These measurements are often used to identify polar intrusion events and monitor chlorine species during the ozone hole period. Rinsland (1991) obtained a long-term time series of atmospheric HNO 3 total columns at mid-latitudes using ground-based FTIR, and compared the data with the values reported in other studies for mid-latitude. Total column and vertical profiles of HNO 3 and HCl were obtained by ground-based FTIR over the past decade. FTIR measurements are often used to analyze the long-term trends, seasonal variabilities of trace gases and to validate in-situ and satellite measurements. The ground-based FTIR technique detects the long-term trend of trace gases in the atmosphere with high precision and accuracy, and the measurements are not affected by vertical air-mass transport.

However, satellite data show high measurement error and low sensitivity for near-surface observations. The global temporal and spatial distributions of HNO 3 and HCl can be obtained by satellite remote sensing instruments, such as the Infrared Atmospheric Sounding Interferometer (IASI on MetOp satellite), the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS on SCISAT), the Microwave Limb Sounder (MLS carried on Aura), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Airborne or balloon-borne in-situ measurements with high accuracy and precision have been performed to detect HNO 3 and HCl concentrations and vertical profiles, but the measurements are easily affected by vertical airmass transport. HNO 3 and HCl have been measured by many methods and techniques. The mean bias between satellite and FTIR data of stratospheric HNO 3 and HCl columns are (−8.58 ± 12.22)% and (4.58 ± 13.09)%, respectively. MLS satellite data showed similar seasonal variations and annual rates with FTIR data, and the stratospheric HNO 3 and HCl columns of the two datasets have correlation coefficients (r) of 0.87 and 0.88, respectively. Further, HNO 3 and HCl data were used to compare with Microwave Limb Sounder (MLS) satellite data. The seasonal amplitudes of stratospheric HNO 3 and HCl are 2.67 × 10 15 molec cm −2 and 4.76 × 10 14 molec cm −2 respectively, both reaching their maximum in March and their minimum in September, due to the tropopause height variation. The time series of stratospheric HNO 3 and HCl columns from January 2017 to December 2019 showed similar annual variation trends, with an annually decreasing rate of (−9.45 ± 1.20)% yr −1 and (−7.04 ± 0.81)% yr −1 for stratospheric HNO 3 and HCl, respectively. Vertical profiles and stratospheric HNO 3 and HCl columns are retrieved by ground-based high resolution Fourier transform infrared spectroscopy (FTIR) remote sensing measurements at the Hefei site in China.

Hno3 vapour absorption