Search

Biogenic volatile organic compounds (BVOCs; e.g. terpenes) are highly reactive compounds typically present at sub-parts-per-billion mole fractions in the air. Due to this, their measurements are challenging and they may suffer losses during sampling, storage and analyses. Even though online measurements of BVOCs are becoming more common, the use of sorbent tubes is expected to continue because they offer greater spatial coverage compared to online measurements, and no infrastructure (e.g. electricity, housing/shelter with stable temperature and humidity, sampling lines) is required for sampling. In this study, the performance of an offline technique for the measurement of BVOCs based on sorbent tube sampling was evaluated. Tested compounds included eight monoterpenes, five sesquiterpenes and five oxygenated BVOCs, which are generally either directly emitted (1,8-cineol, linalool, bornyl acetate) or oxidation products (nopinone and 4-acetyl-1-methylcyclohexene). Two sorbent materials (Tenax TA and Carbopack B) and four tube materials (stainless steel (SS), SilcoNert 1000, glass and glass-coated SS) were used. The laboratory evaluations determined the storage stability, breakthrough volumes, suitable tube materials, recovery from ozone scrubbers and particulate filters, and sampling efficiency. In addition, an intercomparison between two laboratories was conducted. No multibed configurations were tested. Of the sorbent materials Tenax TA showed acceptable results for these BVOCs, while with Carbopack B losses and increases in some compounds were detected. Studied compounds were found to be stable in Tenax TA tubes for at least 1 month at - 20 and at + 20 ∘ C. Breakthrough tests indicated that α - and β -pinene have clearly lower breakthrough volumes in the Tenax TA tubes used (4–7 and 8–26 L, respectively) than other terpenes (> 160 L). SS, SilcoNert 1000 and glass were all shown to be suitable tube materials. Results from Tenax TA sorbent tube sampling agreed with online sampling for most compounds. Heated SS tubes, sodium thiosulfate filters and KI/Cu traps were found to be suitable ozone scrubbers for the studied BVOCs. Tested particle filters had a greater impact on limonene (relative difference < + 7 %) than on α - and β -pinene (relative difference ±2 %). The laboratory intercomparison of α - and β -pinene measurements showed that in general, measured values by the two laboratories were in good agreement with Tenax TA. [ABSTRACT FROM AUTHOR]

Urban air consists of a complex mixture of gaseous and particulate species from anthropogenic and biogenic sources that are further processed in the atmosphere. This study investigated the characteristics and sources of volatile organic compounds (VOCs) and submicron organic aerosol (OA) in a traffic environment in Helsinki, Finland, in late summer. The anthropogenic VOCs (aVOCs; aromatic hydrocarbons) and biogenic VOCs (bVOCs; terpenoids) relevant for secondary-organic-aerosol formation were analyzed with an online gas chromatograph mass spectrometer, whereas the composition and size distribution of submicron particles was measured with a soot particle aerosol mass spectrometer. This study showed that aVOC concentrations were significantly higher than bVOC concentrations in the traffic environment. The largest aVOC concentrations were measured for toluene (campaign average of 1630 ng m -3) and p/m xylene (campaign average of 1070 ng m -3), while the dominating bVOC was α -pinene (campaign average of 200 ng m -3). For particle-phase organics, the campaign-average OA concentration was 2.4 µ g m -3. The source apportionment analysis extracted six factors for OA. Three OA factors were related to primary OA sources – traffic (24 % of OA, two OA types) and a coffee roastery (7 % of OA) – whereas the largest fraction of OA (69 %) consisted of oxygenated OA (OOA). OOA was divided into less oxidized semi-volatile OA (SV-OOA; 40 % of OA) and two types of low-volatility OA (LV-OOA; 30 %). The focus of this research was also on the oxidation potential of the measured VOCs and the association between VOCs and OA in ambient air. Production rates of the oxidized compounds (OxPR) from the VOC reactions revealed that the main local sources of the oxidation products were O3 oxidation of bVOCs (66 % of total OxPR) and OH radical oxidation of aVOCs and bVOCs (25 % of total OxPR). Overall, aVOCs produced a much smaller portion of the oxidation products (18 %) than bVOCs (82 %). In terms of OA factors, SV-OOA was likely to originate from biogenic sources since it correlated with an oxidation product of monoterpene, nopinone. LV-OOA consisted of highly oxygenated long-range or regionally transported OA that had no correlation with local oxidant concentrations as it had already spent several days in the atmosphere before reaching the measurement site. In general, the main sources were different for VOCs and OA in the traffic environment. Vehicle emissions impacted both VOC and OA concentrations. Due to the specific VOCs attributed to biogenic emissions, the influence of biogenic emissions was more clearly detected in the VOC concentrations than in OA. In contrast, the emissions from the local coffee roastery had a distinctive mass spectrum for OA, but they could not be seen in the VOC measurements due to the measurement limitations for the large VOC compounds. Long-range transport increased the OA concentration and oxidation state considerably, while its effect was observed less clearly in the VOC measurements due to the oxidation of most VOC in the atmosphere during the transport. Overall, this study revealed that in order to properly characterize the impact of different emission sources on air quality, health, and climate, it is of importance to describe both gaseous and particulate emissions and understand how they interact as well as their phase transfers in the atmosphere during the aging process. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) are ever-present compounds in the air we breathe. They are emitted by natural and anthropogenic sources and are modified by atmospheric oxidants. VOCs affect air quality and human health, form and grow aerosol particles, and can impact Earth's radiative balance. Total hydroxyl radical (OH) reactivity measurements are a valuable tool for assessing the comprehensiveness of measured VOCs and can give valuable insights into in situ atmospheric chemistry. Especially in remote forested environments, missing or unaccounted for reactivity has been substantial, caused by either unmeasured primary emissions or secondary oxidation products. This study presents OH reactivity and VOC measurements over a Nordic, subarctic wetland in summer. Over half of the OH reactivity from emissions could not be attributed, while the remaining measured fraction is dominated by isoprene (42%), followed by sesquiterpenes (3%). [ABSTRACT FROM AUTHOR]

Urban air consists of a complex mixture of gaseous and particulate species from anthropogenic and biogenic sources that are further processed in the atmosphere. This study investigated the features and sources of volatile organic compounds (VOCs) and submicron organic aerosol (OA) at a street canyon in Helsinki, Finland in late summer. The main anthropogenic VOCs (aVOCs) and biogenic VOCs (bVOCs) were analyzed with an online gas chromatograph mass spectrometer, whereas the composition and size distribution of submicron particles was measured with a soot particle aerosol mass spectrometer. This study showed that aVOC concentrations were significantly higher than bVOC concentrations at the street canyon. The largest aVOC concentrations were measured for toluene (campaign-average 1630 ng m-3) and p/m xylene (campaign-average 1070 ng m-3), while the dominating bVOCs was α-pinene (campaign-average 200 ng m-3). The special focus of this research was also on the oxidation of VOCs and the association between VOCs and OA in ambient air. Production rates of the oxidized compounds (OxPR) from the VOC reactions revealed that the main local sources of the oxidation products were O3 oxidation of bVOCs (66 % of total OxPR) and OH radical oxidation of aVOCs and bVOCs (25 % of total OxPR). Overall, aVOCs produced much smaller portion of the oxidation products (18 %) than bVOCs (82 %). For particle phase organics, the source apportionment analysis extracted six factors for OA. Three OA factors were related to primary OA sources, traffic (24 % of OA, two OA types) and coffee roastery (7 % of OA), whereas the largest fraction of OA (69 %) consisted of oxygenated OA (OOA). OOA was divided into less oxidized semi-volatile OA (SV-OOA; 40 % of OA) and two types of low-volatility OA (LV-OOA; 30 %). SV-OOA was likely to originate from biogenic sources since it correlated with an oxidation product of monoterpene, nopinone. LV-OOA consisted of highly oxygenated long-range or regionally transported OA that had no correlation with local oxidant concentrations as it had already spent several days in the atmosphere before reaching the measurement site. By investigating specific air quality cases, it was noticed that the influence of main pollutant sources was different for VOCs and OA at the street canyon. Vehicle emissions impacted both VOC and OA concentrations, whereas the influence of biogenic emissions was more clearly detected in the VOC concentrations than in OA due to the specific VOCs attributed to biogenic emissions. In contrast, the emissions from the local coffee roastery had a distinctive mass spectrum for OA but they could not be seen in the VOC measurements due to the measurement limitations for the large VOC compounds. Long-range transport increased the OA concentrations and oxidation state considerably, while its effect was observed less clearly in the VOC measurements due to the oxidation of most VOC in the atmosphere during the transport. Overall, this study revealed that in order to properly characterize the impact of different emission sources to air quality, health and climate, it is of importance to describe both gaseous and particulate emissions and understand how they interact as well as their phase transfers in the atmosphere during the aging process. [ABSTRACT FROM AUTHOR]

The biogenic volatile organic compound (BVOC) emission rates of Norway spruces published vary a lot. In this study we combined published Norway spruce emission rates measured in boreal forests (Meeningen et al., 2017; Bourtsoukidis et al., 2014a, 2014b; Hakola et al., (2003, 2019)) and added our new, unpublished emission data from southern (SF) and northern Finland (NF). Standardized summer monthly mean emission potentials of isoprene vary from below detection limit to 7 µg g-1 (dw) h-1, and monoterpene (MT) and sesquiterpene (SQT) emission potentials 0.01-3 µg g-1 (dw) h-1 and 0.03-2.7 µg g-1 (dw) h-1, respectively. In this study, we found much higher SQT emissions from Norway spruces than measured before and on average SQTs had higher emission potentials than isoprene or MTs. The highest monthly mean SQT emission potential 13.6 µg g-1 (dw) h-1 was observed in September in southern Finland. We found that none of the younger (33-40 years) trees in Hyytiälä, southern Finland, emitted isoprene, while one 50-year-old tree was a strong isoprene emitter. However, this could not be confirmed at other sites since all measured small trees were growing in Hyytiälä, so this could also be due to the same genetic origin. On average, older trees (>80 years) emitted about ten times more isoprene and MTs than younger ones (<80 years), but no clear difference was seen in SQT emissions. SQT emissions can be more related to stress effects. As shown here for Norway spruce, it is possible that the emission factor of SQTs is significantly higher than what is currently used in models, which may have significant effects on the prediction of formation and growht of new particles, since the secondary organic aerosol (SOA) formation potential of SQTs is high and this may have significant effects on the formation and growth of new particles. Due to high secondary organic aerosol (SOA) formation potentials of SQTs the impact on SOA formation and mass could be even higher. [ABSTRACT FROM AUTHOR]

The East African lowland and highland areas consist of water-limited and humid ecosystems. The magnitude and seasonality of biogenic volatile organic compounds (BVOCs) emissions from these functionally contrasting ecosystems are limited due to a scarcity of direct observations. We measured mixing ratios of BVOCs from two contrasting ecosystems, humid highlands with agroforestry and dry lowlands with bushland, grassland, and agriculture mosaics, during both the rainy and dry seasons of 2019 in southern Kenya. We present the diurnal and seasonal characteristics of BVOC mixing ratios and their reactivity, and estimated emission factors (EFs) for certain BVOCs from the African lowland ecosystem based on field measurements. The most abundant BVOCs were isoprene and monoterpenoids (MTs), with isoprene contributing > 70 % of the total BVOC mixing ratio during daytime, while MTs accounted for > 50 % of the total BVOC mixing ratio during nighttime at both sites. The contributions of BVOCs to the local atmospheric chemistry were estimated by calculating the reactivity towards the hydroxyl radical (OH), ozone (O3), and the nitrate radical (NO3). Isoprene and MTs contributed the most to the reactivity of OH and NO3, while sesquiterpenes dominated the contribution of organic compounds to the reactivity of O3. [ABSTRACT FROM AUTHOR]

Even though isoprene and monoterpene (MT) emissions of boreal needle trees have been studied quite intensively, there is less knowledge on the emissions of broadleaved deciduous trees and emissions of larger terpenes and oxygenated volatile organic compounds (OVOCs). Here we studied the downy birch (Betula pubescens The highest emissions were detected during the early growing season, indicating that bud break and early leaf growth are a strong source of these compounds. Sesquiterpenes (SQTs) and oxygenated sesquiterpenes (OSQTs) were the main emitted compounds almost throughout the summer. Mean emissions (averaged over bud break/early/main and late growing season) of SQTs and OSQTs were 5-690 and 46-650 ng gdw Of the SQTs, β-caryophyllene and β-farnesene were the main compounds emitted in 2019, while in 2017 also high, possibly stress-induced emissions, of α-farnesene were detected. The main emitted OSQTs were tentatively identified as 14-hydroxy-β-caryophyllene acetate (M 262 g/mol) and 6-hydroxy-β-caryophyllene (M 220 g/mol). Of the MTs, α-pinene, β-pinene, limonene and sabinene were the most abundant compounds except during the last two days of the measurements in August in 2019, when β-ocimene emissions had the major contribution. In 2017, when the measured tree was suffering from leaf damages possibly due to drought and high chamber temperature, high emissions of GLVs, linalool, α-farnesene and an unidentified SQT were detected. Emission potentials calculated for 30 &176;C had very high variation between seasons and the highest potentials were detected during bud break and early growing season. Emission potentials calculated separately for each measurement day followed the leaf growth and were highest during the most rapid leaf growth. To our knowledge this is the first time when birch emission rates of OSQTs have been quantified. Even with low emissions, these compounds are expected to have strong impacts on the atmospheric chemistry and especially on secondary organic aerosol (SOA) production. [ABSTRACT FROM AUTHOR]

In forested area, a large fraction of total hydroxyl radical (OH) reactivity remain unaccounted for. Very few studies have been looking at total OH reactivity from biogenic emissions and its variations. In the present study, we investigate the total OH reactivity from three common boreal tree species (Scots pine, Norway spruce, and Downy birch), by comparing it with the calculated reactivity from the chemically identified emissions. Total OH reactivity was measured using the Comparative Reactivity Method (CRM), and the chemical composition of the emissions was quantified with two gas chromatographs coupled to mass spectrometers (GC-MSs). Dynamic branch enclosures were used and emissions from one branch of a tree at the time were measured by rotating between them periodically. Results show that birch had the highest values of total OH reactivity of the emissions (TOHRE), while pine had the lowest. The main drivers for the known reactivity of pine and spruce were monoterpenes and sesquiterpenes. For birch, emissions were dominated by sesquiterpenes, even though monoterpenes and GLVs could be found too. However, calculated reactivity values remained low leading to the highest missing fraction of reactivity (>96%), while pine and spruce had similar missing reactivity fractions between 56% and 82% (higher in the spring and decreasing as the summer proceeded). The high average values were driven by low reactivity periods and the fraction of missing reactivity got smaller for pine and spruce when the TOHRE values increased. Important exceptions were identified for periods when the emission profiles changed from terpenes to Green Leaf Volatiles (GLVs), a family of compounds containing a 6 carbon atoms backbone with various functionalities (e.g. alcohols, aldehydes, esters) that indicate that the plant is suffering from stress. Then, very high TOHRE values were measured and the missing fraction remained high. This study found a different trend in the missing OHRE fraction of Norway spruce from spring to autumn compared to one previous study (Nälscher et al., 2013), which indicates that additional studies are required to fully understand the complexity of biogenic reactive emissions. Future studies of boreal trees in situ should be conducted to confirm the findings presented. [ABSTRACT FROM AUTHOR]

We have studied biogenic VOC emissions and their ambient concentrations at a sub-Arctic wetland (Lompolojänkkä, Finland), which is an open, nutrient-rich sedge fen, and a part of the Pallas-Sodankylä Global Atmosphere Watch (GAW) station. Measurements were conducted during the growing season in 2018 using an in situ thermal desorption - gas chromatograph - mass spectrometer (TD-GC-MS). Earlier studies have shown that isoprene is emitted from boreal wetlands and it turned out to be the most abundant compound in the current study also. Monoterpene (MT) emissions were generally less than 10 % of the isoprene emissions, but sesquiterpenes (SQT) emissions were surprisingly high exceeding MT emissions all the time. During early growing season SQT emission rates were about ten times higher than MT emission rates but this difference became smaller as summer proceeded. Isoprene, MT and SQT emissions were dependent on temperature. Isoprene emission rates were also found to be well-correlated with the gross primary production of CO2. Even with the higher emissions from the wetland, ambient air concentrations of isoprene were clearly lower than MT concentrations. This indicates that wetland was not the only source affecting atmospheric concentrations at the site, but surrounding coniferous forests, which are high MT emitters, contribute as well. In May concentrations of SQTs and MTs at Lompolojänkkä were higher than in earlier boreal forest measurements in southern Finland. At that time the snow cover on the ground was melting and soil thawing and VOCs produced under the snow cover, e.g. by microbes and decaying litter, can be released to the air. Daily mean MT concentrations were very highly negatively correlated with daily mean ozone concentrations indicating that vegetation emissions can be a significant chemical sink of ozone at this sub-Arctic area. [ABSTRACT FROM AUTHOR]

Concentrations of terpenoids (isoprene, monoterpenes, sesquiterpenes) and oxygenated volatile organic compounds (OVOCs, i.e. aldehydes, alcohols, acetates and volatile organic acids) were investigated during two years at a boreal forest site in Hyytiälä, Finland, using in situ gas chromatograph-mass spectrometers (GC-MS). Seasonal and diurnal variations of terpenoid and OVOC concentrations as well as their relationship with meteorological factors were studied. Of the studied VOCs, C2-C7 unbranched volatile organic acids (VOAs) were found to have the highest concentrations mainly due to their low reactivity. Of the terpenoids, monoterpenes (MTs) had highest concentrations at the site, but also 7 different highly reactive sesquiterpenes (SQTs) were detected. Monthly and daily mean concentrations of most terpenoids, aldehydes and VOAs were found to be highly dependent on the temperature. Highest exponential correlation with temperature was found for a SQT (β-caryophyllene) in summer. The diurnal variations of the concentrations could be explained by sources, sinks and vertical mixing. Especially the diurnal variations of MT concentrations were strongly affected by vertical mixing. Based on the temperature correlations and mixing layer height simple proxies were developed for estimating MT and SQT concentrations. To estimate the importance of different compound groups and compounds for the local atmospheric chemistry, reactivity with main oxidants (OH, NO3 and O3) and production rates of oxidation products (OxPR) were calculated. MTs dominated OH and NO3 radical chemistry, but SQTs had a major impact on ozone chemistry, even though concentrations of SQT were 30 times lower than MT concentrations. SQTs were the most important also for the production of oxidation products. Since SQTs have high secondary organic aerosol (SOA) yields, results clearly indicate the importance of SQTs for local SOA production. [ABSTRACT FROM AUTHOR]