Summary Based on review and original data, this synthesis investigates carbon pools and fluxes of Siberian and European forests (600 and 300 million ha, respectively). We examine the productivity of ecosystems, expressed as positive rate when the amount of carbon in the ecosystem increases, while (following micrometeorological convention) downward fluxes from the atmosphere to the vegetation (NEE = Net Ecosystem Exchange) are expressed as negative numbers. Productivity parameters are Net Primary Productivity (NPP=whole plant growth), Net Ecosystem Productivity (NEP = CO2 assimilation minus ecosystem respiration), and Net Biome Productivity (NBP = NEP minus carbon losses through disturbances bypassing respiration, e.g. by fire and logging). Based on chronosequence studies and national forestry statistics we estimate a low average NPP for boreal forests in Siberia: 123 gC m–2 y–1. This contrasts with a similar calculation for Europe which suggests a much higher average NPP of 460 gC m–2 y–1 for the forests there. Despite a smaller area, European forests have a higher total NPP than Siberia (1.2–1.6 vs. 0.6–0.9 × 1015 gC region–1 y–1). This arises as a consequence of differences in growing season length, climate and nutrition.  For a chronosequence of Pinus sylvestris stands studied in central Siberia during summer, NEE was most negative in a 67‐y old stand regenerating after fire (– 192 mmol m–2 d–1) which is close to NEE in a cultivated forest of Germany (– 210 mmol m–2 d–1). Considerable net ecosystem CO2‐uptake was also measured in Siberia in 200‐ and 215‐y old stands (NEE:174 and – 63 mmol m–2 d–1) while NEP of 7‐ and 13‐y old logging areas were close to the ecosystem compensation point. Two Siberian bogs and a bog in European Russia were also significant carbon sinks (– 102 to – 104 mmol m–2 d–1). Integrated over a growing season (June to September) we measured a total growing season NEE of – 14 mol m–2 summer–1 (– 168 gC m–2 summer–1) in a 200‐y Siberian pine stand and – 5 mol m–2 summer–1 (– 60 gC m–2 summer–1) in Siberian and European Russian bogs. By contrast, over the same period, a spruce forest in European Russia was a carbon source to the atmosphere of (NEE: + 7 mol m–2 summer–1 = + 84 gC m–2 summer–1). Two years after a windthrow in European Russia, with all trees being uplifted and few successional species, lost 16 mol C m–2 to the atmosphere over a 3‐month in summer, compared to the cumulative NEE over a growing season in a German forest of – 15.5 mol m–2 summer–1 (– 186 gC m–2 summer–1; European flux network annual averaged – 205 gC m–2 y–1).  Differences in CO2‐exchange rates coincided with differences in the Bowen ratio, with logging areas partitioning most incoming radiation into sensible heat whereas bogs partitioned most into evaporation (latent heat). Effects of these different surface energy exchanges on local climate (convective storms and fires) and comparisons with the Canadian BOREAS experiment are discussed.  Following a classification of disturbances and their effects on ecosystem carb...

Abstract. Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March-April 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono-and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all parti-cles larger than 50 nm in diameter contained similar organic substances that are likely to be mono-and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10-50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP Published by Copernicus Publications on behalf of the European Geosciences Union. 2658A. Laaksonen et al.: VOC oxidation products and new particle formation concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3-10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.

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[1] Long-term measurements of sensible and latent heat and carbon dioxide fluxes were performed over a boreal lake in southern Finland using the direct micrometeorological eddy covariance (EC) technique. The water column was sampled weekly for dissolved carbon dioxide, and the CO 2 flux was estimated also applying the concentration gradient method. Temperature and oxygen profiles of the lake were measured twice a week. The measurements covered one full open-water period from April to November 2003, and it is the longest continuous CO 2 record ever measured over a lake by EC. The sensible heat flux H was positive, that is, from the lake to the atmosphere, except in May, when it was >0 W/m 2 at night and <0 W/m 2 in daytime. The latent heat flux dominated clearly over H in spring and summer; that is, the Bowen ratio was less than 1. Highermoment turbulence statistics proved to be efficient in detection of frequent nonstationary situations. Applying the statistical criteria for CO 2 concentration and vertical wind speed, averaging over a 5-min period and selecting only the wind direction with longest fetch, we could obtain lake-representative CO 2 fluxes. Footprint analysis based on a closure model revealed that the source areas were relatively short because of the presence of turbulence generated by the surrounding forest, compared to a larger lake with an extended smooth surface. We observed a net CO 2 source of 0.2-0.4 mmol m À2 s À1 excluding July, when the flux was closer to zero. The results are consistent with the gradient method, based on more infrequent sampling, and both methods gave the same average flux, 0.2 mmol m À2 s À1 , over the whole open-water period.

Abstract. On July 15 and 16, 1996, profiles of temperature, water vapor, carbon dioxide concentration, and its carbon isotopic composition were made within and above the convective boundary layer (CBL), near the village of Zotino in central Siberia (60øN, 89øE). On both days the CBL grew to a height of around 1000 m at midday after which little further growth was observed. This was despite high rates of sensible heat flux into the CBL from the predominantly coniferous vegetation below and was attributable to a high subsidence velocity. For all flights, marked discontinuities across the top of the CBL were observed for water vapor and CO2 concentrations with differences between the CBL and the free troposphere above being as high as 10 mmol mol -i and 13/xmol mo1-1, respectively. Associated with the lower CO2 concentrations within the CBL was an enrichment of the 6 13C in CO 2 of up to 0.7%o. Although for any one flight, fluctuations in CO2 and 6 13C within the CBL were small (less than 3/xmol mo1-1 and 0.1%o); they were well correlated and suggested a photosynthetic discrimination, A, by the vegetation below of -17%•. Estimates of regional A based on CBL budgeting techniques suggested values ranging from 14.8 to 20.4%•. CBL budgeting techniques were also used to estimate regional ecosystem carbon fluxes (-3 to -9/xmol m-2 s-i) and evaporation rates (1-3 mmol m -2 s-i). Agreement with ground-based tower measurements was reasonable, but a bootstrap error analysis suggested that errors associated with the integral CBL technique were sometimes unacceptably large, especially for estimates of regional photosynthetic 13C discrimination and regional evaporation rates.Conditions under which CBL techniques should result in reasonably accurate estimations of regional fluxes and isotopic fractionations are evaluated.

Abstract. We have modelled the total atmospheric OHreactivity in a boreal forest and investigated the individual contributions from gas phase inorganic species, isoprene, monoterpenes, and methane along with other important VOCs. Daily and seasonal variation in OH-reactivity for the year 2008 was examined as well as the vertical OHreactivity profile. We have used SOSA; a one dimensional vertical chemistry-transport model (Boy et al., 2011a) together with measurements from Hyytiälä, SMEAR II station, Southern Finland, conducted in August 2008. Model simulations only account for ∼30-50 % of the total measured OH sink, and in our opinion, the reason for missing OHreactivity is due to unmeasured unknown BVOCs, and limitations in our knowledge of atmospheric chemistry including uncertainties in rate constants. Furthermore, we found that the OH-reactivity correlates with both organic and inorganic compounds and increases during summer. The summertime canopy level OH-reactivity peaks during night and the vertical OH-reactivity decreases with height.

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A modification of the most popular two-equation (E-ϕ) models, taking into account the plant drag, is proposed. Here E is the turbulent kinetic energy (TKE) and ϕ is any of the following variables: El (product of E and the mixing length l), ε (dissipation rate of TKE), and ω (specific dissipation of TKE, ω = ε/E). The proposed modification is due to the fact that the model constants estimated experimentally for 'free-air' flow do not allow for adequate reconstruction of the ratio between the production and dissipation rates of TKE in the vegetation canopy and have to be adjusted. The modification is universal, i.e. of the same type for all E-ϕ models considered. The numerical experiments carried out for both homogeneous and heterogeneous plant canopies with E-ϕ models (and with the E-l model taken as a kind of reference) show that the modification performs well. They also suggest that E-ε and E-ω schemes are more promising than the E-El scheme for canopy flow simulation since they are not limited by the need to use a wall function.In addition, a new parameterization for enhanced dissipation within the plant canopy is derived. It minimizes the model sensitivity to C μ , the key parameter for two-equation schemes, and whose estimates unfortunately vary considerably from experiment to experiment. The comparison of results of new modified E-ε and E -ω models with observations from both field and wind-tunnel experiments shows that the proposed parameterization is quite robust. However, because of uncertainties with the turbulence Prandtl and Schmidt numbers for the E-ε model within the canopy, the E-ω model is recommended for future implementation, with the suggested modifications.