塔7层涡动系统2012年5月至2013年12月的湍流观测数据,分析了北京城区二氧化碳浓度在不同高度层次的日变化和月变化特征,并初步给出不同季节和日变化时间段内二氧化碳的浓度垂直廓线.结果表明:二氧化碳浓度整体随高度而下降;各观测层均有浓度的明显日变化,夏季最为明显,冬季相对平缓;近地层浓度直接受城市供暖、地表植被、交通运输等碳源影响,更高观测层浓度则受对流输送和天气过程影响较大;垂直方向上,冬季浓度变化范围最大,夏季层间浓度变化最明显;在一天中的任何时刻,近地面层二氧化碳浓度的日变化最低值一般出现在夏季,50m以上则出现在春季,浓度最高值总是出现在冬季;根据对二氧化碳浓度四季垂直廓线变化的分析可以看出,边界层二氧化碳浓度强烈受到碳源、下垫面植被、大气稳定度、环境温度和天气过程等因素的影响.

Gradient characteristics of CO2 concentration and flux in Beijing urban area part I: Concentration and virtual temperature

As one of the most important green house gas discharged by human daily activities, CO₂ concentration in urban area showed a significant augment tendency in recent years, and most of it is produced by burning fossil fuels and vehicle exhaust emission. With the turbulence data measured by open path eddy covariance system of Beijing 325m metrological tower, CO₂ concentration at 7 different heights were measured from May 2012 to December 2013. Based on the collected data, the seasonal and diurnal variation of CO₂ concentration was analyzed, also the vertical profile in different season and certain time of day.#br#To analyze horizontal and vertical CO₂ concentration and flux characters in Beijing urban area, 7 open path eddy covariance (EC) systems were built in Beijing 325 m Meteorology Tower in May 2012. Up to now, the systems have collected CO₂, H₂O, and Wind field data of 10 Hz for 36 months. EC method is now the predominant technique for the fluxes measurement and analysis. As the urban surface structure is too complex to adapt EC's theoretical assumption, we have to make a series of corrections to obtain rather accurate and representative fluxes data to assure the validity and authenticity of study result. EDIRE and IAP-FLUX were used for flux data processing. The previous one was approval by Global FLUXNET and latter one was developed by author's group which was proved to have a good performance in data processing. IAP-FLUX form by three parts and more details will be given in the paper.#br#According to the analysis of data from May 2012 to December 2013, the results indicate that: ① CO₂ yearly averaged concentration value decreases with height, and has an inverse relation with temperature. Its maximum value appears in winter by reason of vegetation withering, city heating and enhanced inversion; and the minimum value appears in summer due to the influence of strong convection system and vegetation carbon sequestration. Overall, CO₂ concentration shows a generally uniform vertical distribution with about 10% difference between 8m and 280m level in summer and 6.8% in winter respectively. ② At all observation heights, the diurnal variation of CO₂ concentration displayed a very clear cycle with double peaks corresponding to city morning and evening transportation rush time. City heating must be considered in winter as it reduced the variation of concentration and lead to a relatively flat diurnal variation. ③ Take many factors into consideration, we can conclude that in the area close to ground, CO₂ concentration was more strongly influenced by urban heating, vehicles transportations, surface vegetation distribution, etc. Its minimum value appears in summer and maximum in winter no matter at daytime or nighttime. While the other levels' concentrations are more affected by thermal convection or weather process, their extreme values appear in spring and winter respectively. ④ The vertical distribution type of CO₂ concentration was different with season and certain time of day. Combination of nature and artificial factors, CO₂ concentration in urban boundary layer was strongly affected by surface carbon emission source, underlying surface vegetation, atmospheric stability and weather process. ⑤ Urban heating conducted an obvious and average augment in vertical distribution of CO₂ concentration about 6% to 7%. Both concentration and flux is highly impacted by human activities. Beijing urban atmospheric CO₂ is a net emission source.#br#Concentration of carbon dioxide in the atmosphere reflects the degree of human consumption of fossil fuels. Combustion products of fossil fuel can seriously affect the air quality. Beijing is one of the fastest growing and urbanizing cities throughout the country, and one of the cities with carbon emissions increasing dramatically and temperature rising sharply in the worldwide. By analyzing the data of Beijing Tower, we could see that urban CO₂ concentration and its distribution exhibit a fractal characteristic and was affected obviously by human activity. This work is helpful for understanding the impact of artificial activities on the urban green house gas concentration and atmospheric environmental quality, as well as indicating the way to improve Beijing's air quality based on scientific research.