Understanding the distribution of atmospheric water vapor (H₂O) is crucial for global warming studies and climate change mitigation. In this study, we retrieved the ground layer, tropospheric and total columns of H₂O using ground-based high-resolution Fourier transform infrared spectrometry (FTIR). The H₂O total columns are obtained from near-infrared (NIR) and mid-infrared (MIR) spectra, and the ground layer and tropospheric H₂O columns are retrieved from the MIR spectrum. The total columns of H₂O retrieved from NIR and MIR have a good consistency (R = 0.989). Additionally, the ground layer H₂O columns have a similar seasonal variation to total columns and tropospheric columns but have a higher seasonal amplitude. The ground layer H₂O columns are close to the total columns and tropospheric columns in winter; however, in summer, the average difference between the ground layer and total columns and the value between the ground layer and tropospheric columns are large. This is mostly due to temperature variation. The temperature has a linear response to H₂O, and the relationship between surface temperature and ln(XH₂O) values in the ground layer, the entire atmosphere and the troposphere show a significantly positive correlation, and the correlation coefficient R is 0.893, 0.882 and 0.683, respectively. Furthermore, we selected the HYSPLIT model to simulate the back trajectories of air parcels in the four seasons in Hefei and find that the air mass transport has a significant impact on the local H₂O change. These results demonstrate that ground-based high-resolution FTIR technology has high accuracy and precision in observing the vertical distribution and seasonal changes of H₂O in different atmospheres.

Under the control of the Montreal Protocol and its amendments, hydrofluorocarbons (HCFCs) are used as temporary substitutes for ozone-depleting substances, such as chlorofluorocarbons, and are regulated for consumption and production. China plans to phase out HCFCs by 2030, and HCFC-22 (CHClF₂) is currently the most abundant HCFC in the atmosphere. This study measures the vertical profiles and total columns of atmospheric HCFC-22 from January 2017 to December 2022, based on the mid-infrared solar spectra recorded by the ground-based high-resolution Fourier transform infrared (FTIR) spectrometer at the Hefei remote sensing station. The HCFC-22 total columns over Hefei increased from 2017–2018 and gradually decreased in 2018–2022, with an annual variation rate of 5.98% and −1.02% ± 0.02%, respectively. Compared with the ACE-FTS satellite independent dataset, the FTIR data indicate good consistency with the ACE-FTS data at a 5–25 km altitude, with an average relative difference of −4.38 ± 0.83% between the vertical profiles. HCFC-22 emissions in the Yangtze River Delta from 2017 to 2022 are estimated, derived from measured total columns combined with the Lagrangian transport model and the Bayesian inversion technique. In the Yangtze River Delta, HCFC-22 emissions were high in 2017, with a value of 33.3 ± 16.8 kt, and decreased from 2018 to 2022, with a minimum of 27.3 ± 13.6 kt in 2022 during the observations.

Studies of the impact of biomass burning and the emissions of trace gases from biomass burning, especially using long-term observations, are scarce in China. We utilize solar absorption spectra obtained via ground-based high-resolution Fourier transform infrared (FTIR) spectroscopy to retrieve the atmospheric total columns and vertical profiles of carbon monoxide (CO), formaldehyde (H₂CO), and hydrogen cyanide (HCN) in Hefei, China. Seasonal and interannual variability in the three gases from 2016 to 2022 are analyzed. Atmospheric CO shows significant seasonal variations, peaking during spring and winter, and declining during summer, with a seasonal amplitude of 8.07 × 10¹⁷ molecules cm⁻² and a seasonal variability of 29.35%. H₂CO and HCN have similar seasonal patterns to each other, with high concentrations in summer and low concentrations in winter. The seasonal amplitude of H₂CO and HCN are 1.89 × 10¹⁶ molecules cm⁻² and 2.32 × 10¹⁵ molecules cm⁻², respectively, with a seasonal variability of 133.07% and 34.69%, respectively. The means of the annual variation rate for CO, H₂CO, and HCN are (−2.67 ± 2.88)% yr⁻¹, (2.52 ± 12.48)% yr⁻¹ and (−3.48 ± 7.26)% yr⁻¹, respectively. To assess the influence of biomass burning on the variations in column concentrations of the three gases, the correlation between CO, H₂CO, and HCN was analyzed. The months during which the monthly correlation coefficient between CO and H₂CO with HCN exceeds 0.8, and the fire radiative power (FRP) observed by satellites is larger than its monthly average are regarded as a biomass-burning occurrence in Anhui province. Additionally, the enhancement ratios of ΔH₂CO/ΔCO and ΔHCN/ΔCO were calculated for the periods impacted by the biomass burning. Finally, backward trajectory cluster analysis and the potential source contribution function (PSCF) calculation identified the air mass transport pathways and the potential source areas at the Hefei site.

Since the Industrial Revolution, anthropogenic activities, primarily fossil fuel combustion, have driven a sharp increase in ${\mathrm{CO}}_2$ emissions, making them the principal driver of global climate change. Precise monitoring and quantification of ${\mathrm{CO}}_2$ emissions are essential for effective greenhouse gas mitigation. Traditional “bottom-up” inventories often suffer from limited timeliness, low spatial resolution, and significant uncertainties. Satellite remote sensing offers an alternative “top-down” approach for emission estimation. Compared to existing ${\mathrm{CO}}_2$ sensors, ${\mathrm{NO}}_2$ observation satellites provide higher spatiotemporal resolution. Given that ${\mathrm{NO}}_2$ and ${\mathrm{CO}}_2$ are co-emitted during combustion with a stable relationship, ${\mathrm{NO}}_2$ can serve as an effective proxy to indirectly derive ${\mathrm{CO}}_2$ emissions. In this study, an exploratory framework for city-scale ${\mathrm{CO}}_2$ estimation was developed using TROPOMI ${\mathrm{NO}}_2$ column concentrations, MERRA-2 wind fields, EDGAR inventory and the ODIAC inventory. The analysis focused on seven major cities in Shandong Province, China, from April to September 2022. By integrating a wind-rotation technique with a line density model and the differential evolution (DE) algorithm, we derived ${\mathrm{NO}}_2$ emissions and atmospheric lifetimes. The ${\mathrm{NO}}_2{\mathrm{-to-CO}}_2$ relationship was established based on sector-weighted inventory data to quantify fossil-fuel ${\mathrm{CO}}_2$ fluxes. The results identify Qingdao, Jinan, and Linyi as emission hotspots, followed by Rizhao, with lower emissions observed in Yantai, Liaocheng, and Jining. Comparison with the ODIAC inventory illustrates that this framework provides a top-down constraint for identifying localized emission characteristics and potential discrepancies in bottom-up datasets. This study offers a complementary tool for near-real-time urban carbon monitoring during the non-heating season.

Sulfur hexafluoride (SF₆) is a typical long-lived greenhouse gas that has attracted considerable attention due to its extremely long atmospheric lifetime and high global warming potential. In this study, atmospheric SF₆ column concentrations from 2023 to 2025 were retrieved using ground-based high-resolution Fourier transform infrared (FTIR) remote sensing observations at the Hefei site, China. The seasonal variation and annual trends of SF₆ were analyzed, and the potential influencing regions and transport characteristics of high-value events were investigated by combining wind direction statistics with backward trajectory clustering analysis. The results show that high SF₆ column concentrations over Hefei mainly occurred in summer, while relatively low concentrations appeared in winter during the observation period from 2023 to 2025. The average total column concentration of SF₆ is 2.80 × 10¹⁴ molec·cm⁻², the average dry-air column-averaged mole fraction is 13.06 ppt, and the annual growth rate is 0.88 ppt yr⁻¹. The high-value events of SF₆ at the Hefei site are mainly concentrated in summer, and the wind direction mainly corresponds to the northeast and the southeast wind. The air masses with high concentrations of SF₆ mainly originated from the transportation path in the nearby southern regions of the station. During summer, the season with relatively higher SF₆ concentrations, the air masses were mainly southerly and easterly winds. The results of this study provide observational evidence and scientific support for understanding the characteristics of variation in atmospheric SF₆ column concentrations over Hefei and the influence of regional transport on high SF₆ values.