Atmospheric Chemistry and Physics Discussions
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2005
10.5194/acpd-5-12815-2005
http://www.atmos-chem-phys-discuss.net/5/12815/2005/
http://www.atmos-chem-phys-discuss.net/5/12815/2005/acpd-5-12815-2005.html
http://www.atmos-chem-phys-discuss.net/5/12815/2005/acpd-5-12815-2005.pdf
12815
12855
2005-12-19
Aerosol light absorption in the North Atlantic: trends and seasonal characteristics during the period 1989 to 2003
C. Junker
junc@aero.obs-mip.fr
S. G. Jennings
H. Cachier
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 CNRS-CEA, av. de la Terrasse, 91198 Gif sur Yvette, France
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.
<br><br>
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 Mm<sup>−1</sup>. The hourly averages of continental sector aerosol
absorption are neither normally nor lognormally distributed and have an
arithmetic mean of 6.36 Mm<sup>−1</sup>, indicating the presence of
anthropogenic sources for BC east of the Mace Head station.
<br><br>
The time series of the monthly averaged attenuation coefficient σ<sub>att</sub> of
both marine and continental sector aerosol shows an increase from 1989 to
1997 and a levelling off thereafter. The monthly maximum of marine sector
σ<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 the North Atlantic Oscillation (NAO) indices.