Abstract
Abstract. A 26-year, long-term record of atmospheric methane (CH4) measured in situ at the Mount Waliguan (WLG) station, the only World Meteorological Organization (WMO) and Global Atmosphere Watch (GAW) global station in inland Eurasia, is presented. Overall, a nearly continuous increase in atmospheric CH4 was observed at WLG, with a yearly growth rate of 5.1±0.1 parts per billion (ppb) per year during 1994–2019, except for some particular periods with near-zero or negative values, e.g., 1999–2000 and 2004–2006. The average CH4 mole fraction was only 1799.0±0.4 ppb in 1994 but increased to about 133 ppb and reached a historic level of 1932.0±0.1 ppb in 2019. The case study in the Tibetan Plateau showed that the atmospheric CH4 increased rapidly. During some special periods, it is even larger than that of city regions (e.g., 6.7±0.2 ppb yr−1 in 2003–2007). Generally, the characteristics of CH4 varied in different observing periods as follows: (i) the diurnal cycle has become apparent and the amplitudes of the diurnal or seasonal cycles increased over time; (ii) the wind sectors with elevated CH4 mole fractions switched from ENE-E-ESE-SE-SSE sectors (wind directions) in early periods to NNE-NE-ENE-E sectors in later years; (iii) the area of source regions increased as the years progressed, and strong sources shifted from northeast (city regions) to southwest (northern India); and (iv) the annual growth rates in recent years (e.g., 2008–2019) were significantly larger than those in the early periods (e.g., 1994–2007).
Highlights
Since the preindustrial era, the emission of greenhouse gases (GHGs) has increased continuously, and large increases have been found in recent years, with the concentration being higher than ever (WMO, 2019)
Compared with the global average mole fractions in recent years, i.e., 1853 ± 2 ppb in 2016, 1859 ± 2 ppb in 2017, and 1869 ± 2 ppb in 2018 (WMO, 2019, 2020), the atmospheric CH4 mole fractions at WLG are significantly higher. These results indicate that WLG has been affected by strong CH4 sources in recent years, which is possibly due to the influence of the two largest source regions of northern India and eastern China (Fang et al, 2013; Zhou et al, 2004)
Near-zero and even negative growth appeared in some periods, the overall CH4 increased rapidly, especially in recent years
Summary
The emission of greenhouse gases (GHGs) has increased continuously, and large increases have been found in recent years, with the concentration being higher than ever (WMO, 2019). The GHGs perturb the infrared radiation balance, which traps the heat in the atmosphere and contributes to global warming, melting glaciers and causing extreme weather events and many other global climate changes (IPCC, 2014). The recent 30-year span from 1983 to 2012 was the warmest of the last 800 years in the Northern Hemisphere, and half of the rising surface temperatures were due to increased GHG emissions (IPCC, 2014). As one of the most important GHGs, methane (CH4) has a global warming effect that is just less than carbon dioxide (CO2; Etminan et al, 2016). Liu et al.: Changing characteristics of atmospheric CH4 in the Tibetan Plateau
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