Direct Observations of Atmospheric Transport and Stratosphere-Troposphere Exchange from High-Precision Carbon Dioxide and Carbon Monoxide Profile Measurements

The balloon-borne Aircore campaign was conducted in Inner Mongolia,China,on June 13 and 142018,which detected carbon dioxide(CO2)and carbon monoxide(CO)profiles from surface to 24 km,showing strong positive and negative correlations between 8 km and 10 km on 13 and 14 June,respectively.Backward trajectories,meteorological analyses,and CO2 horizontal distributions were combined to interpret this phenomenon.The results indicated that the source region experienced a stratospheric intrusion and exhibited a large horizontal CO2 gradient;namely,lower CO concentrations corresponded to higher CO2 concentrations and vice versa.The laminar structure with multiple origins resulted in the highly negative correlation between CO2 and CO in the upper troposphere on 14 June.The contribution of stratospheric air mass to the upper troposphere and that of tropospheric air mass to the lower stratosphere were 26.7%and24.3%,respectively,based on a mass balance approach.Another interesting phenomenon is that CO2 and CO concentrations increased substantially at approximately 8 km on 13 June.An analysis based on the backward trajectory implied that the air mass possibly came from anthropogenic sources.The slope of CO2/CO representing the anthropogenic sources was 87.3 ppm ppm-1.In addition,the CO2 profile showed that there was a large CO2 gradient of 4 ppm km-1 within the boundary layer on 13 June,and this gradient disappeared on 14 June.

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.

An improved GC-ECD method for measuring atmospheric N_2O

Gas chromatography equipped with an electron capture detector （GC-ECD） has been widely used for measuring atmospheric N2O,but nonlinear response and the influence of atmospheric CO2 have been recognized as defects for quantification.An original GCECD method using N 2 as carrier gas was improved by introducing a small flow rate of CO2 makeup gas into the ECD,which could well remedy the above defects.The N2O signal of the improved method was 4-fold higher than that of the original method and the relative standard deviation was reduced from 〉 1% to 0.31%.N2O concentrations with different CO2 concentrations （172.2×10-6-1722×10-6mol/mol） measured by the improved GC-ECD method were in line with the actual N2O concentrations.However,the N2O concentrations detected by the original method were largely biased with a variation range of-4.5%～7%.The N2O fluxes between an agricultural field and the atmosphere measured by the original method were greatly overestimated in comparison with those measured by the improved method.Good linear correlation （R2=0.9996） between the response of the improved ECD and N2O concentrations （93×10-9-1966×10-9mol/mol） indicated that atmospheric N2O could be accurately quantified via a single standard gas.Atmospheric N2O concentrations comparatively measured by the improved method and a high precision GC-ECD method were in good agreement.

Atmospheric sulfur hexafluoride in-situ measurements at the Shangdianzi regional background station in China

We present in-situ measurements of atmospheric sulfur hexafluoride（SF6） conducted by an automated gas chromatograph–electron capture detector system and a gas chromatography/mass spectrometry system at a regional background site, Shangdianzi,in China, from June 2009 to May 2011, using the System for Observation of Greenhouse gases in Europe and Asia and Advanced Global Atmospheric Gases Experiment（AGAGE）techniques. The mean background and polluted mixing ratios for SF6 during the study period were 7.22 × 10-12（mol/mol, hereinafter） and 8.66 × 10-12, respectively. The averaged SF6 background mixing ratios at Shangdianzi were consistent with those obtained at other AGAGE stations located at similar latitudes（Trinidad Head and Mace Head）, but larger than AGAGE stations in the Southern Hemisphere（Cape Grim and Cape Matatula）. SF6 background mixing ratios increased rapidly during our study period, with a positive growth rate at 0.30 × 10-12year-1. The peak to peak amplitude of the seasonal cycle for SF6 background conditions was 0.07 × 10-12, while the seasonal fluctuation of polluted conditions was 2.16 × 10-12. During the study period, peak values of SF6 mixing ratios occurred in autumn when local surface horizontal winds originated from W/WSW/SW/SWS/S sectors, while lower levels of SF6 mixing ratios appeared as winds originated from N/NNE/NE/ENE/E sectors.