ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-6-1913-2006 Aerosol light absorption in the North Atlantic: trends and seasonal characteristics during the period 1989 to 2003 Junker C. 1 2 Jennings S. G. 2 Cachier H. 3 Laboratoire d’Aérologie (URA CNRS 354), Université Paul Sabatier, Toulouse, France Atmospheric Research Group, Department of Physics, National University, Galway, Ireland Laboratoire des Sciences du Climat et de l’Environnement, Laboratoire mixte CNRSCEA, av. de la Terrasse, 91198 Gif sur Yvette, France 02 06 2006 6 7 1913 1925 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.net/6/1913/2006/acp-6-1913-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/1913/2006/acp-6-1913-2006.pdf

Aerosol light attenuation on quartz fibre filters has been measured since February 1989 at the Mace Head Atmospheric Research station near Carna, Co. Galway, Ireland, using an Aethalometer. <P style="line-height: 20px;"> The frequency of occurrence of the hourly averaged aerosol absorption data is found to be bimodally distributed. The two modes result from clean marine air and anthropogenically polluted continental air both being advected to the station dependent on the prevailing wind direction. The hourly averages of the marine portion of the aerosol light absorption are found to follow closely a lognormal distribution with a geometric mean of 0.310&nbsp;Mm<sup>-1</sup>. The&nbsp;hourly averages of continental sector aerosol absorption are neither normally nor lognormally distributed and have an arithmetic mean of 6.36&nbsp;Mm<sup>-1</sup>, indicating the presence of anthropogenic sources for BC east of the Mace Head station. <P style="line-height: 20px;"> The time series of the monthly averaged attenuation coefficient &sigma;<sub>att</sub> of both marine and continental sector aerosol shows an increase from 1989 to 1997 and a levelling off thereafter. <P style="line-height: 20px;"> The monthly maximum of marine sector &sigma;<sub>att</sub> is found in May. Trend and seasonal characteristics of the clean marine aerosol attenuation coefficients observed at Mace Head appear to be driven by meteorological factors, as indicated by rainfall data and by trends in&nbsp;the North Atlantic Oscillation (NAO) indices. The observed increasing trends of the continental sector &sigma;<sub>att</sub> from 1989 up to 1997 are possibly related to changes in BC emissions over Ireland, calculated from UNSTAT (2002) fuel consumption data.