Some improvements of the HNO₃ spectroscopic parameters in the spectral region from 600 to 950 cm^-1

In an earlier study [Flaud JM, Brizzi G, Carlotti M, Perrin A, Ridolfi M. MIPAS database: validation of HNO₃ line parameters using MIPAS satellite measurements. Atmos Chem Phys 2006;6:1-12] the HNO₃ line parameters in the HITRAN spectroscopic database have recently been revisited in the interval corresponding to the MIPAS spectral range. For the 11.3 μm region these updates involve the line positions for the {ν₅, 2ν₉} bands, and the intensities. However, comparisons between observed spectra recorded by MIPAS and the calculated ones in the 600-950 cm^-1 region still show significant disagreements. The goal of the present paper is to solve some of these problems. Based on the analysis of N₂-broadened HNO₃ laboratory spectra recorded with a Fourier transform instrument, a new HNO₃ database was generated, including the following improvements: (i) approximate parameters for the ν₅+ν₇-ν₇ and ν₅+ν₆-ν₆ hot bands have been added, and (ii) the intensities for the ν₆ and ν₈ bands have been updated. (iii) The air broadening and its temperature dependence, calculated using a semi-classical approach, have been added for each HNO₃ transition. (iv) Finally, line-mixing effects have been pointed out, particularly in the ν₅+ν₉-ν₉ Q branch, and an approach correctly modeling the resulting spectral shape is proposed.