ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-17913-2011 Interpreting elevated space-borne HCHO columns over the Mediterranean Sea using the OMI and SCIAMACHY sensors Sabolis A. 1 Meskhidze N. 1 Curci G. 2 Palmer P. I. 3 Gantt B. 1 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA CETEMPS – Department of Physics, University of L'Aquila, Italy School of GeoSciences, University of Edinburgh, Edinburgh, UK 24 06 2011 11 6 17913 17940 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/11/17913/2011/acpd-11-17913-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/17913/2011/acpd-11-17913-2011.pdf

Formaldehyde (HCHO) is an oxidation product of a wide range of volatile organic compounds (VOCs) and important atmospheric constituent found in both the polluted urban atmosphere and remote background sites. In this study, remotely sensed data of HCHO vertical column densities are analyzed over the Mediterranean Sea using the Ozone Monitoring Instrument (OMI). Data analysis indicates a marked seasonal cycle with a summer maximum and winter minimum confined to the marine environment during a three year period (2005–2007) examined. A possible retrieval artifact associated with Saharan dust transport over the region is explored by changing intensity of Saharan dust sources in GEOS-Chem following the recommendation of Generoso et al. (2008). Recalculated air mass factors (AMF), based on the new values of aerosol loadings, lead to a reduction of the summertime "hot spot" in OMI retrieval of HCHO columns over the Mediterranean Sea; however, even after the correction, enhanced values are still present in this region. To explain these values, marine biogenic sources of VOCs are examined. Calculations indicate that emissions of phytoplankton-produced isoprene and monoterpenes are not likely to explain the enhanced HCHO columns over the Mediterranean Sea. <br><br> To further understand spatial and seasonal variation of HCHO over the Mediterranean Sea, OMI HCHO columns are compared to those of the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) sensor. Unlike OMI retrievals, over the Mediterranean Sea SCIAMACHY HCHO columns did not reveal clear seasonality during the three years and the two sensors did not agree within their retrieval uncertainty. Overall, comparison of OMI and SCIAMACHY HCHO columns were inconclusive. Moreover, retrievals of HCHO columns over other water bodies showed that the two sensors agree reasonably well over the Equatorial Pacific region, Gulf of Mexico, and the North Sea, but do not show similar magnitudes or seasonal variations over oligotrophic water bodies such as Mediterranean Sea, Northwestern and Southern Pacific Oceans. Model simulations in conjunction with measurements studies may be required to fully explore the complex mechanism of HCHO formation over the Mediterranean and its implications for the air quality in the region.

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