苏南地区CO2本底浓度及源汇特征

基于2015~2018年苏州张家港站CO₂在线观测数据，采用时序检查、选取稳定性数据、异常值剔除等质量控制方法获得可靠数据，并通过平均移动过滤（MAF）本底筛分法获得本底数据，讨论苏南地区CO₂变化特征.结果发现：CO₂本底浓度日变化为单峰结构，谷值和峰值分别出现在下午15：00和凌晨5：00前后；季节变化为双峰结构，峰值分别出现在12月和4月；日、季节变化的分布特征均与陆地生态系统、气象条件和人类活动有关.此外，2015~2018年CO₂浓度呈逐年上升趋势，抬升浓度占比逐年增加，吸收浓度占比波动较小，表明人类活动对CO₂浓度的影响正在逐年增加；而陆地生态系统对CO₂吸收汇的作用则相对稳定.源汇分析显示，CO₂抬升浓度随季节小幅波动；吸收浓度则夏半年较低，冬半年较高；抬升浓度日变化为单峰结构，谷值和峰值分别出现在15：00和8：00前后，早晨正值上班高峰，机动车排放可能为早晨峰值的主要因素；吸收浓度日间低、夜间高，这主要与植物光合作用及对流输送有关.分析CO₂浓度与风的关系发现，所有季节静风情况下，CO₂浓度偏高均最为明显，大部分方向CO₂浓度高低与风速大小有明显的负相关，其中S~WNW方向偏高最为明显，这可能是因为SW~NW方向主要为内陆城市群，且测站周边建筑区主要位于W~N方向，弱风有利于本地排放累积的结果.此外，WNW方向风速较大时浓度仍偏高明显，可能与测站W~N方向为建筑区及内陆城市群有关；而测站偏东方向主要为农田和林区，受人类活动影响较小，且海上气流较为洁净，故偏东风较弱时浓度也不高；说明了CO₂浓度除了与风速大小有关外，与周边下垫面类型及较远距离环境特征（城市群或海洋）也有一定的关系.

A study on background concentration and source-sink characteristics of CO2 in south of Jiangsu

By quality control methods (i.e., time series inspection, selection of stability data and eliminating the abnormal values), high-quality CO₂ datasets of Zhangjiagang Station in Suzhou from 2015 to 2018 were obtained to study the background concentration and source-sink characteristics of CO₂ in Suzhou. By Moving Average Filtering (MAF) method, CO₂ datasets have been separated as background and non-background data. The background data showed that the diurnal variation of CO₂ background concentration showed a single peak structure, and the peak and valley value was around 5:00 a.m. and 15:00 p.m, respectively. The seasonal variation showed a double peak structure, with the peaks in December and April. Both of the distribution of daily and seasonal variation of CO₂ were related to terrestrial ecosystems, meteorological conditions and human activities. From 2015 to 2018, the CO₂ concentration has increased. Particularly, the proportion of rising concentration has significantly increased, which may due to the human activities. On the contrast, the variation of the absorption concentration was stable, which inferred that the role of terrestrial ecosystem on CO₂ concentration was relatively stable. The source-sink analysis showed that, seasonally, the CO₂ uplifting concentration fluctuated slightly, while the absorption concentration showed remarkable seasonally variations. The diurnal variation of the rising concentration was a single-peak structure, with the peak value around 8:00 a.m., which may be traced to the high motor vehicle emissions in the morning. The absorption concentration was low in the daytime and high in the nighttime, which may be related to the plant photosynthesis and convective transport. We further analyzed the relationship between the CO₂ concentration and the wind field. The high CO₂ concentration has prevailed under the condition of calm wind in all seasons. Generally, in most wind directions, the concentration of CO₂ was negatively correlated with the wind speed. Particularly, the high CO₂ concentration was mostly accompanied at south to west-northwest winds. This may due to that the inland urban agglomeration was mainly located in southwest to northwest direction, and the construction area around the station was mainly located in southwest to north direction. Consequently, weak winds would lead to cumulative local emissions. However, the concentration of CO₂ was high at west-northwest winds. This may due to that the building area and inland urban agglomeration was in the west to north direction of the station. As the wind blew eastward, the concentration was low even when the wind is small, because the air from the sea is relatively clean.Moreover, the farmland and forest areas were mainly located in the east of the station, which was less affected by human activities. Our results have suggested that the concentration of CO₂ was not only related to the wind speed, but also related to the type of underlying surface and the long-distance environmental characteristics.