Study on the concentration variation and impact factors of CH₄ in Jinsha atmospheric background station

Based on the observation data of CH₄ concentrations and meteorological parameters from 2007 to 2021 in Jinsha station,an atmospheric background station in central China,were used to investigate the variations of CH₄ concentrations and the influencing factors.CH₄ concentrations in Jinsha station increased significantly after 2010 with a higher increasing trend and larger monthly fluctuations than that in Waliguan station.The original concentrations of CH₄ were 2093.9×10^-9 and 2096.6×10^-9,and the background concentrations were 2068.7×10^-9 and 2083.0×10^-9 in 2020 and 2021,respectively.After REBS (robust extraction of baseline signal) filtering,the ratios between original and background concentrations in summer were lower than those in winter and spring,revealing the significant impact of regional transport on CH₄ background concentrations in Jinsha.The emission of CH₄ in the lake agglomeration of Jianghan Plain peaked in summer and autumn.Under the influence of transport delay and chemical reaction,CH₄ concentrations in Jinsha ranked in the order of autumn>winter>summer>spring,with the highest values in September and October.The diurnal variation of CH₄ was in bimodal distribution and the highest values occurred at 08:00-09:00 and 18:00-20:00.Influenced by meteorological factors such as temperature and humidity,CH₄ concentrations peaked at the temperature of 20-25 ℃ and in the wind direction of westerly and northerly,decreasing with enhancing wind speed and descending humidity.CH₄ concentrations in Jinsha station were affected by short-distance transport.The northern air mass from Shaanxi and Henan provinces has the greatest contribution in spring and winter,leading to the highest CH₄ concentrations in Jinsha,while the air mass from Jiangxi province accounted for the highest proportion in summer and the inner-province short-distance transport was predominant in autumn.