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Papers by Hannele Hakola

Tama julkaisu on toteutettu osana valtioneuvoston vuoden 2015 selvitys- ja tutkimussuunnitelman t... more Tama julkaisu on toteutettu osana valtioneuvoston vuoden 2015 selvitys- ja tutkimussuunnitelman toimeenpanoa (tietokayttoon.fi).

Atmospheric Environment, 2020

Biogeosciences Discussions, 2011

Atmospheric chemistry in background areas is strongly influenced by natural vegetation. Coniferou... more Atmospheric chemistry in background areas is strongly influenced by natural vegetation. Coniferous forests are known to produce large quantities of volatile vapors, especially terpenes to the surrounding air. These compounds are reactive in the atmosphere, and contribute to the formation and growth of atmospheric new particles. Our aim was to analyze the variability of mono-and sesquiterpene emissions between Scots pine trees, in order to clarify the potential errors caused by using emission data obtained from only a few trees in atmospheric chemistry models. We also aimed at testing if stand history and seed origin has an influence on the chemotypic diversity. The inherited, chemotypic variability in mono-and sesquiterpene emission was studied in a seemingly homogeneous 47-yr-old stand in Southern Finland, where two areas differing in their stand regeneration history could be distinguished. Sampling was conducted in August 2009. Terpene concentrations in the air had been measured at the same site for seven years prior to branch sampling for chemotypes. Two main compounds, α-pinene and ∆ 3-carene formed together 40-97 % of the monoterpene proportions in both the branch emissions and in the air concentrations. The data showed a bimodal distribution in emission composition, in particular in ∆ 3carene emission within the studied population. 10 % of the trees emitted mainly αpinene and no ∆ 3-carene at all, whereas 20 % of the trees where characterized as high ∆ 3-carene emitters (∆ 3-carene forming > 80 % of total emitted monoterpene spectrum). An intermediate group of trees emitted equal amounts of both α-pinene and ∆ 3-carene. The emission pattern of trees at the area established using seeding as the artificial regeneration method differed from the naturally regenerated or planted trees, being mainly high ∆ 3-carene emitters. Some differences were also seen in e.g. camphene and limonene emissions between chemotypes, but sesquiterpene emissions did not differ significantly between trees. The atmospheric concentrations at the site were found to reflect the species and/or chemodiversity rather than the emissions measured from any single tree, and were strongly dominated by α-pinene. We also tested the 10578

The Science of the total environment, 2018

The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term... more The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990-2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables in 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO) and base cations x(Ca+Mg), hydrogen ion (H), inorganic N (NO and NH) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of ...

Atmospheric Chemistry and Physics Discussions, 2009

Atmospheric concentrations of volatile organic compounds (VOCs) vary diurnally, seasonally and an... more Atmospheric concentrations of volatile organic compounds (VOCs) vary diurnally, seasonally and annually. Therefore continuous long-term measurements are needed to properly describe the atmospheric levels of these chemically reactive compounds. We conducted on-line measurements of atmospheric volume mixing ratios of several VOCs in the European boreal region with a proton transfer reaction-mass spectrometer (PTR-MS) over a 15 month period. The measurements lasted from spring 2006 to fall 2007 and were conducted at SMEAR II station in southwestern Finland. The measured compounds included for example methanol, acetone, sum of isoprene and 2methyl-3-buten-2-ol (MBO), monoterpenes and benzene. The VOC mixing ratios were measured inside and above canopy, during every second or third hour. The PTR-MS was calibrated regularly and background signals of VOCs were measured every second or third hour from the zero air and subtracted from the measured volume mixing ratio. In the continuous measurements at moderate VOC mixing ratios we observed that the PTR-MS has to be calibrated and SEM operation voltage checked regularly, at least twice a month to ensure reliable measurements. Of the measured VOCs, methanol and acetone were the most abundant ones, their volume mixing ratio medians were in the order of 1 ppbv. Volume mixing ratios of methanol, acetone, isoprene-MBO and monoterpenes were high during summer and low in winter indicating mostly biogenic or photochemical local or regional origin. Benzene behaved in the opposite way, while seasonal variation of acetaldehyde and methacrolein-methylvinylketone (MACR-MVK) was less profound. Methanol, acetone, isoprene and monoterpene volume mixing ratios had clear diurnal patterns during summers, while the mixing ratios of other VOCs did not exhibit this behavior. During winter we did not observe systematic diurnal cycles in the VOC volume mixing ratios.

Atmospheric Chemistry and Physics, 2014

Biogenic acids were measured in aerosols at the SMEAR II (Station for Measuring Forest Ecosystem-... more Biogenic acids were measured in aerosols at the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations II) station in Finland from June 2010 until October 2011. The analysed organic acids were pinic, pinonic, caric, limonic and caryophyllinic acids from oxidation of α-pinene, β-pinene, limonene, 3-carene and βcaryophyllene, respectively. Due to a lack of authentic standards, the caric, limonic and caryophyllinic acids were synthesised for this study. The mean, median, maximum and minimum concentrations (ng m −3) were as follows: limonic

Atmospheric Chemistry and Physics Discussions, 2014

Biogenic acids were measured from PM 2.5 aerosols at SMEAR II station (Station For Measuring Fore... more Biogenic acids were measured from PM 2.5 aerosols at SMEAR II station (Station For Measuring Forest Ecosystem-Atmosphere Relations) in Finland from June 2010 until October 2011. The measured organic acids were pinic, pinonic, caric, limonic and caryophyllinic acids from oxidation of α-pinene, β-pinene, limonene, ∆3-carene and β-caryophyllene. Due to lack of authentic standards caric, limonic and caryophyllinic acids were synthesized at the Laboratory of Organic Chemistry, University of Helsinki. The highest terpenoic acid concentrations were measured during summer concomitant with the precursor mono-and sesquiterpenes. Of the acids β-caryophyllinic acid had highest concentrations in summer, but during other times of the year pinonic acid was the most abundant. The β-caryophyllinic acid contribution was higher than expected on the basis of emission calculations of precursor compounds and yields in oxidation experiments in smog chambers implicating that β-caryophyllene emissions or β-caryophyllinic acid yields are underestimated. Concentration ratios between terpenoic acids and their precursor were clearly lower in summer than in winter indicating stronger partitioning to the aerosol phase during cold winter season. The βcaryophyllinic and caric acids were correlated with the accumulation mode particle number concentrations.

Dissertationes Forestales, 2012

Terrestrial ecosystems, mainly plants, emit large amounts of volatile organic compounds (VOCs) in... more Terrestrial ecosystems, mainly plants, emit large amounts of volatile organic compounds (VOCs) into the atmosphere. In addition to plants, VOCs also have less-known sources, such as soil. VOCs are a very diverse group of reactive compounds, including terpenoids, alcohols, aldehydes and ketones. Due to their high reactivity, VOCs take part in chemical reactions in the atmosphere and thus also affect Earth's radiation balance. In this study, chamber and snow gradient techniques for measuring boreal soil and forest floor VOC fluxes were developed. Spatial and temporal variability in fluxes was studied with year-round measurements in the field and the sources of boreal soil VOCs in the laboratory with fungal isolates. Determination of the compounds was performed mass spectrometrically. This study reveals that VOCs from soil are emitted by living roots, above-and belowground litter and microbes. The strongest source appears to be litter, in which both plant residuals and decomposers play a role in the emissions. Temperature and moisture are the most critical physical factors driving VOC fluxes. Since the environment in boreal forests undergoes strong seasonal changes, the VOC flux strength of the forest floor varies markedly during the year, being highest in spring and autumn. The high spatial heterogeneity of the forest floor was also clearly visible in VOC fluxes. The fluxes of trace gases (CO 2 , CH 4 and N 2 O) from soil, which are also related to the soil biological activity and physical conditions, did not correlate with the VOC fluxes. Our results show that emissions of VOCs from the boreal forest floor accounts for as much as several tens of percent, depending on the season, of the total forest ecosystem VOC emissions. This can be utilized in air chemistry models, which are almost entirely lacking the below-canopy compartment.

TemaNord, 2010

to some extent unknown and general predictions of the magnitude of the changes are thus associate... more to some extent unknown and general predictions of the magnitude of the changes are thus associated with a large degree of uncertainty.

Continuous measurements of total gaseous mercury (TGM) at an urban background station in Helsinki... more Continuous measurements of total gaseous mercury (TGM) at an urban background station in Helsinki, Finland, were performed in 2006-2007. Additionally, a one-month campaign to measure TGM continuously from a moving car was organized in 2007, when several cities and industrial areas around Finland were surveyed. In Helsinki, a one-year average of 1.54 ± 0.20 ng m-3 was measured, which is about the global average for this persistent pollutant. The highest concentrations, up to 2500 ng m-3 , were measured during firing practice that took place next to the station. Seasonal and diurnal variation was studied, and trajectory maps were constructed to analyze mercury source regions. In the mobile measurement campaign, concentrations varying between 1.0 and 13.8 ng m-3 were measured. The highest concentrations (above 10 ng m-3) were recorded close to former chlor-alkali plants that used mercury in their electrolytic production process.

We measured volatile organic compound (VOC) volume mixing ratios (VMRs) using a quadrupole proton... more 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.

Current Opinion in Environmental Sustainability, 2013

Biogeosciences, 2012

Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in bore... more Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in boreal forests these fluxes and their seasonal variations have not been characterized in detail. Especially wintertime fluxes are almost completely unstudied. In this study, we measured the VOC concentrations inside the snowpack in a boreal Scots pine (Pinus sylvestris L.) forest in southern Finland, using adsorbent tubes and air samplers installed permanently in the snow profile. Based on the VOC concentrations at three heights inside the snowpack, we estimated the fluxes of these gases. We measured 20 VOCs from the snowpack, monoterpenes being the most abundant group with concentrations varying from 0.11 to 16 µg m −3. Sesquiterpenes and oxygencontaining monoterpenes were also detected. Inside the pristine snowpack, the concentrations of terpenoids decreased from soil surface towards the surface of the snow, suggesting soil as the source for terpenoids. Forest damages (i.e. broken treetops and branches, fallen trees) resulting from heavy snow loading during the measurement period increased the terpenoid concentrations dramatically, especially in the upper part of the snowpack. The results show that soil processes are active and efficient VOC sources also during winter, and that natural or human disturbance can increase forest floor VOC concentrations substantially. Our results stress the importance of soil as a source of VOCs during the season when other biological sources, such as plants, have lower activity.

Biogeosciences, 2012

Volatile organic compounds (VOCs) including terpenoids are emitted into the atmosphere from vario... more Volatile organic compounds (VOCs) including terpenoids are emitted into the atmosphere from various natural sources. Damaging the plant tissue is known to strongly increase their monoterpene release. We measured the terpenoid emissions caused by timber felling, i.e. those from stumps and logging residue. The emissions from stumps were studied using enclosures and those from the whole felling area using an ecosystem-scale micrometeorological method, disjunct eddy accumulation (DEA). The compounds analyzed were isoprene, monoterpenes and sesquiterpenes. Strong emissions of monoterpenes were measured from both the stumps and from the whole felling area. The emission rate decreased rapidly within a few months after the logging. In addition to fresh logging residue, the results suggest also other strong monoterpene sources may be present in the felling area. These could include pre-existing litter, increased microbial activity and remaining undergrowth. In order to evaluate the possible importance of monoterpenes emitted annually from cut Scots pine forests in Finland, we conducted a rough upscaling calculation. The resulting monoterpene release was approximated to be on the order of 15 kilotonnes per year, which corresponds to about one tenth of the monoterpene release from intact forests in Finland.

Biogeosciences, 2009

Emissions of volatile organic compounds (VOCs) from mountain birches were measured in Abisko, nor... more 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 α-farnesene emission potential in 2006 was almost 2600 ng g −1 dw h −1 (3.5 pmol g −1 dw s −1) while in 2007 αfarnesene 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 α-farnesene, and the effect may last for several years.

Atmospheric Environment, 2011

Polycyclic aromatic hydrocarbons (PAH compounds) were measured in the PM 10 fraction [from ambien... more Polycyclic aromatic hydrocarbons (PAH compounds) were measured in the PM 10 fraction [from ambient air] at Virolahti, Finland. The sampling site is located in a rural area in the southeastern corner of Finland, near the Russian border. Altogether, 51 daily and 85 weekly filter samples were collected in 2007e2008. The yearly average concentration of benzo(a)pyrene at Virolahti in 2007 was 0.21 ng m À3 , which is well below the annual target value of 1 ng m À3 set by the European Union. The positive matrix factorization (PMF) method was applied in source apportionment for daily PAH data combined with other pollutant data. A three-factor solution of the PMF analysis with 28 components was chosen. These three factors were identified as long-range transported secondary particles (F1), combustion (F2) and a sea-salt factor (F3). The conditional probability function (CPF) was used to combine wind direction sectors with the PMF factors. In cases F1 and F2, pollutants mainly originated from the southeast , whereas pollutants in F3 came from the southwestern sector. PAHs entered into the combustion factor 2 together with SO 2 , NO x , black carbon and potassium. This suggests that the PAHs at Virolahti originated from traffic and industrial pollution, as well as biomass burning. Elevated concentrations occurred throughout the winter period and most frequently originated from the southeastern sector between 90 e135. This sector includes, among other transboundary areas, the metropolis of St. Petersburg at a distance of 160 km.

Atmospheric Environment, 2008

In the spring and summer of 2006 the air quality in southern Finland was affected by two major bi... more In the spring and summer of 2006 the air quality in southern Finland was affected by two major biomass fire smoke episodes. At the Virolahti background station, closest to the eastern fire areas, the episodes lasted altogether several weeks. The high point in spring was 25 April and in summer 13 August. In spring the aerosol detected at Virolahti originated

Atmospheric Environment, 2005

Tama julkaisu on toteutettu osana valtioneuvoston vuoden 2015 selvitys- ja tutkimussuunnitelman t... more Tama julkaisu on toteutettu osana valtioneuvoston vuoden 2015 selvitys- ja tutkimussuunnitelman toimeenpanoa (tietokayttoon.fi).

Atmospheric Environment, 2020

Biogeosciences Discussions, 2011

Atmospheric chemistry in background areas is strongly influenced by natural vegetation. Coniferou... more Atmospheric chemistry in background areas is strongly influenced by natural vegetation. Coniferous forests are known to produce large quantities of volatile vapors, especially terpenes to the surrounding air. These compounds are reactive in the atmosphere, and contribute to the formation and growth of atmospheric new particles. Our aim was to analyze the variability of mono-and sesquiterpene emissions between Scots pine trees, in order to clarify the potential errors caused by using emission data obtained from only a few trees in atmospheric chemistry models. We also aimed at testing if stand history and seed origin has an influence on the chemotypic diversity. The inherited, chemotypic variability in mono-and sesquiterpene emission was studied in a seemingly homogeneous 47-yr-old stand in Southern Finland, where two areas differing in their stand regeneration history could be distinguished. Sampling was conducted in August 2009. Terpene concentrations in the air had been measured at the same site for seven years prior to branch sampling for chemotypes. Two main compounds, α-pinene and ∆ 3-carene formed together 40-97 % of the monoterpene proportions in both the branch emissions and in the air concentrations. The data showed a bimodal distribution in emission composition, in particular in ∆ 3carene emission within the studied population. 10 % of the trees emitted mainly αpinene and no ∆ 3-carene at all, whereas 20 % of the trees where characterized as high ∆ 3-carene emitters (∆ 3-carene forming > 80 % of total emitted monoterpene spectrum). An intermediate group of trees emitted equal amounts of both α-pinene and ∆ 3-carene. The emission pattern of trees at the area established using seeding as the artificial regeneration method differed from the naturally regenerated or planted trees, being mainly high ∆ 3-carene emitters. Some differences were also seen in e.g. camphene and limonene emissions between chemotypes, but sesquiterpene emissions did not differ significantly between trees. The atmospheric concentrations at the site were found to reflect the species and/or chemodiversity rather than the emissions measured from any single tree, and were strongly dominated by α-pinene. We also tested the 10578

The Science of the total environment, 2018

The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term... more The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990-2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables in 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO) and base cations x(Ca+Mg), hydrogen ion (H), inorganic N (NO and NH) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of ...

Atmospheric Chemistry and Physics Discussions, 2009

Atmospheric concentrations of volatile organic compounds (VOCs) vary diurnally, seasonally and an... more Atmospheric concentrations of volatile organic compounds (VOCs) vary diurnally, seasonally and annually. Therefore continuous long-term measurements are needed to properly describe the atmospheric levels of these chemically reactive compounds. We conducted on-line measurements of atmospheric volume mixing ratios of several VOCs in the European boreal region with a proton transfer reaction-mass spectrometer (PTR-MS) over a 15 month period. The measurements lasted from spring 2006 to fall 2007 and were conducted at SMEAR II station in southwestern Finland. The measured compounds included for example methanol, acetone, sum of isoprene and 2methyl-3-buten-2-ol (MBO), monoterpenes and benzene. The VOC mixing ratios were measured inside and above canopy, during every second or third hour. The PTR-MS was calibrated regularly and background signals of VOCs were measured every second or third hour from the zero air and subtracted from the measured volume mixing ratio. In the continuous measurements at moderate VOC mixing ratios we observed that the PTR-MS has to be calibrated and SEM operation voltage checked regularly, at least twice a month to ensure reliable measurements. Of the measured VOCs, methanol and acetone were the most abundant ones, their volume mixing ratio medians were in the order of 1 ppbv. Volume mixing ratios of methanol, acetone, isoprene-MBO and monoterpenes were high during summer and low in winter indicating mostly biogenic or photochemical local or regional origin. Benzene behaved in the opposite way, while seasonal variation of acetaldehyde and methacrolein-methylvinylketone (MACR-MVK) was less profound. Methanol, acetone, isoprene and monoterpene volume mixing ratios had clear diurnal patterns during summers, while the mixing ratios of other VOCs did not exhibit this behavior. During winter we did not observe systematic diurnal cycles in the VOC volume mixing ratios.

Atmospheric Chemistry and Physics, 2014

Biogenic acids were measured in aerosols at the SMEAR II (Station for Measuring Forest Ecosystem-... more Biogenic acids were measured in aerosols at the SMEAR II (Station for Measuring Forest Ecosystem-Atmosphere Relations II) station in Finland from June 2010 until October 2011. The analysed organic acids were pinic, pinonic, caric, limonic and caryophyllinic acids from oxidation of α-pinene, β-pinene, limonene, 3-carene and βcaryophyllene, respectively. Due to a lack of authentic standards, the caric, limonic and caryophyllinic acids were synthesised for this study. The mean, median, maximum and minimum concentrations (ng m −3) were as follows: limonic

Atmospheric Chemistry and Physics Discussions, 2014

Biogenic acids were measured from PM 2.5 aerosols at SMEAR II station (Station For Measuring Fore... more Biogenic acids were measured from PM 2.5 aerosols at SMEAR II station (Station For Measuring Forest Ecosystem-Atmosphere Relations) in Finland from June 2010 until October 2011. The measured organic acids were pinic, pinonic, caric, limonic and caryophyllinic acids from oxidation of α-pinene, β-pinene, limonene, ∆3-carene and β-caryophyllene. Due to lack of authentic standards caric, limonic and caryophyllinic acids were synthesized at the Laboratory of Organic Chemistry, University of Helsinki. The highest terpenoic acid concentrations were measured during summer concomitant with the precursor mono-and sesquiterpenes. Of the acids β-caryophyllinic acid had highest concentrations in summer, but during other times of the year pinonic acid was the most abundant. The β-caryophyllinic acid contribution was higher than expected on the basis of emission calculations of precursor compounds and yields in oxidation experiments in smog chambers implicating that β-caryophyllene emissions or β-caryophyllinic acid yields are underestimated. Concentration ratios between terpenoic acids and their precursor were clearly lower in summer than in winter indicating stronger partitioning to the aerosol phase during cold winter season. The βcaryophyllinic and caric acids were correlated with the accumulation mode particle number concentrations.

Dissertationes Forestales, 2012

Terrestrial ecosystems, mainly plants, emit large amounts of volatile organic compounds (VOCs) in... more Terrestrial ecosystems, mainly plants, emit large amounts of volatile organic compounds (VOCs) into the atmosphere. In addition to plants, VOCs also have less-known sources, such as soil. VOCs are a very diverse group of reactive compounds, including terpenoids, alcohols, aldehydes and ketones. Due to their high reactivity, VOCs take part in chemical reactions in the atmosphere and thus also affect Earth's radiation balance. In this study, chamber and snow gradient techniques for measuring boreal soil and forest floor VOC fluxes were developed. Spatial and temporal variability in fluxes was studied with year-round measurements in the field and the sources of boreal soil VOCs in the laboratory with fungal isolates. Determination of the compounds was performed mass spectrometrically. This study reveals that VOCs from soil are emitted by living roots, above-and belowground litter and microbes. The strongest source appears to be litter, in which both plant residuals and decomposers play a role in the emissions. Temperature and moisture are the most critical physical factors driving VOC fluxes. Since the environment in boreal forests undergoes strong seasonal changes, the VOC flux strength of the forest floor varies markedly during the year, being highest in spring and autumn. The high spatial heterogeneity of the forest floor was also clearly visible in VOC fluxes. The fluxes of trace gases (CO 2 , CH 4 and N 2 O) from soil, which are also related to the soil biological activity and physical conditions, did not correlate with the VOC fluxes. Our results show that emissions of VOCs from the boreal forest floor accounts for as much as several tens of percent, depending on the season, of the total forest ecosystem VOC emissions. This can be utilized in air chemistry models, which are almost entirely lacking the below-canopy compartment.

TemaNord, 2010

to some extent unknown and general predictions of the magnitude of the changes are thus associate... more to some extent unknown and general predictions of the magnitude of the changes are thus associated with a large degree of uncertainty.

Continuous measurements of total gaseous mercury (TGM) at an urban background station in Helsinki... more Continuous measurements of total gaseous mercury (TGM) at an urban background station in Helsinki, Finland, were performed in 2006-2007. Additionally, a one-month campaign to measure TGM continuously from a moving car was organized in 2007, when several cities and industrial areas around Finland were surveyed. In Helsinki, a one-year average of 1.54 ± 0.20 ng m-3 was measured, which is about the global average for this persistent pollutant. The highest concentrations, up to 2500 ng m-3 , were measured during firing practice that took place next to the station. Seasonal and diurnal variation was studied, and trajectory maps were constructed to analyze mercury source regions. In the mobile measurement campaign, concentrations varying between 1.0 and 13.8 ng m-3 were measured. The highest concentrations (above 10 ng m-3) were recorded close to former chlor-alkali plants that used mercury in their electrolytic production process.

We measured volatile organic compound (VOC) volume mixing ratios (VMRs) using a quadrupole proton... more 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.

Current Opinion in Environmental Sustainability, 2013

Biogeosciences, 2012

Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in bore... more Soil provides an important source of volatile organic compounds (VOCs) to atmosphere, but in boreal forests these fluxes and their seasonal variations have not been characterized in detail. Especially wintertime fluxes are almost completely unstudied. In this study, we measured the VOC concentrations inside the snowpack in a boreal Scots pine (Pinus sylvestris L.) forest in southern Finland, using adsorbent tubes and air samplers installed permanently in the snow profile. Based on the VOC concentrations at three heights inside the snowpack, we estimated the fluxes of these gases. We measured 20 VOCs from the snowpack, monoterpenes being the most abundant group with concentrations varying from 0.11 to 16 µg m −3. Sesquiterpenes and oxygencontaining monoterpenes were also detected. Inside the pristine snowpack, the concentrations of terpenoids decreased from soil surface towards the surface of the snow, suggesting soil as the source for terpenoids. Forest damages (i.e. broken treetops and branches, fallen trees) resulting from heavy snow loading during the measurement period increased the terpenoid concentrations dramatically, especially in the upper part of the snowpack. The results show that soil processes are active and efficient VOC sources also during winter, and that natural or human disturbance can increase forest floor VOC concentrations substantially. Our results stress the importance of soil as a source of VOCs during the season when other biological sources, such as plants, have lower activity.

Biogeosciences, 2012

Volatile organic compounds (VOCs) including terpenoids are emitted into the atmosphere from vario... more Volatile organic compounds (VOCs) including terpenoids are emitted into the atmosphere from various natural sources. Damaging the plant tissue is known to strongly increase their monoterpene release. We measured the terpenoid emissions caused by timber felling, i.e. those from stumps and logging residue. The emissions from stumps were studied using enclosures and those from the whole felling area using an ecosystem-scale micrometeorological method, disjunct eddy accumulation (DEA). The compounds analyzed were isoprene, monoterpenes and sesquiterpenes. Strong emissions of monoterpenes were measured from both the stumps and from the whole felling area. The emission rate decreased rapidly within a few months after the logging. In addition to fresh logging residue, the results suggest also other strong monoterpene sources may be present in the felling area. These could include pre-existing litter, increased microbial activity and remaining undergrowth. In order to evaluate the possible importance of monoterpenes emitted annually from cut Scots pine forests in Finland, we conducted a rough upscaling calculation. The resulting monoterpene release was approximated to be on the order of 15 kilotonnes per year, which corresponds to about one tenth of the monoterpene release from intact forests in Finland.

Biogeosciences, 2009

Emissions of volatile organic compounds (VOCs) from mountain birches were measured in Abisko, nor... more 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 α-farnesene emission potential in 2006 was almost 2600 ng g −1 dw h −1 (3.5 pmol g −1 dw s −1) while in 2007 αfarnesene 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 α-farnesene, and the effect may last for several years.

Atmospheric Environment, 2011

Polycyclic aromatic hydrocarbons (PAH compounds) were measured in the PM 10 fraction [from ambien... more Polycyclic aromatic hydrocarbons (PAH compounds) were measured in the PM 10 fraction [from ambient air] at Virolahti, Finland. The sampling site is located in a rural area in the southeastern corner of Finland, near the Russian border. Altogether, 51 daily and 85 weekly filter samples were collected in 2007e2008. The yearly average concentration of benzo(a)pyrene at Virolahti in 2007 was 0.21 ng m À3 , which is well below the annual target value of 1 ng m À3 set by the European Union. The positive matrix factorization (PMF) method was applied in source apportionment for daily PAH data combined with other pollutant data. A three-factor solution of the PMF analysis with 28 components was chosen. These three factors were identified as long-range transported secondary particles (F1), combustion (F2) and a sea-salt factor (F3). The conditional probability function (CPF) was used to combine wind direction sectors with the PMF factors. In cases F1 and F2, pollutants mainly originated from the southeast , whereas pollutants in F3 came from the southwestern sector. PAHs entered into the combustion factor 2 together with SO 2 , NO x , black carbon and potassium. This suggests that the PAHs at Virolahti originated from traffic and industrial pollution, as well as biomass burning. Elevated concentrations occurred throughout the winter period and most frequently originated from the southeastern sector between 90 e135. This sector includes, among other transboundary areas, the metropolis of St. Petersburg at a distance of 160 km.

Atmospheric Environment, 2008

In the spring and summer of 2006 the air quality in southern Finland was affected by two major bi... more In the spring and summer of 2006 the air quality in southern Finland was affected by two major biomass fire smoke episodes. At the Virolahti background station, closest to the eastern fire areas, the episodes lasted altogether several weeks. The high point in spring was 25 April and in summer 13 August. In spring the aerosol detected at Virolahti originated

Atmospheric Environment, 2005