Characteristics of atmospheric nitrous oxide observed at Mt. Waliguan GAW global station in the inland Eurasia during eighteen years

This study presents atmospheric N 2 O mole fractions measured from discrete air samples from 2001 to 2018 at Mt. Waliguan (WLG) station (36°17′N, 100°54′E, 3816 m asl) in China, which is a global background station of the World Meteorological Organization/Global Atmosphere Watch Programme (WMO/GAW) in central Eurasia. Observed N 2 O characteristics of annual means, interannual variability, and seasonal cycles were investigated. Our results show that N 2 O at WLG possess a distinct increasing trend and a statistically significant seasonal cycle, with an average growth rate of 0.9±0.01 ppb yr −1 (1σ)(1ppb=10 −9 ), which is close to the global mean. The detrended seasonal cycle shows a trough of −0.25±0.04 (1σ) ppb in June and a peak of 0.13±0.07 (1σ) ppb in September, with an amplitude of 0.38 ppb. The pattern is due to combined effects of variation in surface sources, vertical convection within the boundary layer and stratosphere to troposphere transportation (STE). The interannual variability in growth rate was partly driven by quasi-biennial oscillation (QBO) of tropical zonal wind through stratospheric transport into the troposphere. According to a cluster analysis of back trajectories and the corresponding average N 2 O load, most air masses cover arid and semi-arid areas in inner Asia with low N 2 O emissions, indicating that the atmospheric N 2 O at the WLG represents the background N 2 O level in central Eurasia.