Monitoring the atmospheric CO2 columns inside and around a city is of great importance to understand the temporal–spatial variation of XCO2 near strong anthropogenic emissions. In this study, we use two FTIR CO2 column measurements in Beijing (Bruker EM27/SUN) and Xianghe (Bruker IFS 125HR) between 2019 and 2021 to investigate the differences of XCO2 between Beijing (urban) and Xianghe (suburb) in North China and to validate the OCO-2 and OCO-3 satellite XCO2 retrievals. The mean and standard deviation (std) of the ΔXCO2 between Beijing and Xianghe (Beijing–Xianghe) observed by two FTIR instruments are 0.206 ± 1.736 ppm, which has a seasonal variation and varies with meteorological conditions (wind speed and wind direction). The mean and std of the XCO2 differences between co-located satellite and FTIR measurements are −0.216 ± 1.578 ppm in Beijing and −0.343 ± 1.438 ppm in Xianghe for OCO-2 and 0.637 ± 1.594 ppm in Beijing and 1.206 ± 1.420 ppm in Xianghe for OCO-3. It is found that the OCO-3 snapshot area mode (SAM) measurements can capture the spatial gradient of XCO2 between urban and suburbs well. However, the FTIR measurements indicate that the OCO-3 SAM measurements are about 0.9–1.4 ppm overestimated in Beijing and Xianghe.

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.

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