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Long-term measurements of fluxes of sensible heat ( H), latent heat ( LE) and carbon dioxide ( Fc) were made from December 2005 to August 2006 over an urban landscape in Helsinki, Finland using the direct micrometeorological eddy covariance technique. Three distinguished sectors of land-use cover (vegetation, roads and buildings) allowed comparisons of fluxes over different urban surfaces. The normalized standard deviation of wind and scalars as a function of atmospheric stability were typical for rough surfaces, as were turbulence spectra and cospectra. Footprint analysis was performed by a boundary-layer one and half-order closure model allowing for discrimination of surface and canopy sinks/sources and complex topography. Fluxes were analysed as average diurnal courses over winter, spring and summer periods. H exceeded LE reaching 300 W m–2 over urban and road surfaces in the summer and it was close to 100 W m–2 in the winter. LE was highest in the summer over vegetation cover attaining 150 W m–2. The emission rate of CO2 was high over road sector [20 μmol (m2s)–1][Correction added after online publication 16 Oct 2007: 30 μmol changed to 20 μmol] while in the vegetation sector it remained below 5 μmol (m2s)–1 and at summertime reached even −10 μmol(m2 s)−1[Correction added after online publication 16 Oct 2007: wording of sentence altered]. Effluxes from soil measured by chambers were 1–3 μmol (m2s)−1. Fc correlated with traffic density and a background non-vehicle flux was 1 μmol (m2s)−1[Correction added after online publication 16 Oct 2007: 2 μmol changed to 1 μmol]. [ABSTRACT FROM AUTHOR]

Eddy covariance (EC) measurements of net ecosystem CO2 exchange (NEE) were conducted on a boreal sedge fen in southern Finland (61°50′N, 24°12′E) during a 1.5-yr period covering two summers in 2004–2005. The EC data were complemented by chamber measurements, which enabled the partition of the daytime NEE into respiration and photosynthesis. A special emphasis was put on the hydrometeorological responses of CO2 exchange during a drought period in July 2005. A mean CO2 efflux of 0.009 mgCO2 m−2 s−1 was observed during mid-winter (January–February), while the night-time respiration during the two Julys averaged 0.09 mgCO2 m−2 s−1. During both years the mean mid-day uptake in late July was about −0.16 mgCO2 m−2 s−1. An annual CO2 balance of −188 gCO2 m−2 was observed in 2005. A slightly higher net sink of −219 gCO2 m−2 was estimated for 2004. The drought period experienced in July 2005 caused a clear depression in the daily NEE values. From the combined analysis of EC and chamber measurements it was concluded that this was mainly due to increased respiration, but evidence was also found of suppressed photosynthesis due to a high VPD. [ABSTRACT FROM AUTHOR]

Net CO2 exchange measured under well-mixed atmospheric conditions in four different mires in Sweden and Finland were used to analyse which factors were controlling photosynthesis and respiration. The parameters of a light response function showed strong seasonal variations with similar behaviour for all mires. The half-monthly nighttime respiration rates in the central part of the growing season were about two times higher in the southernmost, warmest site, Fäje, as compared to the northernmost, coldest site, Kaamanen. However, Kaamanen had high photosynthesis rates, and this in combination with the long daylight periods in the middle of the summer caused Kaamanen to have the largest net ecosystem exchange (NEE) during the summer period. Fäje that showed the highest productivity had also the highest respiration and therefore, the lowest NEE during summer. Correlation between half-monthly components and different environmental variables showed the highest correlation between the components themselves. Thereafter came temperature except for Fäje where water table depth (WTD) explained most of the variance both for detrended and temperature-normalized components. All sites showed dependencies between WTD and the respective components during drying up periods. Temperature sensitivity was higher for productivity than for respiration indicating that CO2 uptake would increase during global warming. [ABSTRACT FROM AUTHOR]

The northern wetlands are one of the major sources of methane into the atmosphere. We measured annual methane emission from a boreal minerotrophic fen, Siikaneva, by the eddy covariance method. The average wintertime emissions were below 1 mg m−2 h−1, and the summertime emissions about 3.5 mg m−2 h−1. The water table depth did have any clear effect on methane emissions. During most of the year the emission depended on the temperature of peat below the water table. However, during the high and late summer the emission was independent on peat temperature as well. No diurnal cycle of methane flux was found. The total annual emission from the Siikaneva site was 12.6 g m−2. The emissions of the snow free period contributed 91% to the annual emission. The emission pulse during the snow melting period was clearly detectable but of minor importance adding only less than 3% to the annual emission. Over 20% of the carbon assimilated during the year as carbon dioxide was emitted as methane. Thus methane emission is an important component of the carbon balance of the Siikaneva fen. This indicates need of taking methane into account when studying carbon balances of northern fen ecosystems. [ABSTRACT FROM AUTHOR]

The continuous measurements of aerosol particle deposition velocity have been performed from January 2004 to January 2005 using a REA technique with dynamic deadband. We measured aerosol particle deposition velocity in the size range of 10–150 nanometer with 5–10 nanometer steps using differential mobility analyser for sizing. We were able to measure two size classes simultaneously. One size class was changed at one month intervals, another we kept constant at 30 nm to investigate the effect of seasonal and meteorological variation on deposition velocity. We found that the 80–100 nanometer size particles had the lowest deposition velocity, about 0.4 cm s−1. Deposition velocity increased with decreasing or increasing particle diameter from 80–100 nanometer size. We also found that deposition velocity increases as a function of friction velocity. [ABSTRACT FROM AUTHOR]