ISSN 1239-6095
© Boreal Environment Research 2003

Contents of Volume 8 Number 4

Preface: Climate–biOspheRE Interactions (CORE). Boreal Env. Res. 8: 273.
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Kurtén, T., Kulmala, M., Dal Maso, M., Suni, T., Reissell, A., Vehkamäki, H., Hari, P., Laaksonen, A., Viisanen, Y. & Vesala, T. 2003: Estimation of different forest-related contributions to the radiative balance using observations in southern Finland. Boreal Env. Res. 8: 275–285.
Abstract
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Suni, T., Rinne, J., Reissell, A., Altimir, N., Keronen, P., Rannik, Ü., Dal Maso, M., Kulmala, M. & Vesala, T. 2003: Long-term measurements of surface fluxes above a Scots pine forest in Hyytiälä, southern Finland, 1996–2001. Boreal Env. Res. 8: 287–301.
Abstract
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Jennings, S. G., Kleefeld, C., O'Dowd, C. D., Junker, C., Spain, T. G., O'Brien, P., Roddy, A. F. & O'Connor, T. C. 2003: Mace Head Atmospheric Research Station — characterization of aerosol radiative parameters. Boreal Env. Res. 8: 303–314.
Abstract
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Pilegaard, K., Mikkelsen, T. N., Beier, C., Jensen, N. O., Ambus, P. & Ro-Poulsen, H. 2003: Field measurements of atmosphere–biosphere interactions in a Danish beech forest. Boreal Env. Res. 8: 315–333.
Abstract
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Ruuskanen, T. M., Reissell, A., Keronen, P., Aalto, P. P., Laakso, L., Grönholm, T., Hari, P. & Kulmala, M. 2003: Atmospheric trace gas and aerosol particle concentration measurements in Eastern Lapland, Finland 1992–2001. Boreal Env. Res. 8: 335–349.
Abstract
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Virkkula, A., Teinilä, K., Hillamo, R. & Stohl, A. 2003: A decade of trace gas measurements using DOAS in Finnish Lapland. Boreal Env. Res. 8: 351–363.
Abstract
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Hatakka, J., Aalto, T., Aaltonen, V., Aurela, M., Hakola, H., Komppula, M., Laurila, T., Lihavainen, H., Paatero, J., Salminen, K. & Viisanen, Y. 2003: Overview of the atmospheric research activities and results at Pallas GAW station. Boreal Env. Res. 8: 365–383.
Abstract
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Aalto, T., Hatakka, J. & Viisanen, Y. 2003: Influence of air mass source sector on variations in CO2 mixing ratio at a boreal site in northern Finland. Boreal Env. Res. 8: 385–393.
Abstract
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Komppula, M., Dal Maso, M., Lihavainen, H., Aalto, P. P., Kulmala, M. & Viisanen, Y. 2003: Comparison of new particle formation events at two locations in northern Finland. Boreal Env. Res. 8: 395–404.
Abstract
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Lehtinen, K. E. J., Korhonen, H., Dal Maso, M. & Kulmala, M. 2003: On the concept of condensation sink diameter. Boreal Env. Res. 8: 405–411.
Abstract
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Kokkola, H., Romakkaniemi, S., Kulmala, M. & Laaksonen, A. 2003: A cloud microphysics model including trace gas condensation and sulfate chemistry. Boreal Env. Res. 8: 413–424.
Abstract
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Keronen, P., Reissell, A., Rannik, Ü., Pohja, T., Siivola, E., Hiltunen, V., Hari, P., Kulmala, M. & Vesala, T. 2003: Ozone flux measurements over a Scots pine forest using eddy covariance method: performance evaluation and comparison with flux-profile method. Boreal Env. Res. 8: 425–443.
Abstract
Full text (pdf format)

Raivonen, M., Keronen, P., Vesala, T., Kulmala, M. & Hari, P. 2003: Measuring shoot-level NOx flux in field conditions: the role of blank chambers. Boreal Env. Res. 8: 445–455.
Abstract
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Sevanto, S., Mikkelsen, T. N., Pilegaard, K. & Vesala, T. 2003: Comparison of tree stem diameter variations in beech (Fagus sylvatica L.) in Sorø Denmark and in Scots pine (Pinus sylvestris L.) in Hyytiälä, Finland. Boreal Env. Res. 8: 457–464.
Abstract
Full text (pdf format)


Kurtén, T., Kulmala, M., Dal Maso, M., Suni, T., Reissell, A., Vehkamäki, H., Hari, P., Laaksonen, A., Viisanen, Y. & Vesala, T. 2003: Estimation of different forest-related contributions to the radiative balance using observations in southern Finland. Boreal Env. Res. 8: 275–285.

The effect of boreal forest on the Earth's energy budget was estimated in field conditions in Hyytiälä, southern Finland. The indirect aerosol effect due to new particle formation, the effect of forest carbon sequestration and the effect of forestation- or deforestation-related albedo change were investigated. The young, fast-growing boreal forest was estimated to be a relatively significant carbon sink and an important aerosol source, and thus the effect on the Earth's energy budget was seen to be negative. The estimated values (reported as annually averaged energy budget perturbations per square meter of forest) were –36 W m–2 due to the carbon sink, +10 W m–2 due to the albedo effect and between –5 and –14 W m–2 due to the aerosol effect. However, the values are uncertain.
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Suni, T., Rinne, J., Reissell, A., Altimir, N., Keronen, P., Rannik, Ü., Dal Maso, M., Kulmala, M. & Vesala, T. 2003: Long-term measurements of surface fluxes above a Scots pine forest in Hyytiälä, southern Finland, 1996–2001. Boreal Env. Res. 8: 287–301.

We present nearly six years of measurements of surface fluxes of momentum, sensible heat, water vapour, carbon dioxide and aerosol particles, along with a three-month time series of ozone flux, measured by eddy covariance above a Scots pine forest in southern Finland from April 1996 to December 2001. The results show marked seasonal and diurnal variation and a significant effect of local and remote anthropogenic pollution on CO2 and particle data. The flux of inert CO2 followed environmental factors through plant and soil-microbe metabolism very closely. The flux of reactive O3 depended on the overlapping influences of environmental parameters driving photosynthesis and of the available amount of reaction partners. The flux of multireactive aerosol particles showed no clear connection with any environmental variable. On new-particle-formation days, the average deposition velocity of particles was, however, greater than usual because small nucleation-mode particles have greater deposition velocities than do larger accumulation-mode particles.
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Jennings, S. G., Kleefeld, C., O'Dowd, C. D., Junker, C., Spain, T. G., O'Brien, P., Roddy, A. F. & O'Connor, T. C. 2003: Mace Head Atmospheric Research Station — characterization of aerosol radiative parameters. Boreal Env. Res. 8: 303–314.

A fairly concise description and a short history of the Mace Head atmospheric research station, at 53°N, 10°W, on the west coast of Ireland is reported. The relatively high latitude site is representative of background marine air in the Northern Atlantic on the western periphery of Europe. The site is ideally located to measure the prevailing (about 52% of the time) westerly-southwesterly air from the Atlantic, as well as polluted air under anticyclonic conditions from sources east of the site within Ireland, from the UK and from mainland Europe. Three years of aerosol radiative data, over a period from January 2000 to December 2002, are indicative of the medium to longterm measurement programme at the site. These include aerosol scattering coefficient, aerosol absorption coefficient, aerosol optical depth and single scattering albedo, supported by meteorological and air mass trajectory input. Variability in aerosol parameters are shown to be dependent on air mass origin, season and meteorological conditions. Measurements indicate that the dominant contribution to aerosol optical depth is due to scattering, with single scattering albedo in the range 0.941 to 0.997. Measured aerosol optical depth for marine air over the 3 year period varies between 0.03 and 0.38 with a mean value of 0.11 and standard deviation of +/-0.06. These values are in fair agreement with other data for the North Atlantic region.
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Pilegaard, K., Mikkelsen, T. N., Beier, C., Jensen, N. O., Ambus, P. & Ro-Poulsen, H. 2003: Field measurements of atmosphere–biosphere interactions in a Danish beech forest. Boreal Env. Res. 8: 315–333.

A field station was established in a beech forest near Sorø, Denmark in the spring of 1996 to provide a platform for studies of atmosphere–biosphere interactions. The station is equipped with a 57-m mast and a 24-m scaffolding tower. The mast makes it possible to measure profiles of gaseous atmospheric compounds and meteorological variables and to undertake measurements of fluxes by the eddy covariance method. The tower gives access to the tree canopy where branch and leaf level exchange of water vapour and CO2 is measured. Soil-atmosphere exchange of gaseous compounds is investigated with gas flux chambers on the soil surface. Water-mediated transport of C and N is measured in throughfall, stemflow and soil water. The paper provides information on the site, vegetation, climate and soil and gives a description of the instrumentation and other technical installations at the site. The paper also presents and discusses example results from the measurements such as meteorological variables (temperature, wind speed, wind direction, radiation, rainfall and relative humidity), gaseous concentrations (O3) and fluxes (CO2, CH4 and N2O), water mediated transport (NO3 and NH4+ in rainfall, throughfall, stemflow and soil water) and measurements on the trees (leaf area index, specific leaf area, litter fall, CO2 exchange at branch and leaf level, maximum photosynthetic capacity). The forest acted in all years as a carbon sink with an average uptake of 190 g C m–2 yr–1. Contributions from CH4 and N2O in terms of global warming potential (GWP) were less than 10% of the CO2. CH4 was deposited and N2O emitted, almost neutralising each other in terms of GWP. Leaves at the top of the canopy had the highest photosynthetic capacity (mid summer maximum of 50 umol m–2 s–1) and leaves at the bottom the lowest (20 umol m–2 s–1), indicating a clear acclimation to light. Sun leaves generally had significantly lower specific leaf area (118 cm2 g–1) and water content (42%) than shade leaves (specific leaf area: 282 cm2 g–1; water content: 53%). On an annual basis about 24% of the precipitation was lost as evaporation, 66% reached the forest floor as throughfall and 10% as stemflow. Due to leaching of NO3 from the trees, the forest floor received 30% more nitrogen than in precipitation, resulting in a total input of 2.9 g N m–2 yr–1). The soil water was almost completely depleted in NO3 with NH4+ constituting 97% of the total available inorganic nitrogen.
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Ruuskanen, T. M., Reissell, A., Keronen, P., Aalto, P. P., Laakso, L., Grönholm, T., Hari, P. & Kulmala, M. 2003: Atmospheric trace gas and aerosol particle concentration measurements in Eastern Lapland, Finland 1992–2001. Boreal Env. Res. 8: 335–349.

Trace gases (SO2, NOx, O3) and aerosol particles alongside with meteorological parameters have been measured continuously since 1992 in a remote Arctic station in Värriö, Finnish Lapland. In this background region there are practically no local sources of pollution. The goal of this study was to investigate the transport of gaseous pollutants and aerosol particles to a remote area. The seasonal, diurnal and long-term behaviour of trace gases and aerosol particles is presented as well as their correlation with each other and with local wind direction. A slightly diminishing trend was observed for low summertime ozone (O3) concentrations from 1995 to 2001. No distinct long-term trends for other species were noted. The monthly-medium concentrations were highest for SO2 and NOx in the winter, for ozone in the spring and for aerosol particles in the summer. The cleanest air seemed to arrive with northwesterly local winds, whereas the most polluted air was associated with easterly local winds and occurred as short episodes.
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Virkkula, A., Teinilä, K., Hillamo, R. & Stohl, A. 2003: A decade of trace gas measurements using DOAS in Finnish Lapland. Boreal Env. Res. 8: 351–363.

Trace gas concentrations have been measured at Sevettijärvi in Finnish Lapland from 8 January 1992 to 10 July 2002. The maximum hourly SO2 concentrations decreased from around 500 ug m–3 in the first two years of the monitoring to 200–300 ug m–3 in the mid 1990s. The annual average SO2 concentrations decreased from about 5 ug m–3 to 3–4 ug m–3 during the same period when taking into account the years for which the data coverage was above 85%. For NO2 and O3 no clear trends were observed. The sources of all three trace gases were investigated using wind measurements and in the case of NO2 also using back trajectories. The analysis indicated that the source areas of NO2 and SO2 are to the east and north-east of the site, i.e., at Nikel-Zapolyarnyj industrial areas in Kola Peninsula, Russia. In addition to these, NO2 transported from other industrial and urban areas in Europe can also be observed at Sevettijärvi.
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Hatakka, J., Aalto, T., Aaltonen, V., Aurela, M., Hakola, H., Komppula, M., Laurila, T., Lihavainen, H., Paatero, J., Salminen, K. & Viisanen, Y. 2003: Overview of the atmospheric research activities and results at Pallas GAW station. Boreal Env. Res. 8: 365–383.

Finnish Meteorological Institute's air quality measuring station at Pallas, in northern Finland, has been part of the Global Atmosphere Watch programme of the World Meteorological Organization since 1994. Tropospheric air composition and meteorological measurements are made at four different locations. Measured components include greenhouse and reactive gases, volatile organic compounds, chemistry of precipitation and aerosols, radon, carbon dioxide flux, meteorological parameters and a number of different aerosol characteristics. Pallas has proven to be a good site for measuring continental background air. This paper gives a general overview of the Pallas GAW station measurement sites and methods, and extensive overview of the scientific results.
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Aalto, T., Hatakka, J. & Viisanen, Y. 2003: Influence of air mass source sector on variations in CO2 mixing ratio at a boreal site in northern Finland. Boreal Env. Res. 8: 385–393.

CO2 mixing ratio in air masses coming from different source sectors was studied at Pallas measurement station in Lapland. Source sectors were defined using back trajectories and wind direction measurements. Air masses from the North and West sectors showed an annual variation of 17 ppm, possibly affected by a long range transported marine air. A larger variation of 20 ppm was observed in air masses from the more continental South and East sectors. During late autumn mixing ratios in air masses from the South sector were high in comparison with the other sectors. Different methods for a source sector definition were considered for the site, located in a contoured terrain. 52%–73% of wind direction-based source sector definitions agreed with trajectory-based definitions. However, the number of cases with reliable sector definitions may remain low when considering all observations. Different definition methods can cause differences of the order of 1 ppm in sectorially selected monthly mean CO2 mixing ratios.
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Komppula, M., Dal Maso, M., Lihavainen, H., Aalto, P. P., Kulmala, M. & Viisanen, Y. 2003: Comparison of new particle formation events at two locations in northern Finland. Boreal Env. Res. 8: 395–404.

During 21 months (April 2000–December 2001) of continuous aerosol particle number size distribution measurements in a subarctic area in northern Finland over 90 new particle formation events were observed. Measurements were done at two stations separated from each other by 250 kilometres. The Pallas station is located in western Lapland and Värriö station in eastern Lapland. New particle formation events were compared between the stations. Trajectories, trace gas concentrations and various weather parameters were investigated to explain the reasons for observed differences. According to trajectory analyses, all events were associated with marine/polar air masses originating from the northern Atlantic or the Arctic Ocean. 55% of particle formation events were observed at the same day on both sites, while on 45% of the cases particle formation was observed only at one of the stations. Most of these differences were explained by air masses of different origin or rain/fog on the other station. Among events observed only at the Värriö site, experiencing air masses from Kola Peninsula industrial area, about 80% were associated with high SO2 concentrations. At the Pallas site no increase in SO2 concentrations was observed. This is an indication that in plumes originating from the Kola industrial area, new particles are formed by nucleation involving H2SO4 from SO2 oxidation. The distance from Kola Peninsula to Pallas is long enough to reduce the SO2 concentration level lower than needed to launch the nucleation process at Pallas. Also on some occasions the air masses arriving at Pallas had been reasonably higher up in the atmosphere as compared with air masses at the site closer to Kola Peninsula. Air masses at higher altitudes are not influenced so much by the Kola industry. Based on this work about one third of the nucleation events observed at Värriö are effected or caused by the Kola Peninsula industry.
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Lehtinen, K. E. J., Korhonen, H., Dal Maso, M. & Kulmala, M. 2003: On the concept of condensation sink diameter. Boreal Env. Res. 8: 405–411.

The condensation sink has turned out to be a useful concept in the evaluation of atmospheric aerosol dynamics. Particularly, using growth rates together with the condensation sink will help understanding the formation and growth processes of atmospheric aerosols. In this paper, we develop this formalism even further and introduce the concept of condensation sink diameter (CSD). It can be successfully used both when analyzing experimental data as well as in model calculations, especially when using simple multimodal monodisperse methods. The observed values of CSD for the whole distribution in Hyytiälä are seen to be of the order 100 nm. The connection between number median diameter, surface area diameter and CSD is investigated in depth as well as the role of the CSD when designing model runs of atmospheric particle formation and growth.
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Kokkola, H., Romakkaniemi, S., Kulmala, M. & Laaksonen, A. 2003: A cloud microphysics model including trace gas condensation and sulfate chemistry. Boreal Env. Res. 8: 413–424.

A one-dimensional model for simulating the evolution of physical and chemical properties of an aerosol population has been developed in order to simulate cloud or fog droplet formation. The physicochemical processes affecting the aerosol population and included in the model are condensation and evaporation of water vapor and trace gases, gas emissions, and reversible and irreversible chemical reactions producing sulfate in the liquid phase. The model also includes modules for equilibrating the aerosol population with water vapor and trace gases, and for calculating the optical properties of the aerosol population. In this article, we compare the model results with other cloud models, and show that very similar fractions of activated particles are obtained using the thermodynamical models EQUISOLV II and AIM. We point out that when ammonia and strong acids (nitric and/or hydrochloric) are present in the system, the methods for the initial equilibration of the semi-volatile compounds can have a significant effect on the simulation results. We also compare the effects of nitric and hydrochloric acid with cloud drop activation and study sulfate production in the presence and in the absence of condensable trace gases.
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Keronen, P., Reissell, A., Rannik, Ü., Pohja, T., Siivola, E., Hiltunen, V., Hari, P., Kulmala, M. & Vesala, T. 2003: Ozone flux measurements over a Scots pine forest using eddy covariance method: performance evaluation and comparison with flux-profile method. Boreal Env. Res. 8: 425–443.

Ozone fluxes were measured over a forest in southern Finland between August 2001 and July 2002 using the eddy covariance method. Systematic errors due to the imperfect frequency response of the instrumentation and random errors due to the stochastic nature of turbulence were estimated. Flux underestimation correction factors for unstable stratification were 1.03–1.19. Random errors of the flux estimates were most frequently about 20% of the flux value. Fluxes were highest during the summer, declining to near zero during the winter. In summer, fluxes were higher during daytime than at night coinciding with higher turbulence and higher rate of stomatal uptake. Maximum summertime deposition velocities were 6–7 mm s–1. During winter, the diurnal pattern in ozone flux was weak and the deposition velocity was 0.5–1.5 mm s–1. Comparison between eddy covariance and profile flux measurement results generally showed good agreement during daytime.
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Raivonen, M., Keronen, P., Vesala, T., Kulmala, M. & Hari, P. 2003: Measuring shoot-level NOx flux in field conditions: the role of blank chambers. Boreal Env. Res. 8: 445–455.

We monitored NOx fluxes in an empty chamber and in chambers containing Scots pine shoots. Our aims were to observe how the chamber blank behaves in non-controlled field conditions and at low ambient NOx concentrations, to find ways of reducing deleterious wall effects, and to evolve a method for a blank correction. We found that solar ultraviolet radiation induced NOx emission from the chamber walls. Comparisons between blanks of several chambers showed that the chambers were not identical. We therefore recommend that a separate blank chamber will be monitored together with the branch chambers in long-term field measurements. At regular time intervals, all of the chambers should be measured simultaneously while empty and the regression between the UV irradiance and NOx flux determined for each chamber. In case the chambers differ from each other, the blank could be corrected with the UV-regression coefficients obtained.
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Sevanto, S., Mikkelsen, T. N., Pilegaard, K. & Vesala, T. 2003: Comparison of tree stem diameter variations in beech (Fagus sylvatica L.) in Sorø Denmark and in Scots pine (Pinus sylvestris L.) in Hyytiälä, Finland. Boreal Env. Res. 8: 457–464.

Tree stem diameter variations were measured simultaneously in beech (Fagus sylvatica L.) in Sorø, Denmark and in Scots pine (Pinus sylvestris L.) in Hyytiälä, Finland. The variations were detected at two heights on the xylem and the whole stem on both trees. The evapo-transpiration of the forests was measured by eddy-covariance method. The pattern of evapo-transpiration was reflected on the diameter variations in both cases. However, the pattern was clearer in Scots pine than in beech. The amplitude of the variation in beech was 0.02 mm in the case of xylem and 0.03 mm in the case of whole stem measurements. In Scots pine the amplitude of xylem diameter variation was 0.05–0.09 mm depending on the measurement height on the xylem and 0.15 mm on the whole stem. The difference in the elasticity of the wood of the two species was reflected in the amplitudes of the variations. The environmental conditions during the measurement period and the measurement methods were similar at both sites, which made the simple comparison possible.
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