Variations and correlations of CO, C₂H₂, C₂H₆, H₂CO and HCN columns derived from three years of ground-based FTIR measurements at Xianghe, China

Abstract. Carbon monoxide (CO), acetylene (C₂H₂), ethane (C₂H₆), formaldehyde (H₂CO), and hydrogen cyanide (HCN) are important trace gases in the atmosphere. They are highly related to biomass burning, fossil fuel combustion, and biogenic emissions, affecting air quality and climate change. Mid-infrared high spectral resolution solar-absorption spectra are continuously recorded by a Fourier-transform infrared (FTIR) spectrometer (Bruker IFS 125HR) at Xianghe (39.75° N, 116.96° E), China. In this study, we use the SFIT4 code to retrieve these five species from the FTIR spectra measured between June 2018 and November 2021. The retrieval strategies, retrieval information, and uncertainties are presented and discussed. For the first time, the time series, variations, and correlations of these five species are analyzed in North China. The seasonal variations of C₂H₂ and C₂H₆ total columns show a maximum in winter-spring and a minimum in autumn, whereas the seasonal variations of H₂CO and HCN show a maximum in summer and a minimum in winter. Unlike the other four species, there is almost no seasonal variation of the CO total column. Using the monthly means as the background, the synoptic variations of these species are investigated as well. The FTIR measurements at Xianghe reveal high correlations among these species, indicating that they are affected by common sources. The correlation coefficients (R) between CO and the other four species (C₂H₂, C₂H₆, H₂CO, and HCN) are between 0.68 and 0.80. The FLEXible PARTicle dispersion model (FLEXPART) v10.4 backward simulations are used to understand the airmass sources observed at Xianghe, and it is found that the high column abundances are coming mainly from local anthropogenic emissions. Using satellite measurements, we show that the boreal forest fire emissions in Russia can lead to enhanced HCN total columns at Xianghe.