Detection of Temporal and Spatial Distributions of Atmospheric Nitric Acid Based on Ground-Based High-Resolution Solar Absorption Spectra

© 2020, Chinese Lasers Press. All right reserved. In this study, the high-resolution Fourier transform infrared spectroscopy (FTIR) is used to detect the concentrations of nitric acid (HNO3) in the atmosphere above the Hefei site. The vertical profiles and total columns of HNO3 are retrieved from the mid-infrared solar absorption spectra using the optimal estimation method. The vertical profiles and time series of the total columns of atmospheric HNO3 are obtained over the entire year of 2017. Further, the characteristics of the seasonal variation of HNO3, sensitivity altitude of concentration detection, averaging kernels of retrieved profiles, and degrees of freedom are analyzed. The vertical profiles of atmospheric HNO3 in different seasons denote that the HNO3 concentrations are higher at an altitude of 2030 km in the stratosphere and that they are lower in the troposphere. Furthermore, the total columns of HNO3 exhibit obvious seasonal variations, with a maximum in spring and minimum in winter. The amplitude of the seasonal variations is 9.82×1015 molecule/cm2. The data products obtained from the Aura MLS satellite are selected for performing comparison with the ground-based data to validate the measurements of the ground-based FTIR using independent data. The comparison results denote that the ground-based remote sensing and satellite observations display a consistent seasonal HNO3 variability. The ground-based data exhibits a good agreement with the satellite data with a high correlation coefficient of 0.83 even though the partial columns of the satellite data are lower than the corresponding ground-based total columns. The observation results indicate the reliability and accuracy of the ground-based FTIR for observing the temporal and spatial distributions of the atmospheric HNO3