Retrieval of Tropospheric BrO and NO2 from UV-Visible Observations

This contribution has been concerned with three different activities. First, global N0₂ data records from HALOE, POAM-II and POAM-III satellite instruments complemented by ground-based data sets from the NDSC, have been investigated for mutual consistency and exploited to build a global time-latitude stratospheric NO₂ profile climatology that may be used for tropospheric NO2 retrieval from ERS2-G0ME. Second, a BrO total column product derived from GOME has been created over the total present lifetime of the ERS-2 satellite (1996 to 2002) and made available to the scientific community through a dedicated web site. In addition, a prototype improved GOME BrO retrieval algorithm has been designed with the aim to determine better global tropospheric BrO columns from the combined use of GOME data and three-dimensional model data, and to provide the stratospheric reference needed in a tropospheric residual approach. Third, ground-based multi-axis DOAS measurements have been conducted at the Observatoire de Haute Provence, (OHP, 44 °N) between January 2001 and June 2002 in support of satellite retrieval activities. Results obtained demonstrate the high sensitivity of the measurements to tropospheric amounts of NO₂ and HCHO, as well as the potential of the technique to unravel small mid-latitude free-tropospheric BrO contents. As to the latter point, comparisons between combined GOME-SLIMCAT and MAX-DOAS tropospheric BrO evaluations suggest that approximately half of the mid-latitude BrO total column resides in the troposphere.