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Particle formation events were analysed from aerosol number size distribution data collected at a background station in southern Sweden between February 2001 and May 2004. Events occurred on about 36% of all days and were favoured by high global radiation values. The clearest events (class I, 20% of all days) were observed when the formation rate of activated hypothetical clusters around 1 nm diameter, J1 was higher than 10(180*CondS-0.60), where CondS is the condensation sink (in s-1). The median condensable vapour concentration, observed formation rate at 3 nm, and growth rate during class I events were 3.0 × 107 cm-3, 1.1 cm-3 s-1 and 2.1 nm h-1, respectively. On 7% of all days, it was possible to observe growth of the newly formed particles exceeding 30 nm geometric mean diameter during event days in the evening, which is important for the regional particle population, and thereby the climate. A trajectory analysis revealed that cleaner air masses were relatively more important for the contribution of Aitken mode particles than polluted ones. Class I events were registered on 36% of all days when trajectories had passed over the open sea, indicating that ship traffic can contribute to particle formation and growth.DOI: 10.1111/j.1600-0889.2008.00345.x

We use a recently developed parametrization to estimate the regional particle field in the summer time troposphere over Scandinavia that would result if the forest were the only source of particles. The calculated field is compared with available observational data. It is concluded that the needle leaf forest above 58°N alone is capable of producing aerosol mass concentrations corresponding to 12–50% of today's values in the boundary layer over Scandinavia. We also demonstrate that the forest itself could produce up to 200 CCN per cubic centimetre on average over Scandinavia and further show that an increase in temperature by 5.8 °C compared to today's average temperature could increase this CCN population by 40%. The study shows that we are able to approximate the natural aerosol field resulting from biogenic emissions over the boreal forest in the northern hemispheric region. This information provide an important contribution in the evaluation of the climate effect caused by anthropogenic emissions of particles over the forest and also opens the possibility to better address the climate feedbacks believed to be associated with the boreal region. DOI: 10.1111/j.1600-0889.2008.00363.x

Nearly 3 yr (March 2003–December 2005) of continuous particle number size distribution measurements have been conducted at the island of Uto in the Baltic Sea. The measured particle size range was from 7 to 530 nm. During the measurement period, a total of 103 regional new-particle formation events were observed. The characteristics of the nucleation events at Uto were similar to those reported in the literature in other Nordic sites, though measured condensation sinks were rather high (geometric mean of 3.8 × 10 -3 s -1 ) during event days. Clear evidence was found that new particles nucleate regionally near Uto, rather than are transported from greater distances. However, the Baltic Sea seems to have an inhibiting effect on new-particle formation. The boreal forest areas in the continental Finland were found to have an enhancing effect on the nucleation probability in Uto, suggesting that at least some of the precursor gases for nucleation and/or condensational growth of particles originate from these forests. In addition to regional new-particle formation events, a total of 94 local events were observed in Uto. These are short-lived events with a small footprint area, and can at least partly be tracked down to the emissions of ship traffic operating at Uto. DOI: 10.1111/j.1600-0889.2008.00343.x

Thirty months (March 2003–October 2005) of aerosol size distributions, trace gas and meteorological parameter measurements have been analysed at a background station in Baltic Sea. Log-normal modes have been fitted to the size distributions and a source region analysis using 120 h back trajectories has been accomplished. Seasonal and air mass influences have been studied and compared to other measurement sites. Only weak impacts of meteorological conditions have been found. New particle formation events were observed, but less frequently compared to continental sites, which is concluded being related to the lack of precursor gas sources close to the station and a higher condensation sink. The northeast Atlantic was recognized as an important source of particles in the Aitken mode. Especially in spring and summer, probably primary biogenic particles contribute largely to the particle number concentration. Source regions of the submicron aerosol are strongly dependant of the particle size and so is the contribution to the total number or mass concentration. For this reason, a consideration of the total number or mass concentration was identified not being sufficient in order to describe source areas of aerosol particles. DOI: 10.1111/j.1600-0889.2007.00285.x