Characteristics and source analysis of greenhouse gas concentration changes at Akedala Station in Central Asia

Abstract

Mole fractions of atmospheric carbon dioxide (CO 2 ), methane (CH 4 ) ,nitrous oxide (N 2 O) and sulphur hexa uoride (SF 6 ) have been continuously measured since September 2009 at the Akdala station (47˚06′N, 87˚58′E, 563.3 masl) in China. The station is located in the Central Asia and northwest of China, and it is the only station in that region with background conditions for long-term greenhouse gas observations. Characteristics of the mole fractions, growth rates as well as in uence of long-distance transport were studied considering data from September 2009 to December 2019. The greenhouse gases concentrations at Akedala Station show a trend of year-on-year growth, with CO 2 concentrations ranging from 389.80×10 -6 to 408.79×10 -6 (molar fraction of substances, same below), CH 4 concentrations ranging from1890.07×10 -9 to 1976.32×10 -9 , N 2 O concentrations ranging from 321.26×10 -9 to 332.03×10 -9 , and SF 6 concentrations ranging from 7.04×10 -12 to 10.07×10 -12 , the growth rate of which is similar to the decadal average growth rate in the northern hemisphere. There exist obvious seasonal variations, with CO 2 concentrations showing high in winter and low in summer and CH 4 showing a distinct "W"-shaped trend while N 2 O and SF 6 showing little difference between the four seasons. A relatively strong correlation and homology exist among the four greenhouse gases except in summer, and the analysis based on backward trajectories model shows that the Akedala Station is in uenced by the air ow from northwest or southwest throughout the year. The Akedala station is an important atmospheric background station in Central Asia, and its greenhouse gas concentration levels and variation characteristics are signi cantly different from those of the background stations in the monsoon region. It's degree changes are closely related to local source emissions, monsoon transport, and atmospheric photochemical processes.