Ground-based FTIR and MAX-DOAS observations of formaldehyde at Réunion Island and comparisons with satellite and model data

Abstract

The FTIR and MAX-DOAS daily mean total columns agree very well: no significant bias is observed and the standard deviation of the comparisons is only 8%. Both FTIR and MAX-DOAS HCHO total columns are in good agreement with SCIAMACHY values in the 2004-2005 period, with standard deviations of 21% and 31%, respectively. The same seasonal cycle is observed by the different instruments, with a minimum in austral winter and a maximum in FebruaryMarch.The FTIR and MAX-DOAS data are confronted with HCHO columns calculated by a global CTM, the IMAGES model. The model underestimates the HCHO columns by 23-29% in comparison with FTIR, and by 15% in comparison with DOAS. This bias might have multiple causes, including an underestimation of OH concentrations in the model (as indicated by a sensitivity study using prescribedCorrespondence to: C. Vigouroux (corinne.vigouroux@aeronomie.be) OH fields) and/or an underestimated contribution of largescale transport of HCHO precursors from Madagascar. The latter hypothesis is comforted by the large observed day-today variability of HCHO columns, and by the observation that the peak values of FTIR columns can often be associated with free tropospheric transport patterns from source regions over Madagascar to Réunion Island, according to simulations performed with the Lagrangian particle dispersion model FLEXPART.

An evaluation of IASI-NH<sub>3</sub> with ground-based Fourier transform infrared spectroscopy measurements

“…Observed NH 3 columns (Fig. 2, purple) are usually low due to the lack of major sources near the site, but increases are observed during the fire season (September-November) with possible fire plumes originating from Madagascar, as already observed in another study involving short-lived species (Vigouroux et al, 2009). Local NH 3 emissions include fertilizer applied for sugar cane production and local biomass burning.…”

“…At the available sites, in situ measurements are mostly performed with relatively poor temporal resolution due to the high costs of performing reliable NH 3 measurements with high temporal resolution. These measurements of NH 3 are also hampered by sampling artefacts caused by the reactivity of NH 3 and the evaporation of ammonium nitrate (Slanina et al, 2001;von Bobrutzki et al, 2010;Puchalski et al, 2011). As the lifetime of atmospheric NH 3 is rather short, on the order of hours to a few days, due to efficient deposition and fast conversion to particulate matter, the existing surface measurements are not sufficient to estimate global emissions without inducing large errors.…”

Retrieval of ammonia from ground-based FTIR solar spectra

“…The island is prone to some local biomass burning and wild fire events, which are known to emit ammonia. It is also very close to Madagascar, a region with frequent and intense biomass burning events, and it has been found, using backward trajectory, that the emissions in Madagascar can be transported to Réunion Island within 1 day (Vigouroux et al, 2009). The measurements used in this study are performed with a Bruker 120M spectrometer.…”

Five years of CO, HCN, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, CH<sub>3</sub>OH, HCOOH and H<sub>2</sub>CO total columns measured in the Canadian high Arctic

“…CH 3 OH and HCOOH have been measured in a limited number of ground-based FTIR studies (Paton-Walsh et al, 2005Rinsland et al, , 2009Zander et al, 2010;Paulot et al, 2011). The first FTIR data sets of H 2 CO were obtained in remote areas (Mahieu et al, 1997;Notholt et al, 1997a, b) and were then extended to urban areas (Hak et al, 2005) and the Southern Hemisphere (Jones et al, 2009;Vigouroux et al, 2009;Paton-Walsh et al, 2010).…”