Understanding the variations and sources of CO, C2H2, C2H6, H2CO and HCN columns based on three years of new ground-based FTIR measurements at Xianghe, China.

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 globally, affecting air quality and climate change. However, the variations and correlations among these species are not well known in North China, due to limited measurements. In June 2018, we installed a new ground-based Fourier-transform infrared (FTIR) spectrometer (Bruker IFS 125HR) recording mid-infrared high spectral resolution solar-absorption spectra at Xianghe (39.75° N, 116.96° E), China. In this study, we use the latest SFIT4 code, together with advanced a priori profile and spectroscopy, to retrieve these five species from the FTIR spectra measured between June 2018 and November 2021. The retrieval strategies, retrieval information, and retrieval uncertainties are presented and discussed. For the first time, the time series, variations, and correlations of these five species are analyzed at a typical polluted site 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, the FTIR measurements show that there is almost no seasonal variation in the CO column. The correlation coefficients (R) between the synoptic variations of CO and the other four species (C₂H₂, C₂H₆, H₂CO, and HCN) are between 0.68 and 0.80, indicating that they are affected by common sources. Using the FLEXPART model backward simulations and satellite fire measurements, we find that the variations of CO, C₂H₂, C₂H₆, and H₂CO columns are mainly dominated by the local anthropogenic emissions, while HCN column observed at Xianghe is a good tracer to identify fire emissions. [ABSTRACT FROM AUTHOR]