Ten years of atmospheric methane observations at a high elevation site in Western China

摘要: Abstract In this paper, the continuous (1994–2001) and discrete air sample (1991–2001) measurements of atmospheric CH 4 from Waliguan Baseline Observatory located in western China (36°17′N, 100°54′E, 3816 m asl) are presented characterized. The time series show large episodic events on order 100 ppb throughout year. During spring, a diurnal cycle with average amplitude 7 ppb morning maximum late afternoon minimum is observed. winter, 14 ppb observed an minimum. Unlike most terrestrial observational sites, no obvious patterns present during summer or autumn. A background data selection procedure was developed based local horizontal vertical winds. selected hourly set representative “baseline” conditions derived approximately 50% valid data. range mixing ratios, annual means, increases mean at 1992–2001 were compared to samples collected other Northern Hemisphere sites. monthly means 1746–1822 ppb, 1786.7±10.8 ppb increase 4.5±4.2 ppb yr −1 inline sites between 30° 60°N. There variations that slightly different global pattern. shows unusual pattern two gentle peaks February along small valleys early winter spring peak-to-peak ∼11 ppb, much smaller than amplitudes mid- high-northern latitude strongly influenced by continental Asian emissions provide key information for models.