北京上甸子区域大气本底站四氯化碳(CCl_4)在线观测

利用自组装GC-ECD系统在北京上甸子区域大气本底站开展大气四氯化碳(CCl4)摩尔分数在线观测.2007年4月～2008年3月期间,该站CCl4本底摩尔分数(89.4±0.7)×10-12,与北半球同纬度带Mace Head和Trinidad Head本底站观测结果基本一致;非本底摩尔分数(94.7±5.1)×10-12,出现频率63.6%,表明该站也能捕捉到高摩尔分数CCl4空气团输送信息;CCl4本底摩尔分数变化较小,且没有明显的季节变化;非本底摩尔分数呈现夏高冬低的特点,平均非本底摩尔分数最高月份(6月)比最低月份(1月)高7.6×10-12.应用CO比值相关法初步估算2007年4月～2008年3月我国CCl4排放量约4.7kt·a-1,与文献报道Bottom-up方法估算我国同期CCl4排放量接近;CO比值相关法估算CCl4排放量的不确定性主要来自同源假设及观测站代表性.

In-situ measurement of atmospheric carbon tetrachloride(CCl4) at the Shangdianzi Global Atmosphere Watch regional station

A gas chromatography-electron capture detector (GC-ECD) system was established at the Shangdianzi GAW (Global Atmosphere Watch) regional station for in-situ measurement of atmospheric carbon tetrachloride mixing ratios. From April 2007 to March 2008, the background CCl4 mixing ratio was (89.4±0.7)×10-12 mol·mol-1, close to the northern hemisphere background level observed at the Mace Head and the Trinidad Head stations. The polluted CCl4 mixing ratio was (94.7±5.1)×10-12 primarily due to anthropogenic emission from various regions and air mass transport. There was no significant seasonal variability of the background CCl4 data. However, the polluted data was much higher in summer than in winter, elevated up to 7.6×10-12. Good correlation was observed between the enhanced CCl4 and the enhanced CO mixing ratios. A CO tracer-ratio method was applied to estimate the CCl4 emission from China during the study period. The estimated CCl4 emission was 4.7 kt·a-1 using the CO tracer-ratio method, which was close to the literature result obtained by the bottom-up method. Uncertainty of the emission estimate comes mainly from the homologous source assumption and station representativeness.