Emission measurements of biogenic volatile organic compounds in multiple scales

Volatile organic compounds (VOCs) are reactive trace gases abundant in the atmosphere. As strongly reactive constituents they have many impacts on the atmospheric chemistry. To properly understand the processes involved in VOC cycles within the biosphere and atmosphere, we must have comprehensive knowledge on the biogenic and anthropogenic emissions and atmospheric concentrations. In this thesis, the emissions of VOCs were measured in many scales from various Fennoscandian ecosystems, utilizing several methods. First, enclosure method was applied to study the branch scale VOC emission from mountain birch. The measurements were conducted during two successive growing seasons. Significant emissions of sesquiterpenes were observed in the first year but not in the second one. Second, relaxed eddy accumulation (REA) method was used to study the ecosystem scale emissions of light hydrocarbons from a wetland. In addition to methane, the only significant emission was that of isoprene. Isoprene emission potential was found to be about 680 μg m-2 h-1. The REA method was further developed by studying the possible stability dependency of the method. Another ecosystem scale flux measurement method, disjunct eddy accumulation (DEA), was applied to study monoterpene emissions from a timber felling area. The emissions of monoterpenes were very high for a few months after felling, peaking at 5200 μg m−2 h−1. Despite of the short period those emissions seem to be of great importance for the atmospheric VOC burden. Third, profiles of boundary layer concentrations of some biogenic and anthropogenic VOCs were measured using a hot air balloon as a platform. Landscape scale emissions were inferred using the concentration data. Overall, our understanding of the previously poorly known VOC emissions from some Fennoscandian ecosystems was increased. This study highlights the importance to quantify emission hotspots of even marginal ecosystems to get comprehensive understanding for emission inventories and future redictions. The correct choice of measuring methods and experiment setup is essential for reliable field data.Haihtuvat orgaaniset yhdisteet (Volatile Organic Compound, VOC) ovat ilmakehässä esiintyviä reaktiivisia hivenkaasuja. Voimakkaasti reaktiivisina aineina niillä on monia vaikutuksia ilmakehän kemiaan. Ymmärtääksemme kunnolla niiden reaktioita biosfäärissä ja ilmakehässä, meillä on oltava hyvä käsitys niiden lähteistä ja ilmapitoisuuksista. Tässä työssä mitattiin VOC päästöjä erilaisista ekosysteemeistä Fennoskandian alueella käyttäen lukuisia eri menetelmiä. Kammiomenetelmää käytettiin tutkittaessa yksittäisten oksien VOC päästöjä tunturikoivusta. Mittauksia tehtiin kahtena peräkkäisen kasvukautena. Ensimmäisenä tutkimusvuonna havaittiin merkittäviä seskviterpeenipäästöjä, mutta toisena tutkimusvuonna niitä ei enää havaittu. Relaxed Eddy Accumulation (REA) menetelmää käytettiin tutkittaessa kevyiden hiilivetyjen ekosysteemiskaalan päästöjä suolta. Metaanin lisäksi vain isopreenin päästö oli merkittävä. Isopreenin emissiopotentiaali oli noin 680 μg m-2 h-1. REA-menetelmää kehitettiin edelleen tutkimalla sen herkkyyttä ilmakehän stabiiliuteen. Toista ekosysteemiskaalan mittausmenetelmää, Disjunct Eddy Accumulation (DEA), käytettiin tutkittaessa monoterpeenipäästöjä hakatusta metsästä. Monoterpeenien päästö oli huomattavan suuri, jopa 5200 μg m-2 h-1, muutaman kuukauden ajan hakkuun jälkeen. Lyhyestä ajanjaksosta huolimatta hakkuualueiden päästöt näyttäisivät olevan merkittäviä ilmakehän monoterpeenikuormitukselle. Useiden biogeenisten ja antropogeenisten VOC-yhdisteiden pitoisuuksien pystygradientteja mitattiin ilmakehän rajakerroksessa käyttäen kuumailmapalloa mittausalustana. Laajan skaalan päästöjä arvioitiin käyttämällä näitä pitoisuustietoja. Tämän työn myötä tietämyksemme eräiden ennestään heikosti tunnettujen Fennoskandian ekosysteemien VOC-päästöistä parani. Tämä tutkimus korostaa myös voimakkaiden, mutta pienialaisten päästölähteiden tuntemisen tärkeyttä. Luotettavan kenttämittaustiedon saamiseksi oikeiden mittausmenetelmien valinta ja tutkimuksen huolellinen suunnittelu on avainasemassa

Urban nitrous-oxide fluxes measured using the eddy-covariance technique in Helsinki, Finland

Peer reviewe

Carbon dioxide and methane fluxes from different surface types in a created urban wetland

Many wetlands have been drained due to urbanization, agriculture, forestry or other purposes, which has resulted in a loss of their ecosystem services. To protect receiving waters and to achieve services such as flood control and storm water quality mitigation, new wetlands are created in urbanized areas. However, our knowledge of greenhouse gas exchange in newly created wetlands in urban areas is currently limited. In this paper we present measurements carried out at a created urban wetland in Southern Finland in the boreal climate. We conducted measurements of ecosystem CO2 flux and CH4 flux (FCH4) at the created storm water wetland Gateway in Nummela, Vihti, Southern Finland, using the eddy covariance (EC) technique. The measurements were commenced the fourth year after construction and lasted for 1 full year and two subsequent growing seasons. Besides ecosystemscale fluxes measured by the EC tower, the diffusive CO2 and CH4 fluxes from the open-water areas (FwCO(2) and FwCH(4), respectively) were modelled based on measurements of CO2 and CH4 concentration in the water. Fluxes from the vegetated areas were estimated by applying a simple mixing model using the above-mentioned fluxes and the footprintweighted fractional area. The half-hourly footprint-weighted contribution of diffusive fluxes from open water ranged from 0% to 25.5% in 2013. The annual net ecosystem exchange (NEE) of the studied wetland was 8.0 g C-CO2 m(-2) yr(-1), with the 95% confidence interval between 18:9 and 34.9 g C-CO2 m(-2) yr(-1), and FCH4 was 3.9 g C-CH4 m(-2) yr(-1), with the 95% confidence interval between 3.75 and 4.07 g C-CH4 m(-2) yr(-1). The ecosystem sequestered CO2 during summer months (June-August), while the rest of the year it was a CO2 source. CH4 displayed strong seasonal dynamics, higher in summer and lower in winter, with a sporadic emission episode in the end of May 2013. Both CH4 and CO2 fluxes, especially those obtained from vegetated areas, exhibited strong diurnal cycles during summer with synchronized peaks around noon. The annual FwCO(2) was 297.5 g C-CO2 m(-2) yr(-1) and FwCH(4) was 1.73 g C-CH4 m(-2) yr(-1). The peak diffusive CH4 flux was 137.6 nmol C-CH4 m(-2) s(-1), which was synchronized with the FCH4. Overall, during the monitored time period, the established storm water wetland had a climate-warming effect with 0.263 kgCO(2)-eqm(-2) yr(-1) of which 89% was contributed by CH4. The radiative forcing of the open-water areas exceeded that of the vegetation areas (1.194 and 0.111 kgCO(2)-eqm(-2) yr(-1), respectively), which implies that, when considering solely the climate impact of a created wetland over a 100-year horizon, it would be more beneficial to design and establish wetlands with large patches of emergent vegetation and to limit the areas of open water to the minimum necessitated by other desired ecosystem services.Peer reviewe

Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements

Peer reviewe

Comparison between static chamber and tunable diode laser-based eddy covariance techniques for measuring nitrous oxide fluxes from a cotton field

Nitrous oxide (N2O) fluxes from a cotton field in northern China were measured for a year using the static chamber method based on a gas chromatograph (GC) and the eddy covariance (EC) technique based on a tunable diode laser (TDL). The aims were to compare the N2O fluxes obtained from both techniques, assess the uncertainties in the fluxes and evaluate the annual direct emission factors (EFds, i.e. the loss rate of fertilizer nitrogen via N2O emission) using the year-round datasets. During the experimental period, the hourly and daily mean chamber fluxes ranged from 0.6 to 781.8 and from 1.2 to 468.8 g N m−2 h−1, respectively. The simultaneously measured daily mean EC fluxes varied between −10.8 and 912.0 g N m−2 h−1. The EC measurements only provided trustworthy 30-min fluxes during high-emission period (a 20-day period immediately after the irrigation that followed the nitrogen fertilization event). A reliable comparison was confined to the high-emission period and showed that the chamber fluxes were 17–20% lower than the EC fluxes. This difference may implicate the magnitude of systematic underestimation in the fluxes from chamber measurements. The annual emission from the fertilized cotton field was estimated at 1.43 kg N ha−1 yr−1 by the chamber observations and 3.15 kg N ha−1 yr−1 by the EC measurements. The EFds calculated from the chamber and EC data were 1.04% and 1.65%, respectively. The chamber-based estimate was very close to the default value (1.0%) recommended by the Intergovernmental Panel on Climate Change. However, the difference in the EFds based on the two measurement techniques may vary greatly with changing environmental conditions and management practices. Further comparison studies are still needed to elucidate this issue.Peer reviewe

Is forest management a significant source of monoterpenes into the boreal atmosphere?

Peer reviewe

Measurements of hydrocarbon emissions from a boreal fen using the REA technique

Fluxes of biogenic volatile organic compounds (VOC) and methane were measured above a boreal fen. Vegetation on the fen is dominated by Sphagnum mosses and sedges. A relaxed eddy accumulation (REA) system with dynamic deadband was designed and constructed for the measurements. Methane, C-2-C-6 hydrocarbons and some halogenated hydrocarbons were analysed from the samples by gas chromatographs equipped with FID and ECD. A significant flux of isoprene and methane was detected during the growing seasons. Isoprene emission was found to follow the common isoprene emission algorithm. Average standard emission potential of isoprene was 680 mu g m(-2) h(-1). Fluxes of other non-methane hydrocarbons were below detection limit.Fluxes of biogenic volatile organic compounds (VOC) and methane were measured above a boreal fen. Vegetation on the fen is dominated by Sphagnum mosses and sedges. A relaxed eddy accumulation (REA) system with dynamic deadband was designed and constructed for the measurements. Methane, C-2-C-6 hydrocarbons and some halogenated hydrocarbons were analysed from the samples by gas chromatographs equipped with FID and ECD. A significant flux of isoprene and methane was detected during the growing seasons. Isoprene emission was found to follow the common isoprene emission algorithm. Average standard emission potential of isoprene was 680 mu g m(-2) h(-1). Fluxes of other non-methane hydrocarbons were below detection limit.Fluxes of biogenic volatile organic compounds (VOC) and methane were measured above a boreal fen. Vegetation on the fen is dominated by Sphagnum mosses and sedges. A relaxed eddy accumulation (REA) system with dynamic deadband was designed and constructed for the measurements. Methane, C-2-C-6 hydrocarbons and some halogenated hydrocarbons were analysed from the samples by gas chromatographs equipped with FID and ECD. A significant flux of isoprene and methane was detected during the growing seasons. Isoprene emission was found to follow the common isoprene emission algorithm. Average standard emission potential of isoprene was 680 mu g m(-2) h(-1). Fluxes of other non-methane hydrocarbons were below detection limit.Peer reviewe

Mountain birch : potentially large source of sesquiterpenes into high latitude atmosphere

Emissions of volatile organic compounds (VOCs) from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up the majority of the tree biomass in Scandinavian high latitudes, a region subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of four branches, each from a different individual tree, were measured in June-August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of the sesquiterpene emission changed dramatically between the years. For example, the average alpha-farnesene emission potential in 2006 was almost 2600 ng g(dw)(-1) h(-1) (3.5 pmol g(dw)(-1) s(-1)) while in 2007 alpha-farnesene was not detected at all. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of alpha-farnesene, and the effect may last for several years.Emissions of volatile organic compounds (VOCs) from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up the majority of the tree biomass in Scandinavian high latitudes, a region subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of four branches, each from a different individual tree, were measured in June-August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of the sesquiterpene emission changed dramatically between the years. For example, the average alpha-farnesene emission potential in 2006 was almost 2600 ng g(dw)(-1) h(-1) (3.5 pmol g(dw)(-1) s(-1)) while in 2007 alpha-farnesene was not detected at all. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of alpha-farnesene, and the effect may last for several years.Emissions of volatile organic compounds (VOCs) from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up the majority of the tree biomass in Scandinavian high latitudes, a region subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of four branches, each from a different individual tree, were measured in June-August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of the sesquiterpene emission changed dramatically between the years. For example, the average alpha-farnesene emission potential in 2006 was almost 2600 ng g(dw)(-1) h(-1) (3.5 pmol g(dw)(-1) s(-1)) while in 2007 alpha-farnesene was not detected at all. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of alpha-farnesene, and the effect may last for several years.Peer reviewe

Temporal Variation of Ecosystem Scale Methane Emission From a Boreal Fen in Relation to Temperature, Water Table Position, and Carbon Dioxide Fluxes

We have analyzed decade-long methane flux data set from a boreal fen, Siikaneva, together with data on environmental parameters and carbon dioxide exchange. The methane flux showed seasonal cycle but no systematic diel cycle. The highest fluxes were observed in July-August with average value of 73 nmol m(-2) s(-1). Wintertime fluxes were small but positive, with January-March average of 6.7 nmol m(-2) s(-1). Daily average methane emission correlated best with peat temperatures at 20-35 cm depths. The second highest correlation was with gross primary production (GPP). The best correspondence between emission algorithm and measured fluxes was found for a variable-slope generalized linear model (r(2) = 0.89) with peat temperature at 35 cm depth and GPP as explanatory variables, slopes varying between years. The homogeneity of slope approach indicated that seasonal variation explained 79% of the sum of squares variation of daily average methane emission, the interannual variation in explanatory factors 7.0%, functional change 5.3%, and random variation 9.1%. Significant correlation between interannual variability of growing season methane emission and that of GPP indicates that on interannual time scales GPP controls methane emission variability, crucially for development of process-based methane emission models. Annual methane emission ranged from 6.0 to 14 gC m(-2) and was 2.7 +/- 0.4% of annual GPP. Over 10-year period methane emission was 18% of net ecosystem exchange as carbon. The weak relation of methane emission to water table position indicates that space-to-time analogy, used to extrapolate spatial chamber data in time, may not be applicable in seasonal time scales.Peer reviewe