IMPROVED SPECTROSCOPIC DATA FOR NITRIC ACID AND FIRST OBSERVATION OF ATMOSPHERIC H{sup}15NO{sub}3 IN MIPAS SPECTRA: RETRIEVAL STUDY FOR THE H{sup}15NO{sub}3/H{sup}14NO{sub}3 ISOTOPIC RATIO

摘要

An improved set of spectral line parameters for nitric acid has recently been generated for both the H{sup}14NO{sub}3 and the H{sup}15NO{sub}3 isotopologues in the frequency range covered by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the ENVISAT satellite. These spectral parameters, now included in the last version of the MIPAS-dedicated spectroscopic database, have demonstrated to provide more accurate simulations of MIPAS atmospheric limb-emission spectra. In particular, a better consistency with the observations has been achieved in correspondence of the spectral features of the H{sup}14NO{sub}3 isotopologue. The spectral parameters of the 15{sup left}N isotopologue of nitric acid (relative to the fundamental ν{sub}5 band) led to the identification in MIPAS spectra of its Q-branch, thus allowing us to detect for the first time the H{sup}15NO{sub}3 molecule in the atmosphere. The successful identification of the H{sup}15NO{sub}3 features pushed us to investigate the possibility to retrieve vertical distribution profiles of the H{sup}15NO{sub}3/H{sup}14NO{sub}3 isotopic ratio. For this purpose we have implemented a dedicated retrieval approach based on the existing two-dimensional inversion system developed at Bologna University. In this work we show the preliminary results of simulated retrievals of the H{sup}15NO{sub}3/H{sup}14NO{sub}3 isotopic ratio.