Hydrogen Fluoride Total Column Research Articles

Ground-based measurements of HF and HCl total columns in atmosphere near Saint Petersburg (2009–2023)

ABSTRACT Monitoring of the ozonosphere requires observing the concentration of gases involved in the formation and depletion processes of stratospheric ozone. This study focuses on optimization the ground-based Fourier transform infrared (FTIR) method of retrieving total columns of halogen-containing gases hydrogen chloride (HCl) and hydrogen fluoride (HF). The work describes generally the procedure for selecting parameters to update the technique for deriving their atmospheric contents. Using parameters of the optimized methods, we obtained temporal variability of daily mean values of HCl and HF total columns above St. Petersburg from March 2009 to March 2023 by ground-based measurements of direct solar radiation spectra with a Bruker IFS 125 HR (IR Fourier spectrometer). The linear trends amount to (0.59 ± 0.27) %/year and (−0.26 ± 0.21) %/year for HF and HCl, respectively. The seasonal variability of both gases content was also calculated. The peak of HF total column occurred in March, while the low was observed in November. April showed the maximum of HCl content annually, and the lowest HCl total column appeared in the mid-winter. The results were compared with datasets from the nearest NDACC sites Harestua and Kiruna. Trends and seasonal cycles at the sites are consistent. The analysis of the variability of HCl to HF contents ratio demonstrated the time periods of decrease in HCl content caused by the chemical activity in the stratosphere. Finally, we analysed the ozone layer state over St. Petersburg at the beginning of 2023 using ground-based FTIR-measurements of HCl and HF total columns and satellite measurements of ozone total columns.

Ground-based measurements of HF total column abundances in the stratosphere near St. Petersburg (2009–2013)

An analysis of ground-based spectroscopic measurements of hydrogen fluoride total column abundances (HF TCAs) near St. Petersburg for a 4-year period (2009–2013) is performed. The average HF TCA is 1.93 × 1015 cm−2, and the RMS variation (natural variability) for the measurement ensemble is about 20%. The data are in good agreement with measurements collected at the NDACC stations (Bremen and Harestua), taking into account the differences in latitude. The monthly average HF TCAs show seasonal variation with peaks in late winter and early spring and troughs in the period from November to January. The variability of the monthly averages is at a maximum in winter and spring. A comparison of the HF TCAs from ground-based measurements with those from ACE-FTS solar occultation measurements shows that the total abundances from the ground-based data are 12% lower than those from the ACE-FTS data, and the RMS differences depend on the version of the satellite data processing system, being 13 and 16% for versions 2.2 and 3.0, respectively. The calculated ratio between HCl and HF total column abundances is significantly lower in late winter and spring. The linear trend of this ratio is 2.5% per year. Although the trend statistics is insufficient due to the short observation period, the pattern is explained both by the decrease in the stratospheric HCl content and the small increase in HF TCAs over the studied period and is consistent with literature data.

Derivation of tropospheric methane from TCCON CH<sub>4</sub> and HF total column observations

Abstract. The Total Carbon Column Observing Network (TCCON) is a global ground-based network of Fourier transform spectrometers that produce precise measurements of column-averaged dry-air mole fractions of atmospheric methane (CH4). Temporal variability in the total column of CH4 due to stratospheric dynamics obscures fluctuations and trends driven by tropospheric transport and local surface fluxes that are critical for understanding CH4 sources and sinks. We reduce the contribution of stratospheric variability from the total column average by subtracting an estimate of the stratospheric CH4 derived from simultaneous measurements of hydrogen fluoride (HF). HF provides a proxy for stratospheric CH4 because it is strongly correlated to CH4 in the stratosphere, has an accurately known tropospheric abundance (of zero), and is measured at most TCCON stations. The stratospheric partial column of CH4 is calculated as a function of the zonal and annual trends in the relationship between CH4 and HF in the stratosphere, which we determine from ACE-FTS satellite data. We also explicitly take into account the CH4 column averaging kernel to estimate the contribution of stratospheric CH4 to the total column. The resulting tropospheric CH4 columns are consistent with in situ aircraft measurements and augment existing observations in the troposphere.

Observed and simulated time evolution of HCl, ClONO<sub>2</sub>, and HF total column abundances

Abstract. Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO2, the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO2, and HF are calculated from both measurement and model time series data, with a focus on the time range 2000–2009. This period is chosen because from most of the measurement sites taking part in this study, data are available during these years. The precision of the trends is estimated with the bootstrap resampling method. The sensitivity of the trend results with respect to the fitting function, the time of year chosen and time series length is investigated, as well as a bias due to the irregular sampling of the measurements. The measurements and model results investigated here agree qualitatively on a decrease of the chlorine species by around 1% yr−1. The models simulate an increase of HF of around 1% yr−1. This also agrees well with most of the measurements, but some of the FTIR series in the Northern Hemisphere show a stabilisation or even a decrease in the last few years. In general, for all three gases, the measured trends vary more strongly with latitude and hemisphere than the modelled trends. Relative to the FTIR measurements, the models tend to underestimate the decreasing chlorine trends and to overestimate the fluorine increase in the Northern Hemisphere. At most sites, the models simulate a stronger decrease of ClONO2 than of HCl. In the FTIR measurements, this difference between the trends of HCl and ClONO2 depends strongly on latitude, especially in the Northern Hemisphere.

Trends of HCl, ClONO<sub>2</sub>, and HF column abundances from ground-based FTIR measurements in Kiruna (Sweden) in comparison with KASIMA model calculations

Abstract. Trends of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) total column abundances above Kiruna (Northern Sweden, 67.84° N, 20.41° E) derived from nearly 14 years (1996–2009) of measurement and model data are presented. The measurements have been performed with a Bruker 120 HR (later Bruker 125 HR) Fourier transform infrared (FTIR) spectrometer and the chemistry-transport model (CTM) used was KASIMA (KArlsruhe SImulation model of the Middle Atmosphere). The total column abundances of ClONO2 and HF calculated by KASIMA agree quite well with the FTIR measurements while KASIMA tends to underestimate the HCl columns. To calculate the long-term trends, a linear function combined with an annual cycle was fitted to the data using a least squares method. The precision of the resulting trends was estimated with the bootstrap resampling method. For HF, both model and measurements show a positive trend that seems to decrease in the last few years. This suggests a stabilisation of the HF total column abundance. Between 1996 and 2009, KASIMA simulates an increase of (+1.51±0.07) %/yr which exceeds the FTIR result of (+0.65±0.25) %/yr. The trends determined for HCl and ClONO2 are significantly negative over the time period considered here. This is expected because the emission of their precursors (chlorofluorocarbons and hydrochlorofluorocarbons) has been restricted in the Montreal Protocol in 1987 and its amendments and adjustments. The trend for ClONO2 from the FTIR measurements amounts to (−3.28±0.56) %/yr and the one for HCl to (−0.81±0.23) %/yr. KASIMA simulates a weaker decrease: For ClONO2, the result is (−0.90±0.10) %/yr and for HCl (−0.17±0.06) %/yr. Part of the difference between measurement and model data can be explained by sampling and the stronger annual cycle indicated by the measurements. There is a factor of about four between the trends of HCl and ClONO2 above Kiruna for both measurement and model data.