Measurement report: Changing characteristics of atmospheric CH<sub>4</sub> in the Tibetan Plateau: records from 1994 to 2019 at the Mount Waliguan station
<p>A 26-year, long-term record of atmospheric methane (<span class="inline-formula">CH<sub>4</sub></span>) measured in situ at the Mount Waliguan (WLG) station, the only World Meteorological Organization (WMO) and Global Atmosphere Watch (GAW) global station i...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/393/2021/acp-21-393-2021.pdf |
| Summary: | <p>A 26-year, long-term record of atmospheric methane (<span class="inline-formula">CH<sub>4</sub></span>) 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 <span class="inline-formula">CH<sub>4</sub></span> was observed at WLG, with a yearly growth rate of <span class="inline-formula">5.1±0.1</span> 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 <span class="inline-formula">CH<sub>4</sub></span> mole fraction was only <span class="inline-formula">1799.0±0.4</span> ppb in 1994 but increased to about 133 ppb and reached a historic level of <span class="inline-formula">1932.0±0.1</span> ppb in 2019. The case study in the Tibetan Plateau showed that the atmospheric <span class="inline-formula">CH<sub>4</sub></span> increased rapidly. During some special periods, it is even larger than that of city regions (e.g., <span class="inline-formula">6.7±0.2</span> ppb yr<span class="inline-formula"><sup>−1</sup></span> in 2003–2007). Generally, the characteristics of <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span> 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).</p> |
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| ISSN: | 1680-7316 1680-7324 |