Observations of CH4, CH3D and H2CO at Ile de La Réunion from ground-based FTIR and MAXDOAS campaign measurements

Abstract

Ile de La Réunion (21°S, 55°E) is candidate to become a primary station the ground-based Network for the Detection of Atmospheric Composition Change (NDACC) which was formed to provide long-term monitoring of atmospheric trace gases at globally distributed sites. Ground-based network data are also very valuable for the validation of satellite data, such as SCIAMACHY, ACE-FTS and IASI. Up to now, only a few NDACC stations are located in the Southern Hemisphere, and none of them is at subtropical latitude. Three campaigns of FTIR measurements were made at the Ile de La Réunion in preparation of a near future permanent installation, namely in October 2002, from August to October 2004, and from May to November 2007. A UV-visible Multi-Axis DOAS (MAXDOAS) instrument was operated at the same site from July 2004 to June 2005. The inversion algorithms for both the MAXDOAS and FTIR spectral data analyses use the Optimal Estimation Method to derive information about the vertical distribution of the target gases. We will present the vertical profiles and total columns of the greenhouse gas CH4 and its isotopologue CH3D, obtained from the FTIR measurements. For the latter, the number of degrees of freedom for signal is close to one, limiting the information to the total column abundance. Early comparisons with correlative measurements from satellite data will be discussed. Formaldehyde (H2CO) is a source of HOx and an indicator for biogenic emissions, biomass burning, and anthropogenic pollution. It can be measured by both the FTIR and UV-Visible MAXDOAS instruments. The total columns obtained by the two techniques in the common period of measurements August-October 2004 will be discussed. We will also show the comparisons of the time series for formaldehyde from both instruments with correlative SCIAMACHY data above La Réunion