We present a data set covering three months of carbon dioxide (CO2) and energy fluxes measured by the eddy covariance method over a northern boreal lake that collects waters from a surrounding ...catchment dominated by upland forest and wetlands. The data period comprises more than half of the open-water period of 2013. The 30-min averages of CO2 fluxes ranged from –0.02 to 0.05 mg m–2 s–1. The monthly CO2 balances varied from 20 to 30 g m–2 (emission) between July and September, and decreased in October. A small daytime uptake of CO2, probably caused by the aquatic plants growing near the measurement mast, was observed from July to September. In September, we observed a temporary enhancement of CO2 efflux, which was attributed to both high wind speed and rapid cooling of the water and subsequent water column overturn. This peak was accompanied by a period of high sensible heat flux (SHF) from the water to the atmosphere, which is known to enhance the mixing of the water. The seasonal CO2 flux during the open-water period from the shallow part of the lake was estimated to be 120 g m–2 yr–1, which corresponds to a loss of approximately 25 g m–2 yr–1 from the terrestrial part of the catchment, assuming that the observed lake CO2 emissions result from the decomposition of the imported carbon. At midday, the net energy received by the lake was used mostly to heat the water, and only a minor part of it was converted to SHF and latent heat flux (LHF), with more energy used for the latter. While the SHF showed a clear diurnal cycle with a peak early in the morning and no flux in the afternoon, the diurnal pattern of LHF was more even, with evaporation occurring throughout the day until the freezing of the lake. Our data from this northern lake highlight the importance of thermal water mixing in the air–lake CO2 flux dynamics and imply that this flux constitutes a significant part of the annual catchment-scale carbon budget.
Diurnal and annual variations of CO2, O3, SO2, black carbon and condensation nuclei and their source areas were studied by utilizing air parcel trajectories and tropospheric concentration ...measurements at a boreal GAW site in Pallas, Finland. The average growth trend of CO2 was about 2.5 ppm yr−1 according to a 4‐yr measurement period starting in October 1996. The annual cycle of CO2 showed concentration difference of about 19 ppm between the summer minimum and winter maximum. The diurnal cycle was most pronounced during July and August. The variation between daily minimum and maximum was about 5 ppm. There was a diurnal cycle in aerosol concentrations during spring and summer. Diurnal variation in ozone concentrations was weak. According to trajectory analysis the site was equally affected by continental and marine air masses. During summer the contribution of continental air increased, although the southernmost influences decreased. During daytime in summer the source areas of CO2 were mainly located in the northern parts of the Central Europe, while during winter the sources were more evenly distributed. Ozone showed similar source areas during summer, while during winter, unlike CO2, high concentrations were observed in air arriving from the sea. Sulfur dioxide sources were more northern (Kola peninsula and further east) and CO2 sources west‐weighted in comparison to sources of black carbon. Source areas of black carbon were similar to source areas of aerosols during winter. Aerosol source area distributions showed signs of marine sources during spring and summer.
Although atmospheric 222radon (222Rn) activity concentration measurements are currently performed worldwide, they are being made by many different laboratories and with fundamentally different ...measurement principles, so compatibility issues can limit their utility for regional-to-global applications. Consequently, we conducted a European-wide 222Rn ∕ 222Rn progeny comparison study in order to evaluate the different measurement systems in use, determine potential systematic biases between them, and estimate correction factors that could be applied to harmonize data for their use as a tracer in atmospheric applications. Two compact portable Heidelberg radon monitors (HRM) were moved around to run for at least 1 month at each of the nine European measurement stations included in this comparison. Linear regressions between parallel data sets were calculated, yielding correction factors relative to the HRM ranging from 0.68 to 1.45. A calibration bias between ANSTO (Australian Nuclear Science and Technology Organisation) two-filter radon monitors and the HRM of ANSTO ∕ HRM = 1.11 ± 0.05 was found. Moreover, for the continental stations using one-filter systems that derive atmospheric 222Rn activity concentrations from measured atmospheric progeny activity concentrations, preliminary 214Po ∕ 222Rn disequilibrium values were also estimated. Mean station-specific disequilibrium values between 0.8 at mountain sites (e.g. Schauinsland) and 0.9 at non-mountain sites for sampling heights around 20 to 30 m above ground level were determined. The respective corrections for calibration biases and disequilibrium derived in this study need to be applied to obtain a compatible European atmospheric 222Rn data set for use in quantitative applications, such as regional model intercomparison and validation or trace gas flux estimates with the radon tracer method.
A state-of-the-art inverse model, CarbonTracker Data Assimilation Shell (CTDAS), was used to optimize estimates of methane (CH4) surface fluxes using atmospheric observations of CH4 as a constraint. ...The model consists of the latest version of the TM5 atmospheric chemistry-transport model and an ensemble Kalman filter based data assimilation system. The model was constrained by atmospheric methane surface concentrations, obtained from the World Data Centre for Greenhouse Gases (WDCGG). Prior methane emissions were specified for five sources: biosphere, anthropogenic, fire, termites and ocean, of which biosphere and anthropogenic emissions were optimized. Atmospheric CH4 mole fractions for 2007 from northern Finland calculated from prior and optimized emissions were compared with observations. It was found that the root mean squared errors of the posterior estimates were more than halved. Furthermore, inclusion of NOAA observations of CH4 from weekly discrete air samples collected at Pallas improved agreement between posterior CH4 mole fraction estimates and continuous observations, and resulted in reducing optimized biosphere emissions and their uncertainties in northern Finland.
Landfills are one of the largest sources of methane to the atmosphere, yet their emissions are seldom measured. This results in high uncertainties in national emission estimates. We developed a Flame ...Ionization Detector‐based micrometeorological measurement system and tested it at a large municipal landfill in Finland. The technical characteristics of the system allowed use of the eddy covariance method, enabling emission monitoring at a much lower cost than employing a Tunable Diode Laser instrument, which we used as a reference. Combining methane and carbon dioxide flux measurements we were able to estimate the methane generation rate, gas collection efficiency and oxidation rate in the landfill surface layer. We showed that the oxidation fraction may differ significantly from the default value used in the IPCC emission modelling, and that high emission rates were observed in the active deposition areas of the landfill.
We aimed to assess the feasibility of an affordable instrumentation, based on a non-dispersive infrared analyser, to obtain atmospheric CO2 mole fraction data for background CO2 measurements from a ...flux tower site in southern Finland. The measurement period was November 2006–December 2011. We describe the instrumentation, calibration, measurements and data processing and a comparison between two analysers, inter-comparisons with a flask sampling system and with reference gas cylinders and a comparison with an independent inversion model. The obtained accuracy was better than 0.5 ppm. The inter-comparisons showed discrepancies ranging from –0.3 ppm to 0.06 ppm between the measured and reference data. The comparison between the analyzers showed a 0.1 ± 0.4 ppm difference. The trend and phase of the measured and simulated data agreed generally well and the bias of the simulation was 0.2 ± 3.3 ppm. The study highlighted the importance of quantifying all sources of measurement uncertainty.
The alpha/beta analyser uses five gas flow proportional counters: one alpha, one beta and one background detector above the sample, and one beta and one background detector below the sample. The ...counting efficiencies for 210Bi (beta) and 210Po (alpha) are 75% and 42% respectively. The sample changer unit can handle 25 large-area (up to 240 mm diameter) air filters. All combinations of coincidences and pseudo-coincidences between the given detectors can be pre-selected for analysis, thus permitting identification of 222Rn or 220Rn progeny. In addition to total alpha and beta measurements for monitoring purposes, non-destructive assessment of 212Pb and 210Pb have proved valuable in prolonged studies. Beta/alpha pseudo-coincidence techniques provide a procedure to achieve absolute counting efficiencies for short-lived 222Rn progeny, a procedure which also serves as permanent check on instrument stability.
Nitrous oxide (N
2
O) fluxes were measured fortnightly to monthly with manual chambers in 2004–2008 and hourly with automatic chambers during the snow‐free seasons of 2007 and 2008 in a sedge fen in ...northern Finland. The fluxes were generally low, varying from −45 to 37 µg N
2
O–N m
−2
hour
−1
(negative fluxes indicating uptake of N
2
O from the atmosphere into the soil) and showing large spatial and temporal variation. Slightly higher emissions were observed in winter than in summer. On an annual scale, the fen acted as a N
2
O source. The annual balances showed a clear decreasing trend from 1.1 kg N ha
−1
year
−1
(= 12.2 µg N m
−2
hour
−1
) in 2004 to zero balances in 2007 and 2008. Two potential reasons for the decreasing mean flux were (i) a decreasing atmospheric N deposition during the snow‐free season, and (ii) a rising water‐table level (WTL), which restricts the availability of oxygen in the peat and therefore favours the formation of molecular nitrogen (N
2
) instead of N
2
O by the denitrifying microbes. The measurements conducted with the automatic chambers during the snow‐free season showed a positive exponential relationship between the N
2
O flux and the temperature in 2008, but not in 2007. Similarly, a unimodal relationship with the WTL was found in 2008, with maximum fluxes observed when the WTL was about 4 cm above the fen surface. No diurnal variation in N
2
O fluxes measured by automatic chambers was found. The fluxes measured by the manual or automatic chambers were similar in magnitude, but different in their temporal pattern. The daily N
2
O concentration at a depth of 0.15 m in the peat was always lower than the ambient atmospheric concentration, indicating that at this depth the atmospheric N
2
O was consumed. Together with the observed negative flux rates this suggests that microbial N
2
production is a significant part of the N cycle in this fen.
Deposition velocities (vd) of molecular hydrogen were measured in the northern boreal zone in Pallas. Three separate methods were used to estimate the soil uptake rate. For soil chamber measurements, ...three sites (forest, wetland and above tree line) were selected according to different soil properties. The deposition velocity was calculated with radon tracer method taking advantage of nocturnal radon build-up and hydrogen decrease in the shallow mixing layer above ground. A two dimensional model was used to estimate corresponding night time values for vd and radon exhalation rate. The radon tracer and two-dimensional model results were in the range of 0.18–0.52 mm s–1. All results were obtained for unfrozen soils, and there was no clear temperature dependence related to vd. Soil chamber results were in the range of 0.06–0.52 mm s–1 excluding the wetland site which had negligibly small vd due to water saturation.
Daily aerosol samples have been analysed for 210Pb by the Finnish Meteorological Institute since 1967. The arithmetic and geometric mean concentration values were respectively 282 and 208 µBq.m-3 for ...southern Finland and 237 and 169 µBq.m-3 for northern Finland. The daily concentration values were log-normally distributed. The seasonal variations generally follow the vertical mixing in the lower atmosphere, displaying high concentrations in winter with a low mixing height, and vice versa in summer. Usually the lowest 210Pb air concentrations are associated with westerly winds and the highest concentrations with easterly winds. In northern Finland, however, relatively high concentrations were unexpectedly measured during northwesterly winds. Some of these events were connected with high pressure areas over Scandinavia bringing air masses from the European continent. High winter concentrations were closely connected with a cold North Sea surface. No evident trends pertaining to possible climatic changes are discernible in this 30 year observation series.
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