J. Phys. Chem. A 2010, 114, 10045–10048
10045
New Laboratory Intercomparison of the Ozone Absorption Coefficients in the Mid-infrared (10 µm) and Ultraviolet (300-350 nm) Spectral Regions A. Gratien,† B. Picquet-Varrault,* J. Orphal,‡ J.-F. Doussin, and J.-M. Flaud Laboratoire InteruniVersitaire des Syste`mes Atmosphe´riques, UMR-CNRS 7583, UniVersite´ Paris-Est et UniVersite´ Paris Diderot, Institut Pierre Simon Laplace (IPSL), Cre´teil, France ReceiVed: May 2, 2010; ReVised Manuscript ReceiVed: August 16, 2010
Knowing the ozone absorption cross sections in the ultraviolet and infrared spectral range, with an accuracy of better than 1%, is of the utmost importance for atmospheric remote-sensing applications. For this reason, various ozone intensity intercomparisons and measurements have been published these last years. However, the corresponding results proved not to be consistent and thus have raised a controversial discussion in the community of atmospheric remote-sensing. This study, where great care has been taken to avoid any possible error, reports a new laboratory intercomparison of the ozone absorption coefficients in the mid-infrared (10 µm) and ultraviolet (300-350 nm) spectral regions. It gives a new piece of information to the puzzling problem concerning the ozone IR and UV cross sections and confirms that the IR and UV cross sections recommended in the literature are in disagreement of about 4%. 1. Introduction Ozone plays a key role in the atmosphere. For measuring atmospheric ozone concentrations, both mid-infrared and ultraviolet absorption techniques are used by ground-, air- or satellite-based instruments. In order to obtain accurate ozone concentrations as well as to compare in a meaningful way ozone concentrations measured in different spectral regions, the knowledge of the absorption cross sections, with an accuracy of better than 1%, is of the utmost importance. For these reasons, a study by Picquet-Varrault et al.,1 entitled “Laboratory Intercomparison of the Ozone Absorption Coefficients in the Midinfrared (10 µm) and Ultraviolet (300-350 nm) Spectral Regions” was been published in this journal more than 5 years ago; it was concerned with the consistency between the absorption cross sections of ozone in the Huggins bands (300-350 nm) and the mid-infrared region around 10 µm. This study was performed in our research group by simultaneously acquiring UV and IR spectra at room temperature and atmospheric pressure using a common optical cell. The intercomparison of UV and IR cross sections has revealed systematic differences of about 5.5% between the recommendation of HITRAN 20042 for the mid-infrared and the most referenced measurements in the UV region. At the same time, other intercomparisons between UV (or visible) and IR spectral range have been performed by other research groups. Between the Hartley and the 10 µm bands, seven intercomparison studies3-9 were published. These studies were always performed using the ozone absorption at the single wavelength of 254 nm in the peak of the Hartley band. Among these studies, three studies3-5 have shown a disagreement of about 4% between the absorption at 254 nm and the 10 µm bands, whereas four other studies6-9 have shown an agreement between these two spectral regions. One could then wonder * To whom correspondence should be addressed. Phone: +33 1 45 17 15 90; Fax: +33 1 45 17 15 64; E-mail: Benedicte.Picquet-Varrault@ lisa.u-pec.fr. † New address: Department of Chemistry, University of California, Irvine, USA. ‡ New address: IMK, Karlsruhe Institute of Technology (KIT), Germany.
whether these differences could not come from the UV cross sections used for the absorption of ozone at the single wavelength of 254 nm. However, for example the same UV reference10 used for the studies of Smith et al.4 and De BackerBarilly and Barbe6 are in disagreement. The intercomparison of G. Dufour et al.11 between the UV absorption at 253.7 nm and the infrared line intensity at 1052.143 cm-1 has shown that there is no systematic difference between the UV and IR (1-2%), whereas more recently the work of Ibrahim et al.12 shows a disagreement of about 5% between the Hartley (270-290 nm) and the 10 µm bands. The intercomparison of D. Dufour et al.13 concerning the 5 µm and 515-715 nm (Chappuis) spectral regions has shown an excellent agreement (
