Abstract
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 (THF) and column-averaged dry-air mole fractions of HF (XHF). 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 (1σ)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the XHF 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 XHF time series from 2015 to 2020 showed a negative trend of (−0.38 ± 0.22) % per year. The variability of XHF 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.
Highlights
MIR hydrogen fluoride (HF) measurements over Hefei to understand the discrepancies between these two datasets better and to know whether these two datasets can be combined to form more reliable data for evaluation, seasonal cycles, and long-term trend analyses
All NIR daily mean time series from 2015 to 2020 were mapped into the MIR retrieval scenarios following the procedures in Section 2.5 and compared with the concurrent MIR data
In this part of the study, we investigate the potential factors that drive the observed seasonality of HF, which shows the maximum concentration in the late winter to spring and minimum concentration in later summer to autumn
Summary
As a long-lived and chemical stable species in the stratosphere, hydrogen fluoride (HF) is a dominant reservoir of stratospheric fluorine species [1,2]. HF has a stratospheric lifetime on the order of more than 10 years [3]. Stratospheric HF is mainly produced from the photolysis of anthropogenic chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) [4,5]. Stratospheric HF is removed by either transport downward to the troposphere and wet deposited along with rainfall or transport upward to the Remote Sens. Total systematic error Total error DOFS (-)
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