Abstract.We have investigated the formation and early growth of atmospheric secondary aerosol particles building on atmospheric measurements. The measurements were part of the QUEST 2 campaign which took place in spring 2003 in Hyytiälä (Finland). During the campaign numerous aerosol particle formation events occurred of which 15 were accompanied by gaseous sulphuric acid measurements. Our detailed analysis of these 15 events is focussed on nucleation and early growth (to a diameter of 3 nm) of fresh particles. It revealed that new particle formation seems to be a function of the gaseous sulphuric acid concentration to the power from one to two when the time delay between the sulphuric acid and particle number concentration is taken into account. From the time delay the growth rates of freshly nucleated particles from 1 nm to 3 nm were determined. The mean growth rate was 1.2 nm/h and it was clearly correlated with the gaseous sulphuric acid concentration. We tested two nucleation mechanisms -recently proposed cluster activation and kinetic type nucleation -as possible candidates to explain the observed dependences, and determined experimental nucleation coefficients. We found that some events are dominated by the activation mechanism and some by the kinetic mechanism. Inferred coefficients for the two nucleation mechanisms are the same order of magnitude as chemical re-action coefficients in the gas phase and they correlate with the product of gaseous sulphuric acid and ammonia concentrations. This indicates that besides gaseous sulphuric acid also ammonia has a role in nucleation.

Abstract. As part of the work of the Economic Commission for Europe of the United Nations Task Force on Emission Inventories, a new set of guidelines has been developed for assessing the emissions of sulphur, nitrogen oxides, NH 3, CH4, and nonmethane volatile organic compounds (NMVOC) from biogenic and other natural sources in Europe. This paper gives the background to these guidelines, describes the sources, and gives our recommended methodologies for estimating emissions. We have assembled land use and other statistics from European or national compilations and present emission estimates for the various natural/biogenic source categories based on these.

Rates of monoterpene emissions from Scots pine (Pinus sylvestris) and Norwegian spruce (Picea abies) have been measured at four sites in Sweden with a dynamic flow chamber technique. Forest floor emissions have been made in the pine forest with the static chamber technique. Sampling was done with Tenax TA and analysis and detection by GC and ion trap detection. The compounds A 3-carene and a-pinene were the predominant terpenes emitted from the crown and floor of the Scots pine forest. Alpha-pinene was the main terpene emitted from Norwegian spruce at the sites in southern and central Sweden, while A 3-carene was predominant at the northern site. The relative composition of the emission of both species underwent changes in early spring and fall. Emission rates, normalized to temperature, were seen to vary diurnally with a maximum at midday, and seasonally with maxima in early May and October, and a summer maximum in June-July. The possible dependence of the emission rate on needle growth rate and other plant-physiological processes is discussed. A higher emission rate and different relative composition of the emission was seen to occur when the vegetation was wet, as compared to dry vegetation. The emission from the pine forest floor was seen to have a composition different from that of the crown and a seasonality of the rate similar to that of the crown. The ground emission could not be explained by sources in the litter or ground vegetation alone, and it is suggested that the root system of the trees is also an emission source. The emission rate from the pine forest floor was of the order of 30% of the crown emission. The July rate of emission from the crown of Scots pine, normalized to 20øC and averaged over four sites in Sweden, was 0.8 _+ 0.4 (gdw (grams dry weight) h) -1 , and for Norwegian spruce, 0.5 _ 0.7/xg(gdw h) -1 . It would seem that previous regional and global estimates of hydrocarbon fluxes to the atmosphere have used emission factors which are too high for boreal coniferous forests. 1. 1991]. All model studies are, however, in part thwarted by the gaps in our knowledge concerning the size and variation of natural hydrocarbon fluxes as well as their oxidation pathways and products. This is especially the case for the monoterpenes (hereafter referred to as the terpenes). The terpenes are acyclic, monocyclic, and bicyclic isomers of the formula C10H16, biosynthesized by many plant species, especially coniferous trees. Their flux to the atmosphere is estimated to be the largest, globally, of the natural nonmethane hydrocarbons (NMHCs) [Zimmerman et al., 1978; Altshuller, 1983]. As first reported by Tingey et al. [1978], the rate of their emission from conifers to the atmosphere varies exponentially with leaf temperature, similar to the temperature dependence of the terpene vapor pressures. Using the temperature dependencies reported in the literature for various coniferous species in different parts of the world, 20øC emission rates are seen to vary by 2 orders of magnitude, from 0.1 to about 10 •g ...

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