Remote Sensing of Atmospheric Hydrogen Fluoride (HF) over Hefei, China with Ground-Based High-Resolution Fourier Transform Infrared (FTIR) Spectrometry

Remote sensing of atmospheric hydrogen fluoride (HF) is challenging because it has weak absorption signatures in the atmosphere and is surrounded by strong absorption lines from interfering gases. In this study, we first present a multi-year time series of HF total columns over Hefei, China by using high-resolution ground-based Fourier transform infrared (FTIR) spectrometry. Both near-infrared (NIR) and mid-infrared (MIR) solar spectra suites, which are recorded following the requirements of Total Carbon Column Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC), respectively, are used to retrieve total column of HF (T-HF) and column-averaged dry-air mole fractions of HF (X-HF). The NIR and MIR observations are generally in good agreement with a correlation coefficient (R) of 0.87, but the NIR observations are found to be (6.90 +/- 1.07 (1 sigma)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the X-HF over Hefei showed a maximum monthly mean value of (64.05 +/- 3.93) pptv in March and a minimum monthly mean value of (45.15 +/- 2.93) pptv in September. The observed X-HF time series from 2015 to 2020 showed a negative trend of (-0.38 +/- 0.22) % per year. The variability of X-HF is inversely correlated with the tropopause height, indicating that the variability of tropopause height is a key factor that drives the seasonal cycle of HF in the stratosphere. This study can enhance the understanding of ground-based high-resolution remote sensing techniques for atmospheric HF and its evolution in the stratosphere and contribute to forming new reliable remote sensing data for research on climate change.