中文摘要：

利用GC-ECD在线观测系统,在北京上甸子区域大气本底站开展了甲基氯仿（CH3CCl3）2年在线观测,利用逐步逼近回归法进行本底值筛分,讨论了上甸子站CH3CCl3浓度水平及其变化趋势.该站2009年和2010年的年均大气CH3CCl3本底浓度（摩尔分数,下同）分别为（9.03±0.53）×10^-12和（7.73±0.47）×10^-12,本底数据出现频率为61.1%（2009年）和60.4%（2010年）.上甸子站CH3CCl3浓度水平与北半球同纬度带本底站观测结果基本一致,低于文献报道的2001-2005年间我国华南区域和城市观测的结果.观测期间本底浓度呈下降趋势,下降率为1.39×10^-12a^-1.结合风向分析,该站CH3CCl3平均浓度最高的风向来自西南扇区,而平均浓度最低的风向来自东北扇区,不同风向的浓度差值分别为0.77×10^-12（2009年）和0.52×10^-12（2010年）.2010年各风向CH3CCl3平均浓度比2009年降低1.03×10^-12^-1.68×10^-12.

英文摘要：

An in-situ GC-ECD monitoring system was established at the Shangdianzi GAW regional background station（ SDZ） for a 2-year atmospheric methyl chloroform（ CH3CCl3） measurement experiment. Robust extraction of baseline signal filter was applied to the CH3CCl3time series to separate the background and pollution data. The yearly averaged background mixing ratios of atmospheric CH3CCl3were（ 9. 03 ± 0. 53） × 10- 12mol·mol^- 1in 2009 and（ 7. 73 ± 0. 47） × 10^- 12in 2010,and the percentages of the background data in the whole data were 61. 1% in 2009 and 60. 4% in 2010,respectively. The yearly background CH3CCl3mixing ratios at SDZ were consistent with the northern hemisphere background levels observed at Mace Head and Trinidad Head stations,but lower than the results observed at sites in southern China and some Chinese cities from 2001 to 2005. During the study period,background mixing ratios trends exhibited a decreasing rate of 1. 39 × 10^- 12a^- 1. The wind direction with the maximum CH3CCl3mixing ratio was from the southwest sector and that with the minimum ratio was from the northeast sector. The differences between the maximum and the minimum average mixing ratios in the 16 wind directions were 0. 77 × 10^- 12（ 2009） and 0.52 × 10^- 12（ 2010）. In the 16 different wind directions,the averaged mixing ratio of CH3CCl3in 2010 was lower than that in 2009 by 1. 03 × 10^- 12^-1. 68 × 10^- 12.