地面风对瓦里关山大气CH_4本底浓度的影响分析

IMPACT OF LOCAL SURFACE WINDS ON ATMOSPHERIC METHANE BACKGROUND CONCENTRATIONS AT MT. WALIGUAN

使用 1 994年 7月至 1 996年 1 2月大气CH4和地面风现场连续观测资料 ,分析了瓦里关全球大气本底基准站 ( 36°1 7′N ,1 0 0°5 4′E ,海拔 381 6m)地面风变化对大气CH4本底浓度的影响。结果表明 ,水平风向、风速和垂直风向、风速的变化对大气CH4观测值的影响在春、夏、秋、冬季有明显不同 ,水平风向NE—ENE—E为CH4测量最主要的局地影响非本底扇区 ,静风及水平风速大于 1 0m/s、垂直风速大于± 1m/s对观测结果都有较大影响 ;由观测事实的统计平均还给出了此段期间瓦里关大气CH4在不同季节的浓度分布范围和日变化类型 ,并分析了可能成因 ;将地面风数据作为大气CH4本底资料的过滤因子之一 ,提出了适用于不同使用目的和要求的我国内陆高原大气CH4本底数据筛选方法 ,本底数据留存率约为原始资料量的 5 0 %

In combination with partitioned continuous data sets of atmospheric CH 4 and local surface winds corresponding to different seasons from July 1994 to December 1996, the impact of surface winds on the CH 4 background concentrations at Mt. Waliguan (36°17′N, 100°54′E, 3816 m ASL) in the western China was studied, which is one of the global atmospheric baseline monitoring stations. Results indicate that the variability in the horizontal and vertical wind speed/direction over the periods of different seasons has a distinct impact on the observed CH 4 variations. Horizontal wind direction of NE-ENE-E is the major non-background section of atmospheric CH 4 observation at the site. Horizontal wind speed larger than 10 m/s, or calm condition, or vertical wind speed larger than ±1 m/s has maximum impact on CH 4 hourly mixing ratios. Statistical analysis also gives the averaged CH 4 distribution and its diurnal variation pattern in different seasons during this period. By using the local surface winds outcomes as one of the data filters for the atmospheric CH 4 observed concentrations at in-land plateau of China, the selection procedures of background concentrations were provided for the applications to the different purpose and requirements. The selected hourly data sets representing 'baseline' conditions accounts for 50% of the raw records approximately.