我国4个WMO/GAW本底站大气CH4浓度及变化特征

利用基于光腔衰荡光谱(CRDS)技术自组装的大气CH4在线观测系统,于2009～2010年在青海瓦里关、浙江临安、北京上甸子和黑龙江龙凤山这4个世界气象组织全球大气观测网(WMO/GAW)大气本底站对大气CH4进行了在线观测.临安站在所有季节中CH4浓度都表现出类似的日变化趋势,即浓度在每日～05:00(北京时间)达到最高值,在～14:00为最低.夏季龙凤山站CH4浓度表现出类似的规律,但其日变化振幅较大,达到216.8×10-9(摩尔分数,下同).上甸子站春、秋、冬季CH4浓度呈现类似变化趋势,但夏季日平均值较高,在晚间～20:00达到最高值,瓦里关站四季CH4浓度日变化均不明显.3个区域本底站(临安、上甸子和龙凤山)全年CH4本底浓度存在明显的变化,临安站CH4本底浓度在7月达到全年最低水平.龙凤山站则表现出相反的趋势,在8月达到全年最高值,其全年浓度表现出"W"型变化.冬季龙凤山和上甸子站CH4浓度高于春季和秋季.瓦里关站全年浓度变化较小,月平均浓度振幅仅为11.5×10-9.临安、上甸子和龙凤山3个区域本底站夏季CH4非本底数据占总数据的比例>70%.为分析气团传输的影响,对4站夏季高浓度时刻(瓦里关:CH4>1 870×10-9,龙凤山CH4>2 100×10-9,临安CH4>2 150×10-9,上甸子CH4>2 050×10-9)对应的气团轨迹进行聚类分析表明,夏季出现的高浓度CH4观测数据可能主要由气团传输所引起.

CH4 Concentrations and the Variation Characteristics at the Four WMO/GAW Background Stations in China

Background CH4 concentrations were continuously measured at the 4 WMO/GAW stations Waliguan in Qinghai(WLG),Lin’an in Zhejiang(LAN),Shangdianzi in Beijing(SDZ),and Longfengshan in Heilongjiang(LFS)] by Cavity Ring Down Spectroscopy system.From 2009 to 2010,the diurnal cycle of hourly average CH4 concentration at LAN was found to be similar in all four seasons,with the highest level detected at 05:00(Beijing Time) and the lowest at about 14:00.Similar CH4 diurnal cycles were observed at LFS in the summer time.However,the daily amplitude was much higher than that at LAN and reached 216.8×10-9(molar ratio).For SDZ station,there were similar trends in spring,autumn and winter.The daily average concentration in the summer was much higher than those of the other seasons and reached the highest at about 20:00.No apparent CH4 diurnal cycle was observed at the WLG station during the whole year.The seasonal variations were obvious at the three regional stations(LAN,SDZ,LFS).The background concentration was the lowest in July at LAN while reached the highest level in August at LFS.The yearly background concentration variation at LFS displayed a "W" pattern.At LFS and SDZ,the wintertime CH4 concentrations were higher than those in spring and autumn.WLG represented a clean area and its CH4 value was the lowest among the four stations with the monthly average amplitude to be about 11.5×10-9.At all three regional stations,non-background data accounted for more than 70% of the whole data.Cluster analysis of 3 day backward trajectories corresponding to the high CH4 concentration(WLG: CH4>1 870×10-9,LFS: CH4>2 100×10-9,LAN: CH4>2 150×10-9,SDZ: CH4>2 050×10-9) data points suggested that the high CH4 level measured in summer might be associated with the air mass transportation.