Information content of ground-based FTIR method for atmospheric HNO3 vertical structure retrieval
Ya.A. Virolainen, Yu.M. Timofeyev, A.V. Poberovsky, A.V. Polyakov
Saint Petersburg State University, St. Petersburg, Russia
Keywords: atmospheric nitric acid, information content and accuracy of measurements, vertical resolution, FTIR ground-based measurements
Abstract
Nitric acid plays an important role in atmospheric chemistry; therefore, it is currently monitored by various methods and instruments. Ground-based FTIR method based on spectral measurements of solar radiation by Bruker Optics IFS 125HR spectrometers allows to retrieve not only the total column HNO3, but also its content in several atmospheric layers. We analyze time series of HNO3 measurements at St. Petersburg NDACC site between 2009 and 2021. We demonstrate that FTIR measurements can provide information on HNO3 content in at least two atmospheric layers; the degrees of freedom for signal in average totals 3.1. The mean random error of HNO3 measurements amount to 3.9, 14 and 1.6% for total atmospheric, tropospheric (up to 15 km), and stratospheric (above 15 km) content, respectively. Thus, the FTIR-method considered is more sensitive to changes in the stratospheric HNO3 content. The absorption of solar radiation by nitric acid in the measured spectra overlaps with the absorption by water vapor; therefore, the information content and accuracy of HNO3 measurements are maximal in winter and minimal in summer: in winter, measurements are carried out mainly at low sun and low humidity, and in summer, vice versa.
|
