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To estimate the effect of vegetation stress and changes in biogenic volatile organic compound (BVOC) emissions on urban ozone (O3) levels we perform a systematic, observation-based analysis of the relationship between formaldehyde (HCHO) mixing ratios, meteorological parameters, measurement-based drought indicators and O3 over the central European city of Vienna, Austria. In addition, numerical models SURface EXternalisée (SURFEX), Model of Emissions of Gases and Aerosols from Nature (MEGAN) Vers.2.1 and 3 and MOdèle de Chimie A Grande Echelle (MOCAGE) are combined to estimate the soil moisture, the spatial distribution and drought response of isoprene emissions, and the resulting distribution of HCHO in the atmosphere. To analyse the effect of drought during spring and summer we contrast observations during dry and reference years. Our results show that the observed HCHO can be explained using the simulated isoprene emissions as well as observed and simulated vegetation drought responses. HCHO mixing ratios differ strongly between dry and reference seasons. Spring-time precipitation deficits facilitate reduced HCHO mixing ratios due to delayed and weakened plant growth. In consequence also O3 burdens are lowered due to reduced BVOC precursor emissions. These reductions occur despite radiation levels being higher than during the reference year, illustrating the strong potential of spring-time BVOC emissions to modulate urban O3 burdens. Conversely, during summer elevated O3 levels occur during local drought conditions. These are driven by advected isoprene originating from nearby forest areas, which are not affected by drought. Our results regarding elevated summer-time O3 burdens under vegetation heat and drought stress are in good agreement with previous work.

Altres ajuts: acords transformatius de la UAB Unidad de excelencia María de Maeztu CEX2019-000940-M Urban green installations are extensively promoted to increase sustainable and accessible food production and simultaneously improve the environmental performance and liveability of city buildings. In addition to the multiple benefits of plant retrofitting, these installations may lead to a consistent increase in biogenic volatile organic compounds (BVOCs) in the urban environment, especially indoors. Accordingly, health concerns could limit the implementation of building-integrated agriculture. In a building-integrated rooftop greenhouse (i-RTG), throughout the whole hydroponic cycle, green bean emissions were dynamically collected in a static enclosure. Four representative BVOCs, α-pinene (monoterpene), β-caryophyllene (sesquiterpene), linalool (oxygenated monoterpene) and cis-3-hexenol (LOX derivate), were investigated in the samples collected from two equivalent sections of a static enclosure, one empty and one occupied by the i-RTG plants, to estimate the volatile emission factor (EF). Throughout the season, extremely variable BVOC levels between 0.04 and 5.36 ppb were found with occasional but not significant (P > 0.05) variations between the two sections. The highest emission rates were observed during plant vegetative development, with EFs equivalent to 78.97, 75.85 and 51.34 ng g−1 h−1 for cis-3-hexenol, α-pinene, and linalool, respectively; at plant maturity, all volatiles were either close to the LLOQ (lowest limit of quantitation) or not detected. Consistent with previous studies significant relationships (r ≥ 0.92; P < 0.05) were individuated within volatiles and temperature and relative humidity of the sections. However, correlations were all negative and were mainly attributed to the relevant effect of the enclosure on the final sampling conditions. Overall, levels found were at least 15 folds lower than the given Risk and LCI values of the EU-LCI protocol for indoor environments, suggesting low BVOC exposure in the i-RTG. Statistical outcomes demonstrated the applicability of the static enclosure technique for fast BVOC emissions survey inside green retrofitted spaces. However, providing high sampling performance over entire BVOCs collection is recommended to reduce sampling error and incorrect estimation of the emissions.

International audience; Exchanges of biogenic volatile organic compounds (BVOC) between plants and the atmosphere are likely to vary, in amount and composition, between different plant species but also for a single plant during its development. However, the effect of plant development stages, including senescence, on BVOC exchanges remains poorly investigated, especially in the case of crop plants. We investigated the BVOC exchange patterns for wheat plants, the most grown crop species worldwide, during seed maturation, senescence and after harvest. Fluxes were measured online, in situ, at the plant scale by combining automated chambers and a Proton Transfer - Reaction Quadrupole ion guide - Time of Flight - Mass Spectrometer (PTR-Qi-Tof-MS). The high resolution and sensitivity of this method enabled the measurement of a large mass spectrum of compounds emitted at very small amounts, allowing a precise characterization of BVOC exchanges. We found that the overall BVOC emissions increased twofold during the senescence stage compared to the maturation stage. Methanol was found to be the most emitted compound (49-60% of the overall flux on a molar basis) followed by acetone (7.5-8.2% of the overall flux on a molar basis) during each developmental stage investigated. Acetaldehyde was another major emitted compound contributing mainly during late senescence to the overall flux (9.7%). When normalized for temperature and light conditions, most BVOC emissions increased during senescence, showing a clear effect of senescence on BVOC exchanges. Chamber emissions were comparable to whole ecosystem fluxes measured at the same site by eddy covariance the previous year. The OH reactivity of the emitted compounds was evaluated based on known reaction rate constants and was the largest during the first senescence stage, peaking at 12 s(-1) in the chambers. The results of this study show the need for considering plant phenology when computing BVOC emissions from crops.

Jane EM GibbsSchool of Medicine, Griffith University, Gold Coast, Queensland, AustraliaPurpose: Prevailing opinion is that wind-pollinated plants affect asthma negatively and that insect- pollinated ones do not. “Thunderstorm” asthma, too, is attributed to bursting grass pollens. Additional biogenic volatile organic compounds (BVOCs) are identified here. Essential oils’ BVOCs are inhaled from plants, oil diffusers, candles, room “fresheners”, perfumes, and hygiene products. Claims of BVOC “safety” for sensitive respiratory systems are questioned.Methods: Fourteen volunteers, of mixed-age and gender, with seasonal asthma recorded peak expiratory flow (PEF) and 11 symptom scores. BVOCs were collected on Tenax tubes from ambient air in autumn and spring, as were live flower emissions, before and after a thunderstorm. Gas chromatography–mass spectrometry analysis identified frequently occurring BVOCs. Air spora, meteorological, outdoor air pollution variables, and BVOCs predict respiratory symptoms in univariate linear regression models, seasonally.Results: Increased pinene, camphor, linalool, linalyl acetate, benzaldehyde, and benzoic acid predict respiratory symptoms, including reduced PEF, and increased nasal congestion; day length, atmospheric pressure and temperature predict symptoms in both seasons, differently; other variables predict a range of symptoms (0.0001≤p≤0.05). Thunder predicts different BVOC emissions in spring, compared to autumn (p≤0.05). An uncut Grevillea flower emitted linalool and hexenal before a storm; the latter is also emitted from cut grass. Increased nitrogen oxides and pinene in autumn may combine to form harmful oxidation products.Conclusion: This research supports BVOCs as contributors to seasonal asthma and allergic rhinitis, and “thunderstorm” asthma. Pinene emissions from Myrtaceae species (Eucalyptus, Melaleuca, Leptospermum, Callistemon), Brassicaceae (canola), and conifers, worldwide, may induce respiratory inflammation and maintain it, by inhibiting eosinophilic apoptosis. Widely used essential oil products containing BVOCs, like linalool, are associated here with respiratory symptoms. Lagged responses suggest that users’ cognitive associations between exposure and response are unlikely, increasing potential for impaired health for vulnerable children.Keywords: asthma, allergic rhinitis, BVOC, terpenes, Eucalyptus, essential oils

Isoprene and monoterpenes (MTs) are among the most abundant and reactive volatile organic compounds produced by plants (biogenic volatile organic compounds). We conducted a meta-analysis to quantify the mean effect of environmental factors associated to climate change (warming, drought, elevated CO2 , and O3 ) on the emission of isoprene and MTs. Results indicated that all single factors except warming inhibited isoprene emission. When subsets of data collected in experiments run under similar change of a given environmental factor were compared, isoprene and photosynthesis responded negatively to elevated O3 (-8% and -10%, respectively) and drought (-15% and -42%), and in opposite ways to elevated CO2 (-23% and +55%) and warming (+53% and -23%, respectively). Effects on MTs emission were usually not significant, with the exceptions of a significant stimulation caused by warming (+39%) and by elevated O3 (limited to O3 -insensitive plants, and evergreen species with storage organs). Our results clearly highlight individual effects of environmental factors on isoprene and MT emissions, and an overall uncoupling between these secondary metabolites produced by the same methylerythritol 4-phosphate pathway. Future results from manipulative experiments and long-term observations may help untangling the interactive effects of these factors and filling gaps featured in the current meta-analysis.

Multiple positive effects that forests have on human health and overall well-being have been reported widely in the literature. Still, multiple elements of this relationship remain unidentified and unexplained. In this study, the composition of leaf volatile organic compounds (BVOCs) content in three common coniferous species: the Austrian pine (Pinus nigra), Scots pine (Pinus sylvestris) and Spruce (Picea abies), was analyzed. The specificity of BVOCs content in the examined species and their genotypes is observed as a plant potential to evaporate these organic compounds and potentially improve human health and well-being. Principal component analysis applied on BVOCs content among species showed significant differences between compounds that have previously been characterized as having positive effects on human health by acting as anticancer, anti-inflammatory, antiviral and antibacterial. Variations among genotypes of the investigated species were observed in the content of BVOCs relevant for human health improvement, such as limonene, terpinolene, β-pinene, linalool, camphene, camphor, citronellol and α-cadinol. The observed intra- and inter-species variations in the BVOCs content provide an appropriate base for further research on the forest–human health relationship, breeding and selection of the most suitable genotypes for human health improvement, and could I mpact the sustainable management of forests.

The field of plant-microbe interactions mediated by Biogenic Volatile Organic Compounds (BVOCs) still faces several limitations due to the lack of reliable equipment. We present a novel device designed to evaluate in vitro plant-microbe volatile interactions, the plant-microbe VOC Chamber. It was tested by evaluating the effects exerted on wheat development by volatiles from three Trichoderma harzianum strains, a wild type and two genetically modified strains; one expressing the tri5 gene, which leads to the synthesis and emission of the volatile trichodiene, and the other by silencing the erg1 gene, impairing ergosterol production. The wild type and the erg1-silenced strain enhanced fresh weight and length of the aerial part, but reduced root dry weight. Interestingly, no differences were found between them. Conversely, the tri5-transformant strain reduced root and aerial growth compared to the control and the other strains. No differences were observed regarding chlorophyll fluorescence quantum yield and leaf chlorophyll content, suggesting that the released BVOCs do not interfere with photosynthesis. The plant-microbe VOC Chamber proved to be a simple and reliable method to evaluate the in vitro effects of microbial BVOCs on plant development, perfect for the screening of microorganisms with interesting volatile traits. Availability of data and materials The data that support the findings of this study are available from the corresponding authors (Antonio Encina and Samuel Álvarez-García) upon reasonable request. All microbiological strains used in this study will be made available to researchers upon reasonable request. VOC Chambers will be made available to researchers upon reasonable request, unless commercial agreements reached with third parties regarding the patent exploitation prohibit it (in which case the VOC Chambers should be available in the market). SI

Tropospheric ozone (O3) affects isoprenoid emissions, and floral emissions in particular, which may result in potential impacts on the interactions of plants with other organisms. The effects of ozone (O3) on isoprenoid emissions have been investigated for many years, while knowledge on O3 effects on floral emissions is still scarce and the relevant mechanism has not been clarified so far. We investigated the effects of O3 on floral and foliar isoprenoid emissions (mainly isoprene, monoterpenes and sesquiterpenes) and their synthase substrates from three rose varieties (CH, Rosa chinensis Jacq. var. chinensis; SA, R. hybrida 'Saiun'; MO, R. hybrida 'Monica Bellucci') at different exposure durations. Results indicated that the O3-induced stimulation after short-term exposure (35 days after the beginning of O3 exposure) was significant only for sesquiterpene emissions from flowers, while long-term O3 exposure (90 days after the beginning of O3 exposure) significantly decreased both foliar and floral monoterpene and sesquiterpene emissions. In addition, the observed decline of emissions under long-term O3 exposure resulted from the limitation of synthase substrates, and the responses of emissions and substrates varied among varieties, with the greatest variation in the O3-sensitive variety. These findings provide important insights on plant isoprenoid emissions and species selection for landscaping, especially in areas with high O3 concentration.

Isoprene emission is more sensitive than photosynthesis to prolonged water and heat stress in hybrid poplar, and this reflects depletion of isoprene precursor pools under severe combined stress., Isoprene emissions have been considered as a protective response of plants to heat stress, but there is limited information of how prolonged heat spells affect isoprene emission capacity, particularly under the drought conditions that often accompany hot weather. Under combined long-term stresses, presence of isoprene emission could contribute to the maintenance of the precursor pool for rapid synthesis of essential isoprenoids to repair damaged components of leaf photosynthetic apparatus. We studied changes in leaf isoprene emission rate, photosynthetic characteristics, and antioxidant enzyme activities in two hybrid Populus clones, Nanlin 1388 (relatively high drought tolerance) and Nanlin 895 (relatively high thermotolerance) that were subjected to long-term (30 d) soil water stress (25% versus 90% soil field capacity) combined with a natural heat spell (day-time temperatures of 35–40 °C) that affected both control and water-stressed plants. Unexpectedly, isoprene emissions from both the clones were similar and the overall effects of drought on the emission characteristics were initially minor; however, treatment effects and clonal differences increased with time. In particular, the isoprene emission rate only increased slightly in the Nanlin 895 control plants after 15 d of treatment, whereas it decreased by more than 5-fold in all treatment × clone combinations after 30 d. The reduction in isoprene emission rate was associated with a decrease in the pool size of the isoprene precursor dimethylallyl diphosphate in all cases at 30 d after the start of treatment. Net assimilation rate, stomatal conductance, the openness of PSII centers, and the effective quantum yield all decreased, and non-photochemical quenching and catalase activity increased in both control and water-stressed plants. Contrary to the hypothesis of protection of leaf photosynthetic apparatus by isoprene, the data collectively indicated that prolonged stress affected isoprene emissions more strongly than leaf photosynthetic characteristics. This primarily reflected the depletion of isoprene precursor pools under long-term severe stress.

Willow (Salix spp.) trees are commonly used in short rotation coppices (SRC) to produce renewable energy. However, these plants are also known to emit high concentrations of biogenic volatile organic compounds (BVOCs), which have a large influence on air quality. Many different clones of commercially used Salix varieties exist today, but only a few studies have focused on BVOC emissions from these newer varieties. In this study, four varieties commercially propagated for biofuel production have been studied on a leaf-scale in the southern part of Sweden. The trees had either their first or second growing season, and measurements on BVOC emissions were done during the growing season in 2017 from the end of May to the beginning of September. Isoprene was the dominant emitted compound for all varieties but the average emission amongst varieties varied from 4.00 to 12.66 &micro, g gdw&minus, 1 h&minus, 1. Average monoterpene (MT) (0.78&ndash, 1.87 &micro, 1) and sesquiterpene (SQT) emission rates (0.22&ndash, 0.57 &micro, 1) differed as well among the varieties. Besides isoprene, other compounds like ocimene, linalool and caryophyllene also showed a response to light but not for all varieties. Younger plants had several times higher emissions of non-isoprenoids (other VOCs) than the corresponding 1-year-old trees. The conclusions from this study show that the choice of variety can have a large impact on the regional BVOC emission budget. Genetics, together with stand age, should be taken into account when modelling BVOC emissions on a regional scale, for example, for air quality assessments.

Forest trees are a major source of biogenic volatile organic compounds (BVOCs). Terpenes and terpenoids are known as the main BVOCs of forest aerosols. These compounds have been shown to display a broad range of biological activities in various human disease models, thus implying that forest aerosols containing these compounds may be related to beneficial effects of forest bathing. In this review, we surveyed studies analyzing BVOCs and selected the most abundant 23 terpenes and terpenoids emitted in forested areas of the Northern Hemisphere, which were reported to display anti-inflammatory activities. We categorized anti-inflammatory processes related to the functions of these compounds into six groups and summarized their molecular mechanisms of action. Finally, among the major 23 compounds, we examined the therapeutic potentials of 12 compounds known to be effective against respiratory inflammation, atopic dermatitis, arthritis, and neuroinflammation among various inflammatory diseases. In conclusion, the updated studies support the beneficial effects of forest aerosols and propose their potential use as chemopreventive and therapeutic agents for treating various inflammatory diseases.

Biogenic volatile organic compound (BVOC) emissions from subarctic ecosystems have shown to increase drastically in response to a long-term temperature increase of only 2°C. We assessed whether this increase takes place already after 3 years of warming and how the increase changes over time. To test this, we measured BVOC emissions and CO2 fluxes in a field experiment on a subarctic wet heath, where ecosystem plots were subjected to passive warming by open top chambers for 3 (OTC3) or 13 years (OTC13) or were kept as unmanipulated controls. Already after 3 years of moderate temperature increase of 1–2°C, warming increased the emissions of isoprene (five- to sixfold) and monoterpenes (three- to fourfold) from the subarctic heath. The several-fold higher BVOC emissions in the warmed plots are likely a result of increased vegetation biomass and altered vegetation composition as a shift in the species coverage was observed already after 3 years of warming. Warming also increased gross ecosystem production and ecosystem respiration, but the increases were much lower than those for BVOCs. Our results demonstrate that the strong BVOC responses to warming already appeared after 3 years, and the BVOC and CO2 fluxes had acclimated to this warming after 3 years, showing no differences with another 10 years of warming. This finding has important implications for predicting CO2 and BVOC fluxes in subarctic ecosystems. (Less)

Background Biogenic volatile organic compounds (BVOC) emitted by plants play an important role for ecological and physiological processes, for example as response to stressors. These emitted compounds are involved in chemical processes within the atmosphere and contribute to the formation of aerosols and ozone. Direct measurement of BVOC emissions requires a specialized sample system in order to obtain repeatable and comparable results. These systems need to be constructed carefully since BVOC measurements may be disturbed by several side effects, e.g., due to wrong material selection and lacking system stability. Results In order to assess BVOC emission rates, a four plant chamber system was constructed, implemented and throughout evaluated by synthetic tests and in two case studies on 3-year-old sweet chestnut seedlings. Synthetic system test showed a stable sampling with good repeatability and low memory effects. The first case study demonstrated the capability of the system to screen multiple trees within a few days and revealed three different emission patterns of sweet chestnut trees. The second case study comprised an application of drought stress on two seedlings compared to two in parallel assessed seedlings of a control. Here, a clear reduction of BVOC emissions during drought stress was observed. Conclusion The developed system allows assessing BVOC as well as CO2 and water vapor gas exchange of four tree specimens automatically and in parallel with repeatable results. A canopy volume of 30 l can be investigated, which constitutes in case of tree seedlings the whole canopy. Longer lasting experiments of e.g., 1–3 weeks can be performed easily without any significant plant interference. Electronic supplementary material The online version of this article (doi:10.1186/s13007-017-0166-6) contains supplementary material, which is available to authorized users.

Volatile Organic Compounds (VOC) play a key role in atmospheric chemistry influencing climate and air quality. Vegetation is the main source of VOC, accounting for 90% of biogenic emissions (BVOC). Agricultural crops in Europe are estimated to contribute 27% of total BVOC emissions but remain poorly studied. In this work, we study the exchange of BVOC by wheat, rapeseed and maize, the main agricultural species in France in terms of cultivated area. The fluxes were measured in the field at the plant level with dynamic automated chambers coupled to a PTR-Qi-Tof-MS spectrometer. Fluxes of up to 997 compounds could be measured with this highly sensitive instrument. Chapter 1 presents a review of BVOC emission mechanisms, flux measurement methods, experimental results on BVOC exchanges in agricultural systems, and mathematical models of emissions. Chapter 2 describes the measurement site and the experimental setup. Chapter 3 presents BVOC fluxes measured during one week for each species. Emissions were dominated by methanol (55-85% of total emissions) followed by acetone and acetaldehyde. The 10 most emitted compounds excluding methanol accounted for more than 50% of total emissions and the 100 most emitted compounds accounted for more than 90%. The measured fluxes showed little intra-species variation but large inter-species variations with total net fluxes of 0.11±0.02 µg_BVOC g_DW^(-1) h^(-1) for maize, 1.5±0.7 µg_COVB g_MS^(-1) h^(-1) for wheat, and 9.1±2.4 µg_COVB g_MS^(-1) h^(-1) for rapeseed. Finally, standard emission factors for isoprene and monoterpenes were evaluated for each species, constituting the first known estimates for rapeseed. Chapter 4 examines the influence of developmental stages, and particularly of senescence, on BVOC emissions from wheat. We report a doubling of total emissions during senescence compared to maturation, with, in particular, an increase in the contribution of acetaldehyde (1.6% of total emissions during maturation and 9.7% during senescence) and acetic acid (0.7% during maturation and 2.7% during senescence). In Chapter 5 the main parameters of the MEGAN 2.1 model are estimated for the three species and the fluxes of six main compounds measured for rapeseed at the plant level by the dynamic chambers are compared with measurements by Eddy Covariance at the ecosystem level in order to evaluate the representativeness of chamber measurement. This work shows the heterogeneity of BVOC exchanges by agricultural plants and the data generated should contribute to the improvement of emission models.; Les Composés Organiques Volatils (COV) sont des acteurs importants de la chimie de l’atmosphère influençant le climat et la qualité de l’air. La végétation en est la principale source représentant 90% des émissions d’origine biogénique (COVb). Il est estimé que les couverts agricoles contribueraient à 27% des émissions totales de COVb en Europe mais ces émissions restent mal connues. Dans ce travail, les échanges de COVb par le blé, le colza, et le maïs sont étudiés, ces espèces agricoles étant les principales en France et dans le monde, en termes de surface cultivée. Des flux de COVb ont été mesurés au champ, au niveau de la plante, avec des chambres dynamiques couplées à un spectromètre de masse PTR-Qi-Tof-MS. Les échanges de 997 composés ont pu être mesurés grâce à cet instrument de haute sensibilité. Dans le Chapitre 1 nous présentons une revue des mécanismes d’émission des COVb, des méthodes de mesure de flux, des résultats expérimentaux sur les échanges de COVb pas les systèmes agricoles, et des modèles mathématiques d’émission par les écosystèmes. Dans le Chapitre 2 nous décrivons la campagne et les dispositifs de mesure. Dans le Chapitre 3 nous présentons les résultats des échanges de COVb mesurés durant une semaine pour chaque espèce. Les émissions étaient dominées par le méthanol (55-85% des émissions totales), suivi de l’acétone et l’acétaldéhyde. Les 10 composés les plus émis, hors méthanol, représentaient plus de 50% des émissions totales, et les 100 composés les plus émis plus de 90%. Les flux de COVb présentaient peu de variation intra-espèce mais d’importantes variations inter-espèces, avec des flux net totaux de 0.11±0.02 µg_COVB g_MS^(-1) h^(-1) pour le maïs, 1.5±0.7 µg_COVB g_MS^(-1) h^(-1) pour le blé, et 9.1±2.4 µg_COVB g_MS^(-1 ) h^(-1) pour le colza. Finalement les facteurs d’émission standard de l’isoprène et des monoterpènes ont été évalués pour chaque espèce, constituant les premières estimations connues pour le colza. Dans le Chapitre 4 nous étudions l’influence du stade de développement, et plus particulièrement de la senescence, sur les émissions de COVb par le blé. Nous montrons un doublement des émissions totales pendent la sénescence par rapport à la maturation, avec notamment une augmentation de la contribution de l’acétaldéhyde (1.6% des émissions totales pendant la maturation et 9.7% pendant la sénescence) et de l’acide acétique (0.7% pendant la maturation et 2.7% pendant la sénescence) aux émissions totales. Dans le Chapitre 5 nous estimons les principaux paramètres du modèle MEGAN 2.1 pour les trois espèces de plantes. Nous comparons les flux des six principaux composés mesurés pour le colza à l’échelle de la plante par les chambres dynamiques avec des mesures par Eddy Covariance à l’échelle de l’écosystème, afin d’évaluer la représentativité des mesures en chambre. Ce travail montre l’hétérogénéité des échanges de COVb par les plantes agricoles et les données générées pourront contribuer à l’amélioration des modèles d’émission.

Isoprene is a highly abundant biogenic volatile organic compound (BVOC) that is emitted to the atmosphere in amounts approximating to those of methane. The effects that isoprene has on Earth’s climate are both significant and complex, however, unlike methane, very little is known about the biological degradation of this environmentally important trace gas. Here, we review the mechanisms by which bacteria catabolise isoprene, what is known about the diversity of isoprene degraders in the environment, and the molecular tools currently available to study their ecology. Specifically, we focus on the use of probes based on the gene encoding the α-subunit of isoprene monooxygenase, isoA, and DNA stable-isotope probing (DNA-SIP) alone or in combination with other cultivation-independent techniques to determine the abundance, diversity, and activity of isoprene degraders in the environment. These parameters are essential in order to evaluate how microbes might mitigate the effects of this important but neglected climate-active gas. We also suggest key aspects of isoprene metabolism that require further investigation in order to better understand the global isoprene biogeochemical cycle.

In the present work the composition of biogenic volatile organic compounds (BVOCs) and the essential oil (EO) of Helichrysum araxinum Takht. ex Kirp. aerial parts, together with the antimicrobial activity, were investigated. The results showed the prevalence of sesquiterpene hydrocarbons in both spontaneous emissions as well as in the EO. The main compounds of BVOCs were γ-curcumene (10.7%), γ-muurolene (9.2%), and β-selinene (8.5%). This latter constituent also showed a similar amount in the EO and represented the most abundant compounds together with α-selinene (8.0%). It is Interesting to note the same percentage of monoterpene hydrocarbons (MHs) in both the aroma profile and the EO (18.0%) with the same most abundant compounds: β-pinene (6.3% in BVOCs vs. 5.1% in EO, respectively) and limonene (4.5% in VOCs vs. 4.9% in EO, respectively). With regard to the antimycotic activity, the EO showed to be inactive against the tested strains, while a moderate antibacterial activity was shown against Staphylococcus isolates.

Biogenic volatile organic compounds (BVOC) play an important role in global environmental chemistry and climate. In the present work, biogenic emissions from China in 2017 were estimated based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN). The effects of BVOC emissions on ozone and secondary organic aerosol (SOA) formation were investigated using the WRF-CMAQ modeling system. Three parallel scenarios were developed to assess the impact of BVOC emissions on China's ozone and SOA formation in July 2017. Biogenic emissions were estimated at 23.54 Tg/yr, with a peak in the summer and decreasing from southern to northern China. The high BVOC emissions across eastern and southwestern China increased the surface ozone levels, particularly in the BTH (Beijing-Tianjin-Hebei), SCB (Sichuan Basin), YRD (Yangtze River Delta) and central PRD (Pearl River Delta) regions, with increases of up to 47 μg m−3 due to the sensitivity of VOC-limited urban areas. In summer, most SOA concentrations formed over China are from biogenic sources (national average of 70%). And SOA concentrations in YRD and SCB regions are generally higher than other regions. Excluding anthropogenic emissions while keeping biogenic emissions unchanged results that SOA concentrations reduce by 60% over China, which indicates that anthropogenic emissions can interact with biogenic emissions then facilitate biogenic SOA formation. It is suggested that controlling anthropogenic emissions would result in reduction of both anthropogenic and biogenic SOA.

Our knowledge on the biosynthesis of several biogenic volatile organic compounds (BVOCs) is still limited. In this regard, natural abundant stable carbon isotope ratios (δ13C) of BVOCs may provide a powerful tool to evaluate different metabolic pathways. In the present study, BVOC emissions, and their carbon isotope composition from two Mediterranean species, Quercus suber L. and Cistus ladanifer L. were investigated under field conditions in June and July 2018. Soil water content decreased between these months, which was reflected by an increase of the photosynthetic discrimination from −27.7 ± 0.2 to −26.2 ± 0.2‰ in Q. suber and from −27.0 ± 0.3 to −26.1 ± 0.3‰ in C. ladanifer. This change made an impact on the signatures of various BVOCs, which varied along a very broad range of −28.0 to −42.6‰ in June and −23.7 to −32.9‰ in July. Hence, the increasing photosynthetic discrimination had a cascading effect on the natural carbon isotope composition of the emitted BVOCs over time. Consistent differences in compound classes occurred among species and seasons: acyclic monoterpenoids were the most 13C enriched compound class (−23.7 to −31.3‰), followed by slightly more depleted cyclic monoterpenes (−27.6 to −32.9‰) and sesquiterpenes (−26.4 to −32.1‰). The detected oxygenated cyclic monoterpenoids (−31.5 to −37.0‰) and benzenoid aromatic compounds (−30.6 to −42.6‰) were strongly 13C depleted. Hierarchical clustering based on δ13C values confirmed the grouping of BVOCs with similar chemical structures to the same cluster. Hence, we suggest that isotopic fractionation occurs during the cyclization and oxygenation processes of monoterpenoids, as well as during the synthesis of volatile benzenoid aromatic compounds. The differences in δ13C values between BVOCs were consistent, although we collected BVOCs under highly varying light conditions, air temperatures, emission rates and from two different species. Here, we demonstrate that the natural carbon isotope composition may provide a robust framework to elucidate biosynthetic pathways of various BVOCs under field conditions.

Biogenic volatile organic compounds (BVOC) are strongly emitted by forests and crops in the atmosphere. They are very reactive towards nitrate radical, the main tropospheric oxidant during the night, and play a key role in atmospheric chemistry. These reactions lead to the formation of a variety of functionalized products (organic nitrates, carbonyl compounds ...) and to large amounts of secondary organic aerosols. Organic nitrates are the main nitrogen oxides reservoir. They directly influence reactive nitrogen and ozone budgets. Secondary organic aerosol has direct and indirect impacts on climate, due to its formation, its optical and hygroscopic properties and its chemical composition. The aim of this work is to understand these processes at the molecular scale, through kinetic and mechanistic studies of NO3 radical oxidation of several BVOCs.Kinetic and mechanistic studies have been performed for three monoterpenes ((C10H16), γ- and α-terpinene and terpinolene) and one sesquiterpene ((C15H24), β-caryophyllene) in atmospheric simulation chambers. These compounds have been chosen to highlight the influence of their chemical structures on their reactivities and to fill the lack of experimental data about their chemistry in the literature.For the kinetic part, rate constants have been measured with both relative and absolute methods. Due to their high reactivities, this study has requiered the development on the simulation chamber of an IBB-CEAS ((Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) analysis pathway to measure nitrate radical at the ppt level. Mechanistic studies have been also conducted to identify and quantify the main reaction products. Organic nitrates and SOA yields have been calculated. Detected products allowed proposing reaction mechanisms., Les composés organiques volatils biogéniques (COVB) sont fortement émis dans l’atmosphère par les forêts et les cultures. Très réactifs vis-à-vis du radical nitrate NO3, principal oxydant nocturne dans la troposphère, ils ont une importance majeure dans la chimie atmosphérique. En effet, cette réaction mène à la formation d’un large panel de produits de réaction en phase gazeuse fonctionnalisés (nitrates organiques, composés carbonylés, ...) et une large fraction d’aérosols organiques secondaires. Les nitrates organiques constituent des espèces réservoirs d’oxydes d’azote dans l’atmosphère et influencent directement le bilan d’azote réactif et ainsi les niveaux d’ozone. L’aérosol organique secondaire, de par sa formation, ses propriétés optiques et hygroscopiques ainsi et sa composition chimique a un impact direct et indirect sur le climat. Ce travail a pour but la compréhension de ces processus à l’échelle moléculaire à travers une étude cinétique et mécanistique des réactions d’oxydation de plusieurs COVB par le radical NO3.Ainsi, les réactions d’oxydation par le radical NO3 de trois monoterpènes ((C10H16), γ- et α-terpinène et le terpinolène) et un sesquiterpène ((C15H24), le β-caryophyllène) ont été invesitguées en chambre de simulation atmosphérique. Les composés ont été choisis d’une part pour mettre en évidence l’influence de leur structure chimique sur leur réactivité et d’autre part, pour combler les manques de données expérimentales dans la littérature sur la chimie de ces composés.Pour la partie cinétique, les constantes de vitesse ont été mesurées à la fois par la méthode de cinétique absolue et par celle de cinétique relative. Les réactions chimiques étudiées étant très rapides, cette étude a nécessité au préalable le développement sur la chambre de simulation atmosphérique d’une voie d’analyse spectroscopique IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) pour la mesure des radicaux nitrates dans la gamme du ppt. Des études mécanistiques ont également été menées afin d’identifier et de quantifier les principaux produits de réaction. Les rendements de nitrates organiques, d’AOS ont été calculés. Les produits détectés ont permis d’établir des mécanismes réactionnels.

Climate sensitive urban planning involves the implementation of green infrastructure as one measure to mitigate excessive heat in urban areas. Depending on thermal conditions, certain trees tend to emit more biogenic volatile organic compounds, which act as precursors for ozone formation, thus hampering air quality. Combining a theoretical approach from a box model analysis and microscale modeling from the microclimate model ENVI-met, we analyze this relationship for a selected region in Germany and provide the link to air quality prediction and climate sensitive urban planning. A box model study was conducted, indicating higher ozone levels with higher isoprene concentration, especially in NO-saturated atmospheres. ENVI-met sensitivity studies showed that different urban layouts strongly determine local isoprene emissions of vegetation, with leaf temperature, rather than photosynthetic active radiation, being the dominant factor. The impact of isoprene emission on the ozone in complex urban environments was simulated for an urban area for a hot summer day with and without isoprene. A large isoprene-induced relative ozone increase was found over the whole model area. On selected hot spots we find a clear relationship between urban layout, proximity to NOx emitters, tree-species-dependent isoprene emission capacity, and increases in ozone concentration, rising up to 500% locally.

Background and aims: Isoprene and monoterpenes account for approximately two thirds of the biogenic volatile organic compounds (BVOC) emitted annually by vegetation into the atmosphere. Previous research focussed on the magnitude of and controls on emissions of these two compounds by emitting plant species, while the role of soils and non-emitting plant species as potential sinks has been mostly ignored. The objective of the present study is to characterize the deposition of isoprene and α-pinene (a monoterpene) to non-emitting grassland plant mesocosms. Methods: We conducted a laboratory experiment with mesocosms of two forb and one graminoid plant species. Plants and soils together and bare soils only were subject to increasing ambient isoprene and α-pinene concentrations (0–10 ppbv) and the corresponding BVOC exchange rates were quantified. Results: Our major findings are that (i) soils were the dominant sink for the deposition of α-pinene and isoprene in grassland mesocosms, (ii) the presence of above-ground biomass of non-emitting plant species decreased the isoprene and α-pinene deposition in the majority of all cases, and (iii) the net deposition correlated inversely with the ambient concentrations. Conclusions: Our results call for a more in-depth analysis of soil BVOC exchange to better estimate the contribution of soils to the ecosystem-atmosphere BVOC exchange.

Atmospheric aerosols influence our climate and air quality. Aerosol particles in the atmosphere are transformed through many different physical and chemical reactions. A substantial fraction of the particles in the atmosphere are of secondary origin, formed as a result of gas to particle conversion. The formation process of secondary organic aerosols (SOA) from oxidation of volatile organic compounds (VOC) is currently not fully understood. The objective of this thesis is to contribute to the understanding of factors important for secondary particle formation by simulating certain atmospheric processes in a flow reactor and by measurements of organic compounds in the ambient atmosphere. This work focuses on the formation of secondary organic particles via gas to particle conversion, their chemical composition and the volatility of the compounds. These factors are important for understanding the formation and evolution of secondary particles in the atmosphere, which in turn is important for making predictions about our future climate. The chemical composition of SOA was studied using a chemical ionization high-resolution time-of-flight mass spectrometer connected to a Filter Inlet for Gases and Aerosols (FIGAERO-ToF-CIMS). The analysis was performed on samples from three sites: a boreal forest in Europe, a temperate forest in North America and a semi-urban location near a major city in Asia. In order to model SOA and thus be able to predict its impact on society, in particular relating to climate change and health issues, accurate models for SOA formation are needed. The basis for such models includes understanding gas to particle partitioning and the factors that influence this partitioning. In addition, knowledge of the compounds in the particles is needed. The work revealed ways in which anthropogenic pollution could affect the partitioning and consequently the formation of SOA. It was shown that equilibrium phase partitioning behaves as predicted under some circumstances, such as when the air was not affected by anthropogenic pollution. However, when the air masses were affected by anthropogenic pollution, equilibrium phase partitioning does not behave as expected, due to restrictions in uptake and the aerosol not being in equilibrium. This effect was especially seen for highly oxygenated compounds.

Biogenic volatile organic compounds (BVOC) are mainly emitted from vegetation. However there is still little information on BVOC exchanges with crops. In this study we measured fluxes of BVOC from wheat, maize and rapeseed crops near Paris at the plant level during a full-week period for each species. We used dynamic automated chambers coupled to a Proton Transfer Reaction, Quadrupole ion guide, Time of Flight mass spectrometer (PTR-Qi-Tof-MS) instrument for online measurements of BVOC. Our results confirm the hypothesis that many unexplored compounds contribute to BVOC exchanges between crops and the atmosphere, although for all plant species methanol was dominating the emissions (55–85% of the sum of the BVOC exchanges fluxes on a mass basis) followed by acetone and acetaldehyde. The 10 most exchanged compounds, excluding methanol, contributed more than 50% of the summed fluxes and the 100 most exchanged contributed to more than 90%. The summed BVOC emission and deposition presented large interspecies variations, but limited intra-species variability, with a summed net flux of 0.11 ± 0.02 μgBVOC gDW−1 h−1 for maize, 1.5 ± 0.7 μgBVOC gDW−1 h−1 for wheat, and 9.1 ± 2.4 μgBVOC gDW−1 h−1 for rapeseed. The 10 most emitted compounds were mostly emitted during the day and were correlated with both photosynthetically active radiation and temperature and anti-correlated with relative humidity. This study provides the first evaluation so far of the biosphere-atmosphere fluxes for several BVOC. In particular we provide a first evaluation of standard emission factor for isoprene and monoterpene for wheat and rapeseed at their respective growth stages. This study is however limited to a week period at a given stage for each species and at the plant level.

Drought is a major environmental constrain affecting plant performance and survival, particularly in Mediterranean ecosystems. Terpenoids may play a protective role under these conditions, however, observations of drought effects on plant terpenoid emissions are controversial ranging from decreased emissions to unaffected or increased release of terpenoids. In the present study we investigated terpenoid emissions of cork oak (Quercus suber) and gum rockrose (Cistus ladanifer) in response to summer drought stress in 2017. Pre-dawn leaf water potential (ΨPD) decreased from -0.64 to -1.72 MPa in Q. suber and from -1.69 to -4.05 MPa in C. ladanifer, indicating a transition from mild to severe drought along summer. Total terpenoid emissions decreased with drought, but differed significantly between species (p < 0.001) and in response to ΨPD, air temperature and assimilation rates. C. ladanifer emitted a large variety of >75 compounds comprising monoterpenes, sesquiterpenes and even diterpenes, which strongly decreased from 1.37 ± 0.23 μg g-1h-1 to 0.40 ± 0.08 μg g-1h-1 (p < 0.001) in response to drought. Total emission rates were positively correlated to air temperature (p < 0.001). C. ladanifer behavior points toward terpenoid leaf storage depletion and reduced substrate availability for terpenoid synthesis with increasing drought, most likely accelerated by high air temperatures. Q. suber emitted mainly monoterpenes and emissions declined significantly from June (0.50 ± 0.08 μg g-1h-1) to August (0.29 ± 0.02 μg g-1h-1) (p < 0.01). Emission rates were weakly correlated with net assimilation rates (R2 = 0.19, p < 0.001), but did not respond strongly to ΨPD and air temperature. Early onset of drought in 2017 most likely reduced plant metabolism in Q. suber, resulting in diminished, but stable terpenoid fluxes. Calculation of standard emission factors (at 30°C) revealed contrasting emission patterns of decreasing, unaffected, or increasing fluxes of single terpenoid compounds. Unaffected or drought-enhanced emissions of compounds such as α-pinene, camphene or manoyl oxide may point toward a specific role of these terpenoids in abiotic stress adaptation. In conclusion, these results suggest a strong negative, but species- and compound-specific effect of severe drought on terpenoid fluxes in Mediterranean ecosystems.

© 2018 Elsevier Ltd Emissions of biogenic volatile organic compounds (BVOCs) from natural ecosystems impact atmospheric chemistry as well as biological interactions and even soil biogeochemical processes. Plant litter emits substantial amounts of BVOCs. These emissions may contribute to total ecosystem emissions especially in the Arctic where the living plant biomass is low and the amount of litter is expected to increase as the deciduous shrubs expand in response to a warmer climate. Here, we incubated in the laboratory litter from the evergreen Cassiope tetragona and deciduous Salix spp. from a high arctic and a low arctic location. The 8-week-long incubation was conducted with temperature increasing from 5 °C to 26 °C, mimicking the transition from winter to summer. BVOC emissions from the decomposing litter were sampled weekly in adsorbent cartridges and analyzed using gas chromatography–mass spectrometry, and the bacterial community composition was investigated by sequencing of PCR amplified 16S rRNA gene fragments. Our results showed that litter from C. tetragona, which is a terpenoid storing species, had higher BVOC emission rates (mainly terpenoids) than the Salix litter, which does not have specialized BVOC storing compartments. The C. tetragona litter emissions were higher in the high arctic than the low arctic samples. The emission rates from the C. tetragona litter increased during the incubation period, whereas emission rates from the Salix litter decreased, suggesting that the emissions originated from different sources and/or processes. The bacterial community composition in the Salix litter, but not in the C. tetragona litter, changed in parallel with the changes in the BVOC emissions during the incubation period. Therefore, we suggest that bacteria may be more important for the BVOC emissions from decomposing Salix litter than C. tetragona litter.

The atmospheric reactions leading to the generation of secondary organic aerosol (SOA) from the oxidation of isoprene are generally assumed to produce only racemic mixtures, but aspects of the chemical reactions suggest this may not be the case. In this review, the stereochemical outcomes of published isoprene-degradation mechanisms contributing to high amounts of SOA are evaluated. Despite evidence suggesting isoprene first-generation oxidation products do not contribute to SOA directly, this review suggests the stereochemistry of first-generation products may be important because their stereochemical configurations may be retained through to the second-generation products which form SOA. Specifically, due to the stereochemistry of epoxide ring-opening mechanisms, the outcome of the reactions involving epoxydiols of isoprene (IEPOX), methacrylic acid epoxide (MAE) and hydroxymethylmethyl-α-lactone (HMML) are, in principle, stereospecific which indicates the stereochemistry is predefined from first-generation precursors. The products from these three epoxide intermediates oligomerise to form macromolecules which are proposed to form chiral structures within the aerosol and are considered to be the largest contributors to SOA. If conditions in the atmosphere such as pH, aerosol water content, relative humidity, pre-existing aerosol, aerosol coatings and aerosol cation/anion content (and other) variables acting on the reactions leading to SOA affect the tacticity (arrangement of chiral centres) in the SOA then they may influence its physical properties, for example its hygroscopicity. Chamber studies of SOA formation from isoprene encompass particular sets of controlled conditions of these variables. It may therefore be important to consider stereochemistry when upscaling from chamber study data to predictions of SOA yields across the range of ambient atmospheric conditions. Experiments analysing the stereochemistry of the reactions under varying conditions of the above variables would help elucidate whether there is stereoselectivity in SOA formation from isoprene and if the rates of SOA formation are affected.

This study conducted analyses on biogenic volatile organic compounds (BVOC) emission sources contributing to urban ozone (O₃) concentration in Osaka Prefecture, Japan in summer 2010 by using the Weather Research and Forecasting model (WRF) version 3.5.1 and the Community Multiscale Air Quality model (CMAQ) version 5.0.1. This prefecture is characterized by highly urbanized area with small forest area. The contributions of source regions surrounding Osaka were estimated by comparing the baseline case and zero-out cases for BVOC emissions from each source region. The zero-out emission runs showed that the BVOC emissions substantially contributed to urban O₃ concentration in Osaka (10.3 ppb: 15.9% of mean daily maximum 1-h O₃ concentration) with day-by-day variations of contributing source regions, which were qualitatively explained by backward trajectory analyses. Although O₃ concentrations were especially high on 23 July and 2 August 2010, the contribution of BVOC on 23 July (35.4 ppb: 25.6% of daily maximum O₃) was much larger than that on 2 August (20.9 ppb: 14.2% of daily maximum O₃). To investigate this difference, additional zero-out cases for anthropogenic VOC (AVOC) emissions from Osaka and for VOC emissions on the target days were performed. On 23 July, the urban O₃ concentration in Osaka was dominantly increased by the transport from the northwestern region outside Osaka with large contribution of O₃ that was produced through BVOC reactions by the day before and was retained over the nocturnal boundary layer. On 2 August, the concentration was dominantly increased by the local photochemical production inside Osaka under weak wind condition with the particularly large contribution of AVOC emitted from Osaka on the day.

Biogenic volatile organic compounds (BVOCs) are trace gases other than CO2 and CH4 produced and emitted by the vegetation. The group consists of thousands of compounds in various shapes and sizes and with short atmospheric lifetimes. Some of the most common BVOC groups are called isoprene, monoterpenes and sesquiterpenes. For the plant, the emission of BVOCs is used for plant communication, attracting pollinators, to deter herbivores and to enhance abiotic stress defense against for example high temperatures, irradiation or oxidative stresses. But once released into the atmosphere, they are affecting the atmospheric chemistry which in effect alters our climate. Depending on the atmospheric composition, BVOC emissions can either enhance tropospheric ozone and indirectly prolong the lifetimes of greenhouse gases such as methane by reducing the concentration of hydroxyl radicals, or increase the formation of aerosols and cloud condensation nuclei which may mitigate the effect of greenhouse gases on global warming.It is fairly well known that BVOCs have an impact on the climate. However, whether the BVOC emissions have a warming or cooling effect on the overall climate is difficult to determine due to existing emission pattern variations both between individuals of the same species and between species. Some of the reasons which are often discussed to be influential and where there is relatively little data available are within-species genetic variation, stress response, adaptation to different weather and climatic conditions and seasonality. In this thesis, focus has been given to the importance of genetic diversity and adaptation to different growing conditions. Studies have been conducted on three European tree species with genetically identical individuals across a latitudinal gradient, stretching from Slovenia to southern Finland. The main results were that even though the emission amounts varied between sites due to differences in weather events, the progression of the growing season and insect outbreaks, the compound composition between individuals were similar both across latitudes and between measurement years. By showing compound composition stability for genetically identical trees, the results highlights the importance of taking genetic diversity into account in terms of observed emission pattern variations. The response to changing light conditions on the emission amount of different compounds was also investigated. The results uncovered that different compounds had different emission responses to changing light conditions, but that the response of the compounds were fairly similar across different species.

In many plants, biogenic volatile organic compounds (BVOCs) are produced as specialized metabolites that contribute to the characteristics of each plant. The varieties and composition of BVOCs are chemically diverse by plant species and the circumstances in which the plants grow, and also influenced by herbivory damage and pathogen infection. Plant-produced BVOCs are receptive to many organisms, from microorganisms to human, as both airborne attractants and repellants. In addition, it is known that some BVOCs act as signals to prime a plant for the defense response in plant-to-plant communications. The compositional profiles of BVOCs can, thus, have profound influences in the physiological and ecological aspects of living organisms. Apart from that, some of them are commercially valuable as aroma/flavor compounds for human. Metabolomic technologies have recently revealed new insights in biological systems through metabolic dynamics. Here, the recent advances in metabolomics technologies focusing on plant-produced BVOC analyses are overviewed. Their application markedly improves our knowledge of the role of BVOCs in chemosystematics, ecological influences, and aroma research, as well as being useful to prove the biosynthetic mechanisms of BVOCs.

International audience; Biogenic volatile organic compounds (BVOC) emitted by plants can originate from both anabolism (metabolite production through anabolic processes) and catabolism (metabolite degradation by oxidative reactions). Drought can favor leaf oxidation by increasing the oxidative pressure in plant cells. Thus, under the precipitation decline predicted for the Mediterranean region, it can be expected both strong oxidation of anabolic BVOC within leaves and, as a result, enhanced catabolic BVOC emissions. Using an experimental rain exclusion device in a natural forest, we compared the seasonal course of the emissions of the main anabolic BVOC released by Q. pubescens (isoprene and methanol) and their catabolic products (MACR+MVK+ISOPOOH and formaldehyde, respectively) after 3 years of precipitation restriction (-30% of rain). Thus, we assume that this repetitive amplified drought promoted a chronic drought. BVOC emissions were monitored, on-line, with a PTR-ToF-MS. Amplified drought decreased all BVOC emissions rates in spring and summer by around 40-50 %, especially through stomatal closure, with no effect in autumn. Moreover, ratios between catabolic and anabolic BVOC remained unchanged with amplified drought, suggesting a relative stable oxidative pressure in Q. pubescens under the water stress applied. Moreover, these results suggest a quite good resilience of this species under the most severe climate change scenario in the Mediterranean region.

Questo studio si è focalizzato sulla valutazione delle emissioni di aerosol e composti organici volatili, sia antropogenici che biogenici, e delle dinamiche evolutive che determinano la composizione atmosferica di background in area giuliana. Sono state inoltre identificate le condizioni di campionamento e le matrici vegetali più idonee per il biomonitoraggio di microinquinanti. In primo luogo è stata svolta una caratterizzazione dell’aerosol in un sito rurale del Carso triestino definendo le concentrazioni di macrocostituenti (ioni inorganici, carbonio organico ed elementare) e componenti minori, indici di combustione di biomasse (levoglucosano e Idrocarburi Policiclici Aromatici) o derivanti da fonti biogeniche (alcani dispari). È stata evidenziata una forte componente biogenica di particolato primario tipicamente legata al periodo vegetativo delle piante mentre la componente antropica è risultata limitata al periodo invernale. Uno studio di biomonitoraggio svolto con il gruppo di ricerca in lichenologia del Dipartimento di Scienze della Vita dell’ateneo giuliano mediante trapianti di Pseudevernia furfuracea alle pendici delle pre-Alpi Carniche ha analogamente evidenziato concentrazioni di IPA significative solo nella stagione fredda e invece trascurabili nel periodo estivo sia per l’assenza della sorgente riscaldamento, sia considerando la maggior degradazione associata a condizioni atmosferiche più ossidanti. In collaborazione con il Dipartimento di Agricoltura e Scienze Ambientali dell’Università di Udine è inoltre stato verificato l’accumulo invernale di IPA su piante per il verde pubblico (Elaeagnus x ebbingei, Ilex aquifolium, Laurus nobilis, Ligustrum japonicum, Photinia x fraserii e Viburnum lucidum) trapiantate in due siti della città di Udine. Si è potuto osservare in particolare un accumulo degli IPA più pesanti (più significativi dal punto di vista tossicologico) ed identificare Elaeagnus x ebbingei, Ligustrum japonicum e Laurus nobilis come specie più adatte all’impiego in studi di bioaccumulo il quale risulta correlato alla densità stomatica delle foglie. Essendo noto che le piante emettono in atmosfera considerevoli quantità di sostanze organiche volatili (BVOC) che possono reagire in atmosfera dando origine a componenti biogeniche dell’aerosol (BSOA) e non risultando disponibili in letteratura altri studi simili sull’area carsica, sono stati approntati dei metodi analitici atti alla valutazione dei flussi emissivi di BVOC e metodi atti all’individuazione di derivati ossidati degli stessi nel particolato atmosferico. Utilizzando la tecnica branch enclosure sono state studiate le emissioni stagionali e circadiane di specie vegetali autoctone (Cotinus coggygria, Quercus pubescens, Pinus nigra, Fraxinus ornus). Tra i composti identificati risulta rilevante l’isoprene, emesso essenzialmente da Quercus pubescens nelle ore centrali della giornata. Tenuto conto di parametri specie-specifici, quali il Leaf Area Index e la copertura del territorio, sono stati stimati i flussi emissivi per l’associazione Aristolochio luteae-Quercetum pubescentis, caratteristica del Carso costiero. I valori ottenuti per la scala locale sono stati confrontati con stime computazionali ottenute per aree di maggiori dimensioni implementando un modello specifico per le emissioni naturali. Fra le specie organiche secondarie riscontrate su campioni estivi del PM10 raccolto presso un sito rurale carsico si annoverano l’acido ossalico derivante dall’isoprene e l’acido pinonico derivante dal pinene. In collaborazione con l’Università di Aahrus sono anche stati analizzati composti secondari nitrossisolforati per i quali si è riscontrata una differenza significativa rispetto alle concentrazioni diurne e notturne indicando l’importanza dei processi di ossidazione fotochimica che coinvolgono specie radicaliche azotate dovute all’evoluzione long-range di emissioni antropiche quali NOx.

This paper reports the first direct eddy covariance fluxes of reactive biogenic volatile organic compounds (BVOCs) from oil palms to the atmosphere using proton-transfer-reaction mass spectrometry (PTR-MS), measured at a plantation in Malaysian Borneo. At midday, net isoprene flux constituted the largest fraction (84 %) of all emitted BVOCs measured, at up to 30 mg m−2 h−1 over 12 days. By contrast, the sum of its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) exhibited clear deposition of 1 mg m−2 h−1, with a small average canopy resistance of 230 s m−1. Approximately 15 % of the resolved BVOC flux from oil palm trees could be attributed to floral emissions, which are thought to be the largest reported biogenic source of estragole and possibly also toluene. Although on average the midday volume mixing ratio of estragole exceeded that of toluene by almost a factor of two, the corresponding fluxes of these two compounds were nearly the same, amounting to 0.81 and 0.76 mg m−2 h−1, respectively. By fitting the canopy temperature and PAR response of the MEGAN emissions algorithm for isoprene and other emitted BVOCs a basal emission rate of isoprene of 7.8 mg m−2 h−1 was derived. We parameterise fluxes of depositing compounds using a resistance approach using direct canopy measurements of deposition. Consistent with Karl et al. (2010), we also propose that it is important to include deposition in flux models, especially for secondary oxidation products, in order to improve flux predictions.

In the past decade, we have witnessed rapid development of direct-injection mass spectrometric (DIMS) technologies that combine ever-improving mass and time resolution with high sensitivity and robustness. Here, we review some of the most significant DIMS technologies, which have been applied to rapid monitoring and quantification of volatile organic compounds (VOCs) and biogenic VOCS (BVOCs). They include MS-e-noses, atmospheric-pressure chemical ionization (APCI), proton-transfer-reaction mass spectrometry (PTR-MS), and selected ion-flow-tube mass spectrometry (SIFT-MS). DIMS-based MS-e-noses provide the possibility to screen large sample sets and may yield rich analytical information. APCI is a widespread ionization method and pioneered DIMS in environmental and flavor-release applications. SIFT-MS and PTR-MS allow better control of precursor-ion generation and hence of the ionization process. SIFT-MS puts the focus on control of the ionization process, while PTR-MS does so on sensitivity. Most (B)VOCs of interest can be efficiently detected and often identified by DIMS, thanks also to the possibility of switching between different precursor ions and the recent realization of time-of-flight-based equipments. Finally, we give selected examples of applications for each of the key technologies, including research in food-quality control (MS-e-nose), flavor release (APCI), environmental sciences (PTR-MS) and health sciences (SIFT-MS).

Norway spruce (Picea abies) is a strong emitter of biogenic volatile organic compounds (BVOCs). In the present study we investigated how shoot canopy position and high levels of stressors such as high temperature and ozone concentration, affect BVOC emission rates by means of in-situ and ex-situ experimental measurements. Therefore, BVOC emission from current-year spruce shoots was investigated under field and manipulated (temperature, ozone) laboratory conditions. Emitted BVOCs were sampled on desorption tubes, coupled with gas-exchange measurements of CO2 assimilation rate and stomatal conductance, and detected by gas chromatography coupled with mass spectrometry. Total BVOC emission rates from sun shoots under standard conditions were higher than those from shade shoots, although this was significant only in July, on the contrary, only α-pinene and γ-terpinene emission rates showed significant differences between sun and shade acclimated shoots in August. Limonene, α-pinene, β-pinene, and myrcene were identified as the most abundant BVOCs in both campaigns with emission rates above 0.2 nmol m−2 s−1. Ex-situ measurements revealed a significantly higher total BVOC emissions under high temperature level (40 °C) by ca. 175% as compared with standard temperature (30 °C), while a short-term fumigation of acute O3 concentration (200 ppb) had no effect on BVOC emissions and its spectrum. These findings might have a relevance considering the role of these compounds in protecting against oxidative stress and their possible stimulation in particular stressful conditions. Implication of such results into emission models may contribute to a more accurate estimation of BVOC emissions for Central European mountain regions dominated by Norway spruce forests and their rate under predicted climate change.

Biogenic volatile organic compounds (BVOC) emissions from bioenergy crops may differ from those of conventional crops. We compared emission rates of isoprene and a number of monoterpenes from the lignocellulosic bioenergy crops short-rotation coppice (SRC) willow and Miscanthus, with the conventional crops wheat and oilseed rape. BVOC emission rates were measured via dynamic vegetation enclosure and GC-MS analysis approximately monthly between April 2010 and August 2012 at a location in England and from SRC willow at two locations in Scotland. The largest BVOC emission rates were measured from willow in England and varied between years. Isoprene emission rates varied between

Biogenic Volatile Organic Compounds (BVOCs) are trace gases other than CO2 and CH4 produced and emitted by the biosphere, where the amounts released depend on climatic factors such as temperature and solar irradiation. However, interpretation of leaf-level measurements is currently hampered by factors such as large within-genotypic variability, measurement height and time in the season. A campaign was performed between June and August in 2013 in Taastrup, Denmark to study these uncertainties. BVOC emissions were measured from leaves and needles at heights of 2 m, 5.5m and 12.5m in the canopy and for seven trees; four Norway spruces (Picea abies) of which two trees had a budburst approximately a week before the other two, two English oaks (Quercus robur) and one European beech (Fagus sylvatica). Differences in chemical composition and emission strength between June and August were observed between the different trees. English oak's main compound isoprene increased from 62-74%of the total emission in June to approximately 97% in August, which is linked to leaf development over the summer season. The total emission from all measured spruce trees decreased from July to August, but without a loss in the diversity of emitted compounds. The trees showed indications of drought stress as there was a period without precipitation lasting 21 days during the study. There were no differences in emission patterns within all of the measured Norway spruces. For measurement height, there was only a significant difference in emission pattern for European beech as the top of the canopy emitted 7-9 times more in relation to lower canopy levels. Our results suggest there was little within-genotype variability and the wide spacing between trees had an influence on the individual emission patterns. These results are important in order to understand the significance of within-genotypic variation, canopy height and seasonal development in relation to the emission patterns of the selected species. Furthermore, it will provide helpful insights for modelers who wish to improve their emission estimates. (Less)

Biogenic volatile organic compounds (BVOCs), which are mainly emitted by vegetation, may create either positive or negative climate forcing feedbacks. In the Subarctic, BVOC emissions are highly responsive to temperature, but the effects of climatic warming on BVOC emissions have not been assessed in more extreme arctic ecosystems. The Arctic undergoes rapid climate change, with air temperatures increasing at twice the rate of the global mean. Also, the amount of winter precipitation is projected to increase in large areas of the Arctic, and it is unknown how winter snow depth affects BVOC emissions during summer. Here we examine the responses of BVOC emissions to experimental summer warming and winter snow addition - each treatment alone and in combination - in an arctic heath during two growing seasons. We observed a 280% increase relative to ambient in BVOC emissions in response to a 4°C summer warming. Snow addition had minor effects on growing season BVOC emissions after one winter but decreased BVOC emissions after the second winter. We also examined differences between canopy and air temperatures and found that the tundra canopy surface was on average 7.7°C and maximum 21.6°C warmer than air. This large difference suggests that the tundra surface temperature is an important driver for emissions of BVOCs, which are temperature dependent. Our results demonstrate a strong response of BVOC emissions to increasing temperatures in the Arctic, suggesting that emission rates will increase with climate warming and thereby feed back to regional climate change. (Less)

International audience; The effects of water deficit stress and plant water potential (w) on monoterpene and sesquiterpene leaf emissions from Rosmarinus officinalis, Pinus halepensis, Cistus albidus and Quercus coccifera were studied over 11 days of water withholding (from t 1 to t 11), after substrates had achieved their field capacity (control pots: t 0). Volatile compounds were sampled from the same twig per plant all throughout the study, using a dynamic bag enclosure system. Volatiles, collected in Tenax TA, were studied by means of GC-FID and GC-MS. Monoterpene emissions of water stressed plants (t 1 –t 11) were either similar to those of control seedlings (R. officinalis and Q. coccifera)or higher (P. halepensis and C. albidus). By contrast, sesquiterpene emissions were strongly reduced or inhibited after four days of water withholding, particularly for R. officinalis, thus altering terpene emission composition. Despite the positive effect of water stress on leaf monoterpene emissions of P. halepensis and C. albidus, the significant correlation between these emissions and w showed a slow decrease of these emissions over long term water deficit periods. This contrasted with the rapid decline of sesquiterpene emissions of R. officinalis according to lower values of w. These results provide an overall picture of the different responses of monoterpene and sesquiterpene emissions to progressive water loss. They also reveal the utility of using w for estimating some emission rates of some species according to drought conditions.

Emissions of biogenic volatile organic compounds (BVOC) by boreal evergreen trees have strong seasonality, with low emission rates during photosynthetically inactive winter and increasing rates towards summer. Yet, the regulation of this seasonality remains unclear. We measured in situ monoterpene emissions from Scots pine shoots during several spring periods and analysed their dynamics in connection with the spring recovery of photosynthesis. We found high emission peaks caused by enhanced monoterpene synthesis consistently during every spring period (monoterpene emission bursts, MEB). The timing of the MEBs varied relatively little between the spring periods. The timing of the MEBs showed good agreement with the photosynthetic spring recovery, which was studied with simultaneous measurements of chlorophyll fluorescence, CO 2 exchange and a simple, temperature history‐based proxy for state of photosynthetic acclimation, S. We conclude that the MEBs were related to the early stages of photosynthetic recovery, when the efficiency of photosynthetic carbon reactions is still low whereas the light harvesting machinery actively absorbs light energy. This suggests that the MEBs may serve a protective functional role for the foliage during this critical transitory state and that these high emission peaks may contribute to atmospheric chemistry in the boreal forest in springtime., Emissions of biogenic volatile organic compounds (BVOC) by boreal evergreen trees have strong seasonality. We measured high emission peaks from Scots pine shoots caused by enhanced monoterpene synthesis taking place simultaneously with the photosynthetic spring recovery. We conclude that the increased emissions were related to the photosynthetic recovery, when the efficiency of photosynthetic carbon reactions is low whereas the light harvesting machinery actively absorbs light energy. Increased emissions may serve a protective functional role for the foliage during the transitory state, and these high emission peaks may contribute to atmospheric chemistry in the boreal forest in springtime.

Biogenic volatile organic compound (BVOC) emissions are expected to change substantially because of the rapid advancement of climate change in the Arctic. BVOC emission changes can feed back both positively and negatively on climate warming. We investigated the effects of elevated temperature and shading on BVOC emissions from arctic plant species Empetrum hermaphroditum, Cassiope tetragona, Betula nana and Salix arctica. Measurements were performed in situ in long-term field experiments in subarctic and high Arctic using a dynamic enclosure system and collection of BVOCs into adsorbent cartridges analysed by gas chromatography-mass spectrometry. In order to assess whether the treatments had resulted in anatomical adaptations, we additionally examined leaf anatomy using light microscopy and scanning electron microscopy. Against expectations based on the known temperature and light-dependency of BVOC emissions, the emissions were barely affected by the treatments. In contrast, leaf anatomy of the studied plants was significantly altered in response to the treatments, and these responses appear to differ from species found at lower latitudes. We suggest that leaf anatomical acclimation may partially explain the lacking treatment effects on BVOC emissions at plant shoot-level. However, more studies are needed to unravel why BVOC emission responses in arctic plants differ from temperate species.

The aim of this paper was to provide an overview of the current state of the art on research into the emission of biogenic volatile organic compounds (BVOCs) from vegetation fires. Significant amounts of VOCs are emitted from vegetation fires, including several reactive compounds, the majority belonging to the isoprenoid family, which rapidly disappear in the plume to yield pollutants such as secondary organic aerosol and ozone. This makes determination of fire-induced BVOC emission difficult, particularly in areas where the ratio between VOCs and anthropogenic NOx is favourable to the production of ozone, such as Mediterranean areas and highly anthropic temperate (and fire-prone) regions of the Earth. Fire emissions affecting relatively pristine areas, such as the Amazon and the African savannah, are representative of emissions of undisturbed plant communities. We also examined expected BVOC emissions at different stages of fire development and combustion, from drying to flaming, and from heatwaves coming into contact with unburned vegetation at the edge of fires. We conclude that forest fires may dramatically change emission factors and the profile of emitted BVOCs, thereby influencing the chemistry and physics of the atmosphere, the physiology of plants and the evolution of plant communities within the ecosystem. © 2014 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.

Mixing ratios and fluxes of volatile organic compounds (VOCs) were measured by PTR-MS (and GC–MS) and virtual disjunct eddy covariance during a three-week field campaign in summer 2009 within and above a Douglas fir ( Pseudotsuga menziesii ) forest in Speulderbos, the Netherlands. Measurements included the first non-terpenoid species fluxes and mixing ratios for Douglas fir canopy. Above-canopy emissions of monoterpenes were comparable to previous studies of P. menziesii , with estimated standard emission factors for the first and second halves of the campaign of 0.8 ± 0.4 and 0.8 ± 0.3 μg g dw −1 h −1 , and temperature coefficients of 0.19 ± 0.06 and 0.08 ± 0.05 °C −1 , respectively. Estimated isoprene standard emission factors for the two halves of the campaign were 0.09 ± 0.12 and 0.16 ± 0.18 μg g dw −1 h −1 . Fluxes of several non-terpenoid VOCs were significant, with maximum fluxes greater than has been measured for other coniferous species. α-Pinene was the dominant monoterpene within and above the canopy. Within-canopy mixing ratios of individual species were generally greatest in early evening consistent with reduced vertical mixing and continued temperature-dependent emissions. Acetaldehyde, acetone and monoterpenes had elevated mixing ratios toward the bottom of the canopy (5–10 m) with assumed contribution from the large quantities of forest-floor leaf litter. MBO (2-methyl-3-buten-2-ol) and estragole had peak mixing ratios at the top of the canopy and are known to have coniferous sources. MVK + MACR (methyl vinyl ketone and methacrolein) also had highest mixing ratios at the top of the canopy consistent with formation from in-canopy oxidation of isoprene. The work highlights the importance of quantifying a wider variety of VOCs from biogenic sources than isoprene and monoterpenes.

The depletion of fossil fuel resources, pollution concerns and the challenge of energy security are driving the search for renewable energy sources. The use of lignocellulosic plant biomass as an energy source is increasing in the United Kingdom and worldwide. In the UK, up to 0.35MHa (6% of total arable land) may be planted with perennial bioenergy crops by 2020 in order to meet renewable energy and CO2 reduction targets. Several plant species that produce high biomass from low inputs have been identified. The most promising for the UK climate are the genus Miscanthus, a perennial rhizomatous grass which can grow up to 3.5m in a year, and short rotation coppice (SRC) willow (Salix spp.), plantations of which can remain viable for up to 30 years. Although bioenergy crops are perceived as “carbon neutral”, changes in land use can have a wider impact on atmospheric composition than through CO2 alone. This study compares vegetation fluxes of methyl halides (CH3Br and CH3Cl) and biogenic volatile organic compounds (BVOCs) from perennial bioenergy crops and annual arable crops at three sites in the UK. Methyl halides are the most abundant natural vectors of bromine and chlorine into the stratosphere and play an important role in stratospheric ozone destruction. BVOCs affect atmospheric oxidising capacity and are a major precursor to the formation of ozone and secondary organic aerosols in the troposphere. Although terrestrial vegetation is an important source of these trace gases there are very few previous measurements of these reactive gases from bioenergy crops. This study describes measurements conducted at two SRC willow sites in Scotland, and one site in England planted with adjacent perennial bioenergy crops and annual arable crops, to quantify and characterise natural methyl halide and BVOC fluxes from vegetation. Measurements were conducted with branch chambers, using static enclosure techniques to measure methyl halide fluxes and dynamic enclosures to measure BVOCs such as isoprene and -pinene. Fluxes were calculated from the concentration difference between background/inlet samples and after enclosure/outlet samples. Methyl halide concentrations were determined by sampling gas from static enclosures followed by analysis using an oxygen-doped GC-ECD with a custom-built pre-concentration unit. Samples for BVOC analysis were collected onto adsorbent tubes and a thermal desorption GC-MS was used to determine BVOC concentrations. Potentially influential environmental variables such as photosynthetically active radiation (PAR), total solar radiation, air temperature, soil temperature, internal chamber temperature and soil moisture were recorded in parallel to the enclosures to determine their potential relationships to fluxes. Long-term environmental data was also available from on-site or nearby weather stations. Long-term measurements were carried out for 2 1 2 years at a site in Lincolnshire, England where adjacent fields are planted with Miscanthus, SRC willow and annual arable crops (wheat and oilseed rape crop rotation). Vegetation measurements were made almost every month throughout the period, with more intensive measurements such as full diurnal cycle carried out during the summer. Ten sampling points are sampled in each field and semi-diurnal measurements are taken regularly. Long-term measurements were also carried out at two sites in Scotland planted with SRC willow, one in Arnot, Perth & Kinross which was sampled for a year and one in East Grange, Fife which was sampled for half a year. Up to 30 sampling points were employed in Arnot and another 10 in East Grange. The bioenergy crops and wheat emitted low fluxes of methyl halides in comparison to the oilseed rape. Mean annual net fluxes of CH3Br and CH3Cl from Miscanthus were 1.8 ng g (dry weight)-1 h-1 and 11 ng g-1 h-1, respectively. At the three willow sites, mean annual net fluxes of CH3Br and CH3Cl ranged between 0.6 - 1.7 ng g-1 h-1, and 1.7 - 12 ng g-1 h-1, respectively. Negligible fluxes of methyl halides were measured from wheat but oilseed rape was found to emit large fluxes of methyl halides with mean annual net fluxes of CH3Br and CH3Cl of 20 ng g-1 h-1and 144 ng g-1 h-1, respectively. The largest BVOC fluxes were measured from SRC willow at the Brattleby site, with high mean annual net fluxes of isoprene (77 μ g g-1 h-1), α -pinene (46 g μg-1 h-1), β -pinene (5.5 μ g g-1 h-1), limonene (3.7 μ g g-1 h-1) and δ -3-carene (11 μ g g-1 h-1). However, mean annual net BVOC fluxes measured at Arnot and East Grange were much lower. High fluxes of - pinene were measured from Miscanthus in 2010 (giving a mean annual net flux of 65 μ g g-1 h-1) but no other significant BVOC fluxes were distinguished. Negligible fluxes of isoprene were measured from wheat but fluxes of monoterpenes were high with mean annual net fluxes of 65 μ g g-1 h-1 and 25 μg g-1 h-1 for α -pinene and limonene, respectively. No significant fluxes of BVOCs were measured from the oilseed rape. All fluxes demonstrated a strong seasonal trend with higher emissions during the summer growing season and low to zero emissions over winter. The high spatial variability was captured by sampling from many points in each field. Some diurnal measurements exhibited a clear pattern of higher emissions during the day and low to zero emissions at night. Some positive correlations between fluxes and environmental variables such as PAR and air temperature were observed. An experiment carried out on willow cuttings in the greenhouse found no clear increase or decrease in fluxes of BVOCs in response to N fertiliser treatment, instead fluxes were found to vary significantly with some of the observed environmental variables. UK estimates were derived by extrapolating measured fluxes using the current respective land cover areas for Miscanthus and SRC willow. Estimated UK annual fluxes of CH3Br and CH3Cl from Miscanthus were 0.01Mgy-1 and 0.05Mgy-1, respectively and from SRC willow were 0.06Mgy-1 and 0.4Mgy-1, respectively, accounting for a very small percentage of total global annual turnover of CH3Br and CH3Cl. Estimated UK annual fluxes of the BVOCs isoprene and α -pinene from Miscanthus were 0.01Mgy-1 and 0.4Mgy-1, respectively and from SRC willow were 3Mgy-1 and 1Mgy-1, respectively. Future planting of SRC willow to meet the UKs energy needs could lead to a potential annual isoprene flux of 150 MgMgy-1.

Biogenic volatile organic compounds (BVOC) are a wide-ranging group of trace gas components in the atmosphere which are emitted naturally from Earth’s surface. It is now recognised that biogenically sourced VOCs are far more significant on a global scale than those from anthropogenic sources, with up to 10 times greater emissions. Very few field-based studies of fluxes from plant canopies have been undertaken, particularly for non-terpenoid compounds. This thesis presents mixing ratio and flux measurements of BVOC from a range of temperate plant canopies: Douglas fir, short-rotation coppice willow, Miscanthus and mixed peatland vegetation. The virtual disjunct eddy covariance technique (vDEC) using a proton transfer reaction mass spectrometer (PTR-MS) as a fast VOC sensor was used for all measurements except for peatlands, where grab samples were collected on adsorbent sampling tubes for later chromatographic analysis. The PTR-MS was also utilised for measuring the rate of degradation of VOCs during laboratory chamber experiments. Mixing ratios and fluxes of VOCs measured within and above a Douglas fir forest were the first canopy-scale measurements for this species. Fluxes of monoterpenes were comparable to previous studies while isoprene was also detected (standard emissions factors up to 1.15 μg gdw -1 h-1 and 0.18 μg gdw -1 h-1, respectively). Emissions of oxygenated VOCs were also found to be significant, highlighting the importance of quantifying a wider variety of VOCs from biogenic sources, other than isoprene and monoterpenes. Results for bioenergy crops Miscanthus and willow showed that willow was a high isoprene emitter (20 μg gdw -1 h-1), but no measureable VOCs were detected from Miscanthus. This indicates that future expansion of bioenergy crops, and hence species selection, should take resultant air quality and human health impacts – due to changing VOC emissions – into account. Fluxes of BVOC from a Scottish peatland are the first reported measurements for this ecosystem in a temperate climate. Additionally, to assess the impact of nitrogen deposition on VOC fluxes, BVOC measurements were taken from sample plots in a pre-existing, long-term field manipulation study to assess impacts of wet nitrate or ammonium deposition on peatland. The peatland was found to be a significant source of isoprene and monoterpenes (590 and 1.5 μg m-2 h-1 respectively) and there was evidence that emissions were affected by wet nitrogen treatment. Isoprene emissions were reduced by both nitrate and ammonium treatment, while nitrate increased β- pinene fluxes. Increasing atmospheric nitrogen concentrations are therefore predicted to have an impact on VOC emission. Chamber studies showed that the rate of loss of α-pinene from the gas-phase during oxidation – and hence potential formation of secondary organic aerosol (SOA) – decreased with increasing isoprene mixing ratio. This was not observed for limonene. These results show that as isoprene mixing ratios increase with increasing global temperatures, negative feedback on radiative forcing from SOA particles may be suppressed. Results from this thesis provide valuable experimental data for a range of temperate plant canopies, which will help constrain modelled predictions of future VOC emissions. Additionally, the importance of understanding the effects of land use and environmental change on VOC emissions was demonstrated.

Volatile Organic Compounds (VOC) play an important role in atmospheric chemistry and are involved in the formation of secondary atmospheric pollutants as ozone and organic aerosols. Biogenic emissions of volatile organic compounds are tenfold greater than anthropogenic emissions on a global scale but their characterization remains uncertain regionally. Advances in atmospheric chemistry modeling rely on better emission inventory which needs in situ flux measurement. This work focuses on biogenic VOC emissions from Mediterranean vegetation in the frame of ChArMEx (Chemistry and Aerosol Mediterranean Experiment) that aims to concentrate scientific effort to study atmospheric chemistry and aerosols in the Mediterranean region. The Eddy Covariance (EC) method allows direct measurement of trace gas exchange between the surface and the atmosphere. EC is a reference method for flux measurement but is adapted to only a limited number of trace gas species because it requires simultaneous fast measurement (~ 0.1 s) of the species concentration and vertical wind speed. In order to broaden the range of applicability of this method, several other methods derived from EC have been proposed. Among these, the Disjunct Eddy Covariance (DEC) method relaxes the constraint on fast concentration measurement while preserving good accuracy on the flux calculation. In the frame of this PhD work, a sampling system dedicated to the DEC method for VOC flux measurement was developed. This device called MEDEE (Mesures par Échantillonnage Disjoint des Échanges d'Espèces en trace) relies on a novel technology that allows the rapid capture of an air parcel and insures its transfer at a constant pressure towards an on-line analyzer. It is composed of two mechanical syringes moved by electric actuators with an alternated functioning to supply continuously the analyzer. Three solenoid valves are installed on each reservoir to drive the sample flow depending on the cycle. A micro controller chip is used to give the rhythm of the whole system with millisecond accuracy. This sampling system has been built in chemically inert materials to avoid sample contamination or destruction; this makes MEDEE fully compatible with reactive species. MEDEE has been tested and validated on ground and aboard an aircraft, during two field campaigns. It was coupled to a fast isoprene sensor for BVOC flux measurements during two field campaigns in summers 2010 and 2011 above a downy oak forest. A Neural Network (NN) approach has been used to derive a biogenic VOC emission algorithm from these canopy level measured fluxes and concurrent environmental parameters. Isoprene emission modeling has been validated for the observed environmental conditions. In the future, such emission parameterization will be implemented in a coupled chemistry-dynamics model to study the impact of biogenic VOC emissions on air quality; Les Composés Organiques Volatils (COV) jouent un rôle important dans la chimie de l'atmosphère et participent à la formation de polluants secondaires comme l'ozone et les aérosols organiques. Les émissions biogéniques de COV dominent d'un facteur dix les émissions anthropiques à l'échelle globale mais leur caractérisation à l'échelle régionale est incertaine. Les progrès en modélisation de la chimie atmosphérique passent par l'amélioration des inventaires d'émissions, ce qui nécessite des mesures de flux in situ. Ces travaux portent sur l'étude des émissions de COV biogéniques par les végétations méditerranéennes dans le cadre du programme ChArMEx (Chemistry and Aerosol Mediterranean Experiment) qui vise à concentrer les efforts scientifiques sur l'étude de la chimie et des aérosols de l'atmosphère du bassin méditerranéen. La méthode Eddy Covariance (EC) permet de quantifier directement les échanges d'espèces chimiques entre la surface et l'atmosphère. Cette méthode constitue une référence pour les mesures de flux mais n'est applicable qu'à un nombre limité d'espèces car elle requiert la mesure rapide (~ 0,1 s) et simultanée de la concentration du composé étudié ainsi que de la vitesse du vent vertical. Afin d'élargir le champ de mise en œuvre de cette technique d'autres solutions dérivées de l'EC ont été proposées, dont la méthode Disjunct Eddy Covariance (DEC) qui a pour particularité de réduire la contrainte sur la mesure rapide de l'espèce chimique tout en gardant une précision acceptable sur le calcul du flux. Dans le cadre de ces travaux de thèse un système de prélèvement a été développé pour mettre en œuvre la mesure de flux de COV par la méthode DEC. Ce dispositif appelé MEDEE (Mesures par Échantillonnage Disjoint des Échanges d'Espèces en trace) repose sur une technologie nouvelle qui permet une capture rapide d'un échantillon d'air et assure son transfert à pression constante vers un analyseur connecté en ligne. Il est composé de deux "seringues mécaniques" actionnées par des vérins électriques dont le fonctionnement est alterné pour alimenter en continu l'analyseur. Trois électrovannes disposées à l'entrée de chaque réservoir dirigent le flux d'air en fonction du cycle de fonctionnement. L'ensemble du système est cadencé par un microcontrôleur avec une précision à la milliseconde. Le système de prélèvement a été réalisé en matériaux inertes chimiquement pour éviter la dégradation de l'échantillon et être compatible avec les espèces en trace réactives. MEDEE a été testé et validé pour les mesures de flux au sol et en avion lors de deux campagnes de terrain. Le système MEDEE a ainsi permis, lors de deux campagnes de mesures pendant les étés 2010 et 2011 au-dessus d'une forêt de chênes pubescents, de mesurer les flux d'isoprène grâce à un couplage avec un analyseur adapté (Fast Isoprene Sensor). Un réseau de neurones artificiels (RNA) a ensuite été utilisé pour déterminer une paramétrisation des flux d'isoprène en fonction des paramètres environnementaux à partir des observations des campagnes de mesures. La modélisation des émissions d'isoprène a été validée pour les conditions environnementales rencontrées. Cette paramétrisation servira dans un modèle de chimie atmosphérique à l'étude de l'impact des émissions de COV biogéniques sur la qualité de l'air.

Volatile Organic Compounds (VOC) play an important role in atmospheric chemistry and are involved in the formation of secondary atmospheric pollutants as ozone and organic aerosols. Biogenic emissions of volatile organic compounds are tenfold greater than anthropogenic emissions on a global scale but their characterization remains uncertain regionally. Advances in atmospheric chemistry modeling rely on better emission inventory which needs in situ flux measurement. This work focuses on biogenic VOC emissions from Mediterranean vegetation in the frame of ChArMEx (Chemistry and Aerosol Mediterranean Experiment) that aims to concentrate scientific effort to study atmospheric chemistry and aerosols in the Mediterranean region. The Eddy Covariance (EC) method allows direct measurement of trace gas exchange between the surface and the atmosphere. EC is a reference method for flux measurement but is adapted to only a limited number of trace gas species because it requires simultaneous fast measurement (~ 0.1 s) of the species concentration and vertical wind speed. In order to broaden the range of applicability of this method, several other methods derived from EC have been proposed. Among these, the Disjunct Eddy Covariance (DEC) method relaxes the constraint on fast concentration measurement while preserving good accuracy on the flux calculation. In the frame of this PhD work, a sampling system dedicated to the DEC method for VOC flux measurement was developed. This device called MEDEE (Mesures par Échantillonnage Disjoint des Échanges d'Espèces en trace) relies on a novel technology that allows the rapid capture of an air parcel and insures its transfer at a constant pressure towards an on-line analyzer. It is composed of two mechanical syringes moved by electric actuators with an alternated functioning to supply continuously the analyzer. Three solenoid valves are installed on each reservoir to drive the sample flow depending on the cycle. A micro controller chip is used to give the rhythm of the whole system with millisecond accuracy. This sampling system has been built in chemically inert materials to avoid sample contamination or destruction; this makes MEDEE fully compatible with reactive species. MEDEE has been tested and validated on ground and aboard an aircraft, during two field campaigns. It was coupled to a fast isoprene sensor for BVOC flux measurements during two field campaigns in summers 2010 and 2011 above a downy oak forest. A Neural Network (NN) approach has been used to derive a biogenic VOC emission algorithm from these canopy level measured fluxes and concurrent environmental parameters. Isoprene emission modeling has been validated for the observed environmental conditions. In the future, such emission parameterization will be implemented in a coupled chemistry-dynamics model to study the impact of biogenic VOC emissions on air quality; Les Composés Organiques Volatils (COV) jouent un rôle important dans la chimie de l'atmosphère et participent à la formation de polluants secondaires comme l'ozone et les aérosols organiques. Les émissions biogéniques de COV dominent d'un facteur dix les émissions anthropiques à l'échelle globale mais leur caractérisation à l'échelle régionale est incertaine. Les progrès en modélisation de la chimie atmosphérique passent par l'amélioration des inventaires d'émissions, ce qui nécessite des mesures de flux in situ. Ces travaux portent sur l'étude des émissions de COV biogéniques par les végétations méditerranéennes dans le cadre du programme ChArMEx (Chemistry and Aerosol Mediterranean Experiment) qui vise à concentrer les efforts scientifiques sur l'étude de la chimie et des aérosols de l'atmosphère du bassin méditerranéen. La méthode Eddy Covariance (EC) permet de quantifier directement les échanges d'espèces chimiques entre la surface et l'atmosphère. Cette méthode constitue une référence pour les mesures de flux mais n'est applicable qu'à un nombre limité d'espèces car elle requiert la mesure rapide (~ 0,1 s) et simultanée de la concentration du composé étudié ainsi que de la vitesse du vent vertical. Afin d'élargir le champ de mise en œuvre de cette technique d'autres solutions dérivées de l'EC ont été proposées, dont la méthode Disjunct Eddy Covariance (DEC) qui a pour particularité de réduire la contrainte sur la mesure rapide de l'espèce chimique tout en gardant une précision acceptable sur le calcul du flux. Dans le cadre de ces travaux de thèse un système de prélèvement a été développé pour mettre en œuvre la mesure de flux de COV par la méthode DEC. Ce dispositif appelé MEDEE (Mesures par Échantillonnage Disjoint des Échanges d'Espèces en trace) repose sur une technologie nouvelle qui permet une capture rapide d'un échantillon d'air et assure son transfert à pression constante vers un analyseur connecté en ligne. Il est composé de deux "seringues mécaniques" actionnées par des vérins électriques dont le fonctionnement est alterné pour alimenter en continu l'analyseur. Trois électrovannes disposées à l'entrée de chaque réservoir dirigent le flux d'air en fonction du cycle de fonctionnement. L'ensemble du système est cadencé par un microcontrôleur avec une précision à la milliseconde. Le système de prélèvement a été réalisé en matériaux inertes chimiquement pour éviter la dégradation de l'échantillon et être compatible avec les espèces en trace réactives. MEDEE a été testé et validé pour les mesures de flux au sol et en avion lors de deux campagnes de terrain. Le système MEDEE a ainsi permis, lors de deux campagnes de mesures pendant les étés 2010 et 2011 au-dessus d'une forêt de chênes pubescents, de mesurer les flux d'isoprène grâce à un couplage avec un analyseur adapté (Fast Isoprene Sensor). Un réseau de neurones artificiels (RNA) a ensuite été utilisé pour déterminer une paramétrisation des flux d'isoprène en fonction des paramètres environnementaux à partir des observations des campagnes de mesures. La modélisation des émissions d'isoprène a été validée pour les conditions environnementales rencontrées. Cette paramétrisation servira dans un modèle de chimie atmosphérique à l'étude de l'impact des émissions de COV biogéniques sur la qualité de l'air.