ISSN 1239-6095
© Boreal Environment Research 2005

Contents of Volume 10 Number 5

Hari, P. & Kulmala, M. 2005: Station for Measuring Ecosystem–Atmosphere Relations (SMEAR II). Boreal Env. Res. 10: 315–322.
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Dal Maso, M., Kulmala, M., Riipinen, I., Wagner, R., Hussein, T., Aalto, P. P. & Lehtinen, K. E. J. 2005: Formation and growth of fresh atmospheric aerosols: eight years of aerosol size distribution data from SMEAR II, Hyytiälä, Finland. Boreal Env. Res. 10: 323–336.
Abstract
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Hussein, T., Dal Maso, M., Petäjä, T., Koponen, I. K., Paatero, P., Aalto, P. P., Hämeri, K. & Kulmala, M. 2005: Evaluation of an automatic algorithm for fitting the particle number size distributions. Boreal Env. Res. 10: 337–355.
Abstract
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Hirsikko, A., Laakso, L, Hõrrak, U., Aalto, P. P., Kerminen, V.-M. & Kulmala, M. 2005: Annual and size dependent variation of growth rates and ion concentrations in boreal forest. Boreal Env. Res. 10: 357–369.
Abstract
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Anttila, P., Rissanen, T., Shimmo, M., Kallio, M., Hyötyläinen, T., Kulmala, M. & Riekkola, M.-L. 2005: Organic compounds in atmospheric aerosols from a Finnish coniferous forest. Boreal Env. Res. 10: 371–384.
Abstract
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Saarikoski, S., Mäkelä, T., Hillamo, R., Aalto, P. P., Kerminen, V.-M. & Kulmala, M. 2005: Physico-chemical characterization and mass closure of size-segregated atmospheric aerosols in Hyytiälä, Finland. Boreal Env. Res. 10: 385–400.
Abstract
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Ilvesniemi, H., Kähkönen, M. A., Pumpanen, J., Rannik, Ü., Wittmann, C., Perämäki, M., Keronen, P., Hari, P., Vesala, T. & Salkinoja-Salonen, M. 2005: Wintertime CO2 evolution from a boreal forest ecosystem. Boreal Env. Res. 10: 401–408.
Abstract
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Bäck, J., Hari, P., Hakola, H., Juurola, E. & Kulmala, M. 2005: Dynamics of monoterpene emissions in Pinus sylvestris during early spring. Boreal Env. Res. 10: 409–424.
Abstract
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Rinne, J., Ruuskanen, T. M., Reissell, A., Taipale, R., Hakola, H. & Kulmala, M. 2005: On-line PTR-MS measurements of atmospheric concentrations of volatile organic compounds in a European boreal forest ecosystem. Boreal Env. Res. 10: 425–436.
Abstract
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Sevanto, S., Hölttä, T., Hirsikko, A., Vesala, T. & Nikinmaa, E. 2005: Determination of thermal expansion of green wood and the accuracy of tree stem diameter variation measurements. Boreal Env. Res. 10: 437–445.
Abstract
Full text (pdf format)

Sevanto, S., Hölttä, T., Markkanen, T., Perämäki, M., Nikinmaa, E. & Vesala, T. 2005: Relationships between diurnal xylem diameter variation and environmental factors in Scots pine. Boreal Env. Res. 10: 447–458.
Abstract
Full text (pdf format)


Hari, P. & Kulmala, M. 2005: Station for Measuring Ecosystem–Atmosphere Relations (SMEAR II). Boreal Env. Res. 10: 315–322.

Here we present the ongoing SMEAR (Station for Measuring Forest Ecosystem–Atmosphere Relations) research program and also related future views. The main idea of SMEAR-type infrastructures is continuous, comprehensive measurements of fluxes, storages and concentrations in the land ecosystem–atmosphere continuum. The major coupling mechanisms between atmosphere and land surface are the fluxes of energy, momentum, water, carbon dioxide, atmospheric trace gases and atmospheric aerosols. Understanding of couplings and feedbacks is the basis for the prediction of changes in the system formed by atmosphere, vegetation and soil. A better quantification of the agents that cause climate change, as well as the emissions and removals of species, will provide more accurate projections of future atmospheric composition and hence climate.
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Dal Maso, M., Kulmala, M., Riipinen, I., Wagner, R., Hussein, T., Aalto, P. P. & Lehtinen, K. E. J. 2005: Formation and growth of fresh atmospheric aerosols: eight years of aerosol size distribution data from SMEAR II, Hyytiälä, Finland. Boreal Env. Res. 10: 323–336.

We analyzed size distributions measured continuously at a boreal forest measurement site at Hyytiälä, Finland between 1996 and 2003. From the eight-year data we identified days when new aerosol particle formation was taking place as well as days when no formation was detected, removing days with ambiguous status. The event days were then classified based on whether it was possible to determine formation and growth rates of new particles. These characteristics were then calculated. We found that new particle formation happens frequently in the boreal forest boundary layer, with at least 24% of days containing an event. Events are more probable during spring and autumn than during other times of the year. The average formation rate of particles larger than 3 nm was 0.8 cm–3 s–1, with enhanced rates during spring and autumn. The mean growth rate was 3.0 nm h–1, peaking in summer. The created event database is valuable for future studies of reasons leading to new particle formation in the atmosphere.
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Hussein, T., Dal Maso, M., Petäjä, T., Koponen, I. K., Paatero, P., Aalto, P. P., Hämeri, K. & Kulmala, M. 2005: Evaluation of an automatic algorithm for fitting the particle number size distributions. Boreal Env. Res. 10: 337–355.

The multi log-normal distribution function is widely in use to parameterize the aerosol particle size distributions. The main purpose of such a parameterization is to quantitatively describe size distributions and to allow straightforward comparisons between different aerosol particle data sets. In this study, we developed and evaluated an algorithm to parameterize aerosol particle number size distributions with the multi log-normal distribution function. The current algorithm is automatic and does not need a user decision for the initial input parameters; it requires only the maximum number of possible modes and then it reduces this number, if possible, without affecting the fitting quality. The reduction of the number of modes is based on an overlapping test between adjacent modes. The algorithm was evaluated against a previous algorithm that can be considered as a standard procedure. It was also evaluated against a long-term data set and different types of measured aerosol particle size distributions in the ambient atmosphere. The evaluation of the current algorithm showed the following advantages: (1) it is suitable for different types of aerosol particles observed in different environments and conditions, (2) it showed agreement with the previous standard algorithm in about 90% of long-term data set, (3) it is not time-consuming, particularly when long-term data sets are analyzed, and (4) it is a useful tool in the studies of atmospheric aerosol particle formation and transformation.
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Hirsikko, A., Laakso, L, Hõrrak, U., Aalto, P. P., Kerminen, V.-M. & Kulmala, M. 2005: Annual and size dependent variation of growth rates and ion concentrations in boreal forest. Boreal Env. Res. 10: 357–369.

Number size distributions of particles and ions were measured with a differential mobility particle sizer and two different ion spectrometers at the SMEAR II station in southern Finland during April 2003–April 2004. Cluster ion (diameter < 1.6 nm) concentrations varied between 200 and 1500 cm–3, while the concentrations of intermediated ions (1.6–6.3 nm) remained usually below 200 cm–3. During the 70 observed nucleation event days, particle growth rates were strongly dependent on their size. The median diameter growth rates of particles in size classes 7–20 nm, 3–7 nm and 1.3–3 nm were 4–5 nm h–1, 2–4 nm h–1 and < 2 nm h–1, respectively. The growth rates of the smallest ions/particles were almost independent of the season having a minimum during the summer, whereas the growth rates of larger particles had a clear annual cycle with the highest values during the summer and lowest values during the winter. The results indicate that in addition to sulphuric acid, compounds related to photosynthesis participate in the particle growth, especially in the size class 7–20 nm.
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Anttila, P., Rissanen, T., Shimmo, M., Kallio, M., Hyötyläinen, T., Kulmala, M. & Riekkola, M.-L. 2005: Organic compounds in atmospheric aerosols from a Finnish coniferous forest. Boreal Env. Res. 10: 371–384.

Atmospheric aerosol particles were collected with a high-volume sampler in a Finnish coniferous forest during the field campaign Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST) in March–April 2003. Four chromatographic techniques were applied to characterise the organic composition of the samples, and to study variations in the concentrations of identified compounds. Among the nearly 160 organic compounds identified were n-alkanes, n-alkanals, n-alkan-2-ones, n-alkanols, n-alkanoic acids, n-alkenoic acids, dicarboxylic acids, polyaromatic hydrocarbons, hopanes, streranes, terpenes and terpenoids. The observed variations in the concentrations of certain compounds were mostly explained by ambient temperature. Comparison of days when atmospheric new particle formation took place with days when the formation did not occur, however, revealed higher concentrations of long-chain n-alkanes (> C22) and < C18 n-alkanoic acids on the particle formation days.
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Saarikoski, S., Mäkelä, T., Hillamo, R., Aalto, P. P., Kerminen, V.-M. & Kulmala, M. 2005: Physico-chemical characterization and mass closure of size-segregated atmospheric aerosols in Hyytiälä, Finland. Boreal Env. Res. 10: 385–400.

A size-segregated chemical composition of atmospheric aerosols was investigated in May 2004 at the SMEAR II station, southern Finland. Aerosols were collected using two 12-stage low pressure impactors (SDI) and two virtual impactors (VI). The samples were analyzed for mass, inorganic ions and organic (OC) and elemental carbon (EC). By comparing the gravimetric mass and the results from the chemical analyses, a chemical mass closure was constructed. In addition to the impactors an Electrical Low Pressure Impactor (ELPI), Differential Mobility Particle Sizer (DMPS) and Aerodynamic Particle Sizer (APS) were used to measure the mass size distribution continuously. The chemical composition of fine particles (particle diameter < 1 um) was very similar over the whole measurement campaign with 40% of mass composed of ammonium sulfate, 35% of OC and 5% of EC. In the submicron range the chemical mass closure of the collected samples was reached within a few percent on average. The chemical mass to gravimetric mass ratio was 0.98 ± 0.10 and 1.05 ± 0.13 (average ± S.D.) for the VI and SDI, respectively. Also, quite a good agreement was obtained between the mass size distributions measured with the ELPI and that measured with the DMPS-APS combination. When the total mass concentration of the fine particles was calculated, the mass concentration of the ELPI was found to be larger than that of the SDI and VI (ELPI/VI ratio 1.11 ± 0.13). This may be due to the semivolatile components lost in impactors. For the SDI and DMPS-APS the concentration of the fine particles was smaller than that of the VI with the SDI/VI and DMPS-APS/VI ratios of 0.70 ± 0.11 and 0.92 ± 0.08, respectively. For the DMPS and APS the mass concentration was calculated from the number concentration by estimating the particle density. The particle density was assessed in two ways; from the chemical composition of the particles (composite density) and by comparing the mass obtained from the DMPS-APS combination with the VI mass concentration (gravimetric density). The densities obtained for fine particles were 1.49 ± 0.03 and 1.66 ± 0.13 g cm–3 for the composite and gravimetric density, respectively.
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Ilvesniemi, H., Kähkönen, M. A., Pumpanen, J., Rannik, Ü., Wittmann, C., Perämäki, M., Keronen, P., Hari, P., Vesala, T. & Salkinoja-Salonen, M. 2005: Wintertime CO2 evolution from a boreal forest ecosystem. Boreal Env. Res. 10: 401–408.

We investigated wintertime ecosystem activity and CO2 efflux over three winters (1 November–28 February 1997–2000) in a boreal Scots pine stand in Finland. During the three winters the cumulative wintertime CO2 efflux measured with continuously operating soil chambers directly from the soil surface was between 103 and 144 g m–2, and between 240 and 330 g m–2 when measured by an eddy covariance method or estimated from the soil sample endogenous CO2 production. The flux measured directly from the soil surface is probably an underestimation due to the ice formation within the chamber. Photosynthesis was found to be active also during winter and metabolic activity was found to show extrapolated zero at –5 °C to –10 °C.
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Bäck, J., Hari, P., Hakola, H., Juurola, E. & Kulmala, M. 2005: Dynamics of monoterpene emissions in Pinus sylvestris during early spring. Boreal Env. Res. 10: 409–424.

The seasonal dynamics of biogenic volatile organic compound (BVOC) emissions, which can be related to the formation and growth of secondary organic aerosols, represent an important but at the present poorly understood linkage between vegetation activity and climate. Although a close relationship between photosynthesis and terpenoid emissions has been proposed, high monoterpene emission rates for Scots pine shoots (Pinus sylvestris) are frequently recorded during spring, in times when photosynthetic activity is strongly inhibited due to inherent seasonal restrictions. We suggest that terpenoid emissions are related to either photosynthesis or photorespiration for precursors for terpenoid biosynthesis. We developed two dynamic models describing temporal fluctuations in Scots pine monoterpene emissions, calculating the emissions by using CO2 exchange and ambient climate data. The models accurately predicted the measured monoterpene flux, and especially in March–April, during the time when photosynthesis was negligible and ambient temperatures were between –5 and +15 °C, a good agreement was found with measured emissions and the model involving photorespiration.
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Rinne, J., Ruuskanen, T. M., Reissell, A., Taipale, R., Hakola, H. & Kulmala, M. 2005: On-line PTR-MS measurements of atmospheric concentrations of volatile organic compounds in a European boreal forest ecosystem. Boreal Env. Res. 10: 425–436.

On-line measurements of atmospheric VOC concentrations in the European boreal zone with a proton transfer reaction mass spectrometer were conducted at SMEAR II station in Hyytiälä, south-western Finland on 2–22 July 2004. The measurements showed a strong diurnal variation of several compounds. A factor analysis performed for the concentration data was used to classify the measured VOC masses into three classes based on the behavior of their concentrations. The masses in the first class had a high diurnal variation with maximum values in the afternoon. Compounds contributing to masses in this category were e.g. methanol, acetone, methyl-vinyl-ketone and hexanal. The concentrations of masses in the second class had also a high diurnal variation, but with maxima during the night when the mixing of the atmospheric surface layer was weak. Monoterpenes and phenol are compounds contributing to the masses in this category. The masses in the third class did not have a marked diurnal cycle and were not dependent on the local meteorological parameters. The masses having a strong positive loading on this factor were those associated with anthropogenic compounds with relatively long atmospheric life-times, such as benzene. Considering the difference in the measurement height, the total monoterpene concentration measured by the PTR-MS was consistent with the concentration measured by gas chromatography-mass spectrometer with adsorbent sampling.
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Sevanto, S., Hölttä, T., Hirsikko, A., Vesala, T. & Nikinmaa, E. 2005: Determination of thermal expansion of green wood and the accuracy of tree stem diameter variation measurements. Boreal Env. Res. 10: 437–445.

The coefficient of thermal expansion in the radial direction for wet fresh wood was determined for two coniferous species Pinus sylvestris and Picea abies and three broad-leaved species Acer platanoides, Betula pendula and Alnus incana. The diameter variation of 7–11 samples of each species was measured in a water heat bath with a linear variable displacement transducer (LVDT). The temperature range was 5–45 °C. The average values for the coefficient of thermal expansion varied between 7.9 x 10–6 and 17.5 x 10–6 °C–1. Heating and cooling gave similar results for all the species and no hysteresis was observed. The results show that the coefficient of thermal expansion for wet green wood is a positive number as for dry wood and timber, contrary to values mentioned in literature. The coefficient is lower than that of dry timber and of the same order of magnitude as the coefficient of many commonly used metals and alloys. In field measurements of tree stem diameter variations an LVDT is usually attached to a metal frame. The similar magnitude of the coefficients means that the accuracy of absolute values of tree stem diameter variations is dominated by the temperature difference between the stem and the surrounding air. However, if both the temperatures are measured, the error in stem diameter variation measurements resulting from the thermal expansion can be corrected.
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Sevanto, S., Hölttä, T., Markkanen, T., Perämäki, M., Nikinmaa, E. & Vesala, T. 2005: Relationships between diurnal xylem diameter variation and environmental factors in Scots pine. Boreal Env. Res. 10: 447–458.

We analyzed the variability in diurnal xylem diameter in Scots pine (Pinus sylvestris) by comparing daily maximum, minimum and average diameters and daily amplitudes of variation with environmental variables related to transpiration and water uptake from the soil. The measurements were carried out during six summers, 1999–2004 at SMEAR II station in Hyytiälä, southern Finland. We found that the daily maximum, minimum and average diameters and amplitudes were closest related to daily average water vapor deficits (VPD) and soil water contents in A-horizon ([theta]A). However, the highest degree of determination was only 37%. That was found for daily minimum diameter by VPD. The degree of determination and correlation could be improved by making up variables that took into account the variation in factors related to transpiration and soil water availability. In that case the highest correlation (negative correlation) and coefficient of determination was found for daily minimum diameter by VPD scaled with [theta]A so that VPD was enhanced when soil water content was low (VPD* = VPD*([theta]Amin/[theta]A)). This could explain 50% of the variation in daily minimum diameters. The results emphasize the importance of both inflow- and outflow-related factors in explaining the water tension and water status of tree stems.
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