IMPACTOF LOCAL SURFACE WINDS ON ATMOSPHERICMETHANE BACKGROUND CONCENTRATIONS AT MT.WALIGUAN

In combination with partitioned continuous data sets of atmospheric CH₄ and local surface winds corresponding to different seasons from July 1994 to December 1996, the impact of surface winds on the CH₄ background concentrations at Mt. Waliguan (36° 17′N, 100° 54′E, 3816 m ASL) in the western China was studied, which is one 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 CH₄ variations. Horizontal wind direction of NE—ENE—E is the major non-background section of atmospheric CH₄ observation at the site. Horizontal wind speed larger than 10m/s, or calm condition, or vertical wind speed larger than±1 m/s has maximum impact on CH₄ hourly mixing ratios. Statistical analysis also gives the averaged CH₄ 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 CH₄ 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.