PNNL

Abstract

In the recent article by Byrne and Goldblatt, “Radiative forcing for 28 potential Archean greenhouse gases,” Clim. Past. 10, 1779-1801 (2014), the authors employ the HITRAN2012 spectroscopic database to evaluate the radiative forcing of 28 Archean gases. As part of the evaluation of the status of the spectroscopy of these gases in the selected spectral region (50-1800 cm-1), the cross sections generated from the HITRAN line-by-line parameters were compared with those of thethe ones provided in the PNNL database of experimental cross sections recorded at moderate resolution. The authors claimed that for NO2, HNO3, H2CO, H2O2, HCOOH, C2H4, CH3OH and CH3Br there are large or sometimes severe disagreements between the databases. In this work we show that for only for three of these gases does a modest discrepancy exist between the two databasesthe disagreements observed by the authors exist and we explain their origin of the differences. For the other five gases the disagreements are not nearly at the scale suggested by the authors, while we explain some of the differences that do exist. In summary, the agreement between the HITRAN and PNNL databases is very good, although not perfect. Typically differences are on the order of 1 to 10% (VERIFY), provided that HITRAN data exist for the bands/wavelengths of interest. It appears that a molecule-dependent combination of errors have affected the conclusions of the authors. In aAt least in one case it appears that they did not take the correct file from PNNL (NO2 + NO2 dimer was used in place of the monomer). Finally, cross sections of HO2 from HITRAN (which do not have a PNNL counterpart) are not calculated correctly