The impact of local winds and long-range transport on the continuous carbon dioxide record at Mount Waliguan, China

This paper describes the continuous measurements of atmospheric carbon dioxide at Mt. Waliguan (36degrees17'N, 100degrees54'E, 3816 m asl) in western China over the period 1994-2000. The CO2 hourly mixing ratios were segregated by horizontal wind direction/speed and vertical winds, respectively, merged by season over the entire measurement period. The short-term variability in CO2 was examined mainly from the point of view of local winds observed at this station and isobaric back trajectory cluster-concentration analysis as for local and long-range transport influence, to permit the selection of hourly average data that is representative of background conditions. From the selected hourly data, daily, monthly and annual averages that are not influenced by local CO2 sources and sinks be computed by discriminating the local and regional impact on the Waliguan CO2 records. On the basis of these results, background CO2 data were then analyzed to evaluate the averaged diurnal variation, monthly mean time series, CO2 mixing ratio distribution in different seasons as well as averaged seasonal cycle. Annual mean and growth rate of CO2 at Waliguan during the period of 1991 to 2000 were further discussed by supplement with NOAA/CMDL flask air sampling records at this station and other monitoring stations located at similar latitudinal band in the Northern Hemisphere. The results from this study can provide atmospheric CO2 characteristics in Asian inland regions, and be used in other studies to improve the understanding of carbon source and sink distributions.