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Long-term, continuous observations are needed for Earth system investigations and evaluation of simulations. The atmospheric and ecological communities have independently established field sites that have been running for many decades and are integrated into global networks. In the past decade, the importance of long-term observational networks focused on land ecosystem-atmosphere exchange, and the processes controlling land-atmosphere coupling, had been increasingly recognized and has led to the building of a global network of water, carbon and energy flux sites. This is an important step but further enhancements are necessary in order to quantify all of the land-atmosphere processes that need to be included in Earth system models. This paper describes the current land ecosystem-atmosphere measurement capabilities and presents the status and needs for global observational networks.

The subject of the study was the effect of monoterpene oxidation on the growth of particles during new-particle formation (NPF) events at the SMEAR II measurement station in Hyytiälä, southern Finland, during 2006-2011. The nighttime oxidation capacity, i.e. how readily the atmosphere can oxidize monoterpenes, was found to be dominated by the nitrate radical, whereas the daytime oxidation capacity was mainly dominated by ozone. The mean lifetimes of monoterpenes ranged from about one hour to several hours, depending on the time of year and day. A strong link was found between the growth rate of particles of 7-20 nm in diameter during the NPF events and monoterpene oxidation by ozone during the preceding night. Our findings suggest that during nighttime a build-up of primarily oxidized monoterpenes in the atmosphere occurs, and that these compounds can be oxidized by the hydroxyl radical after sunrise, promoting the particle growth. [ABSTRACT FROM AUTHOR]

We measured VOC fluxes using disjunct-eddy-covariance (DEC), surface-layer-gradient (SLG), and surface-layer-profile (SLP) methods with proton transfer reaction mass spec-trometry (PTR-MS) above a boreal forest in Hyytiälä, Finland. Our aim was to examine the reliability and feasibility of these methods for long-term measurements at low-flux conditions typical for boreal forests. The compounds targeted were formaldehyde, methanol, acetaldehyde, acetone, isoprene/methylbutenol fragment, methylbutenol, hexanal, hexenal and monoterpenes. We carried out a 10-day comparison between the techniques and used longer continuous data sets for the feasibility study. Out of these surface layer methods, the SLP method performed the best. We found out that with the SLP method we were able to detect fluxes for all the targeted compounds except formaldehyde. The method had also smaller detection limits and better data coverage than the DEC method. The systematic error of both SLP and SLG techniques was estimated to be around 10% for these measurements and it was caused by the high frequency attenuation for the DEC and by the turbulence parametrization for the SLP. As a conclusion the SLP method can be recommend for long-term flux measurements in low-flux conditions. [ABSTRACT FROM AUTHOR]

We measured volatile organic compound (VOC) volume mixing ratios (VMRs) using a quadrupole proton-transfer-reaction mass spectrometer, and investigated the differences between winter and spring VMRs and sources at an urban background site in Helsinki (2006) and a rural site in Hyytiälä (2007) utilizing a receptor model EPA Unmix. In Helsinki, VMRs of VOCs were typically higher,and their diurnal variations were more pronounced than at the rural site. At both sites, monoterpenes have anthropogenic influence in winter, while in spring biogenic influence is dominating. At the urban background site, the main aromatic hydrocarbon source was traffic, which also explained most of the oxidated VOCs during the urban winter. At other times and at the rural location most of oxidated VOCs originated mainly from distant sources. At the rural site, traffic and distant sources contributed equally to the aromatics in winter but in spring the distant source dominated. [ABSTRACT FROM AUTHOR]

We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol. [ABSTRACT FROM AUTHOR]

In this paper, the research conducted on the emissions of the biogenic volatile organic compounds (BVOCs) from the European boreal zone, or taiga, is reviewed. We highlight the main findings and the key gaps in our knowledge. Ecosystem scale BVOC emissions from the Eurasian taiga are observed to be relatively low as compared with those from some forest ecosystems in warmer climates. One of the distinctive features of the Eurasian taiga is the predominance of monoterpene emitting coniferous trees. Recent research indicates that in addition to evaporation from storage structures, part of the monoterpene emission of conifers originates directly from synthesis. Monoterpene emission from boreal deciduous trees originates mainly directly from synthesis. The boreal trees exhibit distinct intra-species variation in the monoterpene mixtures they emit. Important sources of isoprene in the Eurasian taiga include Norway spruce, open wetland ecosystems and some non-dominant woody species, such as European aspen and willows. Many boreal tree species also emit non-terpenoid compounds and highly reactive sesquiterpenes. The future challenges in the research on BVOC emissions from the Eurasian taiga include (i) quantification and understanding the non-terpenoid VOC emissions from the taiga ecosystems, (ii) bringing ecosystems in the eastern Eurasian taiga into the sphere of BVOC emission studies, (iii) establishing long-term ecosystem flux studies combined with plant physiological measurements, and (iv) integrating knowledge and research skills on BVOC synthesis, strorages and emissions, land cover changes and atmospheric processes in different spatial and temporal scales in order to better understand the impact of biosphere on atmospheric chemistry and composition in changing climate. [ABSTRACT FROM AUTHOR]

Ambient atmospheric concentrations of monoterpene compounds were measured above a boreal forest in Hyytiälä, Finland during 2000-2007. For most of the time, two samples per week were collected, although there are some gaps in the data due to analytical or other issues. The monoterpene concentrations reached their maximum in summer, although they were found to be quite high also during winter. The main compounds found during winter were α-pinene, Δ3-carene, β-pinene and camphene. In summer 1,8-cineol and sabinene were also present in the samples. The concentrations of α-pinene, β-pinene/myrcene, camphene, Δ3-carene increased during the measurement period both in winter and in summer. This increase cannot be explained by meteorological conditions. The possible explanations could be human activities in the vicinity of the sampling site in addition to forest growth. The seasonal cycles of daytime concentrations were found to follow emission fluxes modeled using a simple temperature dependent parameterisation. The measured monoterpene concentrations were used, together with emission rate measurements, for estimating ambient atmospheric β-caryophyllene concentration which cannot be directly measured due to its high reactivity against ozone. [ABSTRACT FROM AUTHOR]

We measured the daily patterns of monoterpene emissions from Scots pine (Pinus sylvestris) trees in a boreal coniferous forest in August and September 2004, using an on-line chamber method combined with a proton-transfer-reaction mass spectrometry (PTR-MS) analyzer. The on-line measurements were made in two chambers with a one-year old shoot inside. Simultaneous measurements were performed for carbon dioxide (CO2) exchange, transpiration (H2O), exchange of trace gases (NOx, O3), photosynthetic photon fux density (PPFD), air temperature and relative humidity (RH). The composition of the monoterpene emission did not change during the measurement period, with Δ³-carene and α-pinene being the dominant species. The total monoterpene emission rate (per needle area) was on average 0.5 ng m-2 s-1, varied from non detectable to 2.1 ng m-2 s-1, and showed a typical diurnal pattern with afternoon maximum and nighttime minimum. The emission rates determined with this on-line chamber method were in agreement with results from a simultaneously used established adsorbent sampling technique with offline GC-MS analysis. The monoterpene emissions from the chamber walls were correlated with the chamber temperature and this measurement artifact was dominating at night. Emission rates normalized to 30 °C, using temperature regression coefficient of 0.09 °C-1, ranged from 2.1 μg g(dw)-1 h-1 to 4.4 μg g(dw)-1 h-1. Measurements of emission dynamics of biogenic volatile organic compounds (BVOCs) together with plant physiological activity are urgently needed for the development of mechanistic BVOC emission models in order to assess their regional and global influence. [ABSTRACT FROM AUTHOR]

The eddy covariance method was used to determine turbulent heat fluxes and CO2 flux below a boreal Scots pine canopy 3 m above the forest floor. Data were filtered using standard deviation of the vertical velocity as a measure of the turbulent mixing in the trunk space along with the non-stationary criterion. The turbulent transfer in the trunk space was dominated by large (15–100 m) intermittent eddies, which were detectable by the eddy covariance technique. Heat fluxes exhibited clear annual and diurnal course and amounted to 20%–30% of the fluxes above the canopy. The forest floor was a source of carbon all-year-round and the CO2 efflux was mainly controlled by soil temperature. Photosynthesis of the forest floor vegetation decreased daytime fluxes of CO2 by 1.0–1.5 μmol m-2 s-1 compared with nocturnal values (∼3.0 μmol m-2 s-1). The eddy covariance method provided a similar daily cycle to the chamber method but there was a discrepancy between their mean levels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]