ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-4-7757-2004 A pseudo-Lagrangian model study of the size distribution properties over Scandinavia: transport from Aspvreten to Värriö Tunved P. 1 Korhonen H. 2 Ström J. 1 Hansson H.-C. 1 Lehtinen K. E. J. 3 Kulmala M. 3 Institute for Applied Environmental Research, Stockholm University, SE-106 91, Stockholm, Sweden Finnish Meteorological Institute, POB 503, FIN-00101 Helsinki, Finland Department of Physical Sciences, University of Helsinki, POB 64, FIN-00014 Helsinki, Finland 29 11 2004 4 6 7757 7794 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/4/7757/2004/acpd-4-7757-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/4/7757/2004/acpd-4-7757-2004.pdf

The evolution of the aerosol size distribution during transport between Aspvreten (58.8&deg; N, 17.4&deg; E) and V&#228;rri&#246; (67.46&deg; N, 29.35&deg; E) was studied using a pseudo-Lagrangian approach. Aerosol dynamic processes were studied and interpreted utilizing a state-of-the-art aerosol dynamic box model UHMA (University of Helsinki Multicomponent Aerosol model) complemented with OH, NO<sub>3</sub>, O<sub>3</sub> and terpene chemistry. In the model simulations, the growth and formation of aerosol particles was controlled by sulphuric acid, ammonia, water and an unidentified low volatile organic compound. This organic compound was assumed to be a product of terpene oxidation with a yield of 13% in the base case conditions. <br><br> Changes of aerosol size distribution properties during transport between the stations were examined in twelve clear sky cases. On average, the modelled number agreed fairly well with observations. Mass concentration was overestimated by 10%. <br><br> Apart from dilution, the only removal mechanism for aerosol mass is dry deposition. A series of sensitivity tests performed revealed that the absolute magnitude of dry deposition effects on the aerosol size distribution is slow overall. Furthermore, nucleation does not leave a significant contribution to aerosol number in the selected cases. The sensitivity of the modelled size distribution to concentration of precursor gases and oxidants is, however, obvious. In order to explain observed mass increase during transport we conclude that a yield of low volatile products from oxidation of terpenes of 10&ndash;15% is required to explain observed growth rates. Coagulation is acknowledged to be highly important in modelled cases.