We invite contributions on plant and other biogenic VOC emissions sources (e.g., from soil, litter, and freshwater) under environmental changes and welcome contributions on methodological advances in sampling and analysis techniques, and modelling frameworks that bridge experimental observations with atmospheric processes.
Leaves must sustain high rates of photosynthesis to support growth while avoiding over-reduction of the chloroplast electron transport chain and the formation of damaging reactive oxygen species during daily exposure to high light and temperature. This challenge is particularly acute for C₃ species such as Holcus lanatus, which experience high rates of photorespiration under the warm, high-light conditions typical of grassland ecosystems.
In leaves of H. lanatus at the Point Reyes Field Station (California, USA), we observed a pronounced midday decline (approximately ten-fold) in the quantum efficiency of photosystem II (ΦPSII) despite elevated electron transport rates (ETR), temperature, and incident light, followed by full recovery in the evening. Controlled light- and temperature-response experiments revealed that net CO₂ assimilation, ETR, and volatile organic compound (VOC) emissions remained tightly coupled during periods of ΦPSII suppression, indicating sustained biosynthetic activity even as photochemical efficiency declined.
Among emitted VOCs, methyl salicylate (MeSA) and cis-β-ocimene—derived from the shikimate and isoprenoid pathways and linked to the Calvin–Benson cycle through carbon skeleton supply—showed strong light and temperature responsiveness. In contrast, α-pinene and sabinene emissions were largely light-independent and negatively temperature-sensitive. Given their established roles as potent phytohormones, these observations raise the possibility that photosynthesis-derived compounds such as MeSA and cis-β-ocimene act as internal feedback signals regulating the photosynthetic light reactions.
Although trans-β-ocimene is widely regarded as the dominant isomer in plant emissions, particularly under biotic stress, our sequence analysis predicts that approximately 18% of β-ocimene-producing species possess a cis-β-ocimene synthase, including a validated plastid-localized example in Cannabis sativa. By comparison, UniProt currently annotates cis-β-ocimene synthases in only ~7% of species. Together, these findings suggest three paradigm shifts: (i) photosynthetic products such as MeSA may directly regulate light reactions; (ii) MeSA may stimulate β-ocimene production, enhancing thermoprotection of photosynthesis; and (iii) cis-β-ocimene is likely far more abundant in nature than previously assumed. This dynamic decoupling of ΦPSII from electron transport, CO₂ assimilation, and biosynthesis under thermal and light stress has important implications for photosynthesis modeling and the interpretation of solar-induced fluorescence.
How to cite: Jardine, K., Elliott, A., Seubert, H., Kosina, S., Pegoraro, E., Crutchfield-Peters, K., Brown, E., Grasberger, E., Benson, S., and Torn, M.: Light and High Temperature Dependent Decline in Photosystem II Efficiency in Holcus Is Associated with Photoprotective Roles of Volatile Signals Methyl Salicylate and cis-β-Ocimene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22882, https://doi.org/10.5194/egusphere-egu26-22882, 2026.
Biogenic Volatile Organic Compound (BVOC) emissions account for more than 70% of VOC global emissions and play a significant role in atmospheric chemistry due to their high reactivity. These compounds are naturally emitted by trees as they are involved in ecological processes such as plant communication and defense against biotic and abiotic stressors. However, climate change has increased those stress factors for trees, altering both magnitude and composition of BVOC emissions. Once oxidized in the atmosphere, BVOCs contribute to the production of Secondary Organic Aerosols (SOA) which are involved in cloud formation, mitigating the Earth’s radiative balance and impacting air quality. Investigating how emission rates and compositions are impacted by such stressors is essential in understanding how atmospheric chemistry is affected.
So far, most studies focused on coniferous trees and isolated stress factors, leaving broad-leaved trees and combined stress impacts understudied, although common. To address the gap, this study sheds light on the BVOC emissions from two common deciduous tree species in Europe: English oak (Quercus Robur), an isoprene emitter, and European beech (Fagus Sylvatica), a monoterpene emitter. They were successively exposed to herbivory feeding of gypsy moth larvae (Lymantria Dispar Dispar) then both herbivory and heat stress (up to ~40°C).
To quantify BVOC fluxes, the emissions were sampled from a climate-controlled plant-chamber (SAPHIR-PLUS) by PTR-TOF-MS coupled to a fastGC. Temperature ramp experiments were conducted under each condition to study the temperature sensitivity of terpenoid emissions in response to the different stressors.
Here, we present results from an intensive two-month campaign with focus on the main primary BVOC emissions. Preliminary results indicate that herbivory feeding increased monoterpenes emissions, but heat stress induced a stronger burst in emissions for both tree species, highlighting their role in plant defense response.
How to cite: Depp, C., Dey, B., Gu, Y., Novelli, A., Hohaus, T., and Pfannerstill, E.: Stress is in the air: BVOC emissions from beech and oak trees under combined heat stress and herbivory feeding, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5389, https://doi.org/10.5194/egusphere-egu26-5389, 2026.
Climate change is increasing the frequency and severity of Amazonian droughts, and El Niño events are predicted to become more intense and persistent. Despite this, the effects of drought on biogenic volatile organic compound (BVOC) emissions from tropical rainforests remain poorly understood. Chiral BVOCs like alpha-pinene, exist as mirror image pairs, known as enantiomers. Enantiomers have the same atmospheric reactivity, but are produced and emitted by different enzymes and internal leaf mechanisms. Abiotic stress can alter their relative emissions, suggesting enantiomer ratios could indicate stress severity. Here we present ambient concentrations from within the Amazon rainforest canopy of methyl salicylate, isoprene, monoterpenoids, and sesquiterpenoids from the Amazon rainforest spanning the 2023–2024 El Niño, the most severe drought ever recorded in the basin. Correlations between alpha-pinene enantiomers shifted with stress, aligning with weakening carbon dioxide uptake by vegetation and transition between de novo and storage emissions. Low- and high-stress zones, along with a recovery zone, were defined through alpha-pinene enantiomer correlations, revealing a metric for ecosystem stress. Isoprene and total monoterpenoid abundances showed little influence from El Niño, while total sesquiterpenoids increased by 122% across the El Niño duration. Unexpected emissions of lower-volatility sesquiterpene alcohols, including beta-eudesmol, alpha-eudesmol, and gamma-eudesmol, occurred during the wet season following the peak drought revealing an adaptation to adverse conditions linked to oxidative stress defence. Our results show how severe drought drives shifts in enantiomer ratios and isoprenoid composition in the atmosphere, reflecting underlying physiological changes as vegetation responds to abiotic stress.
How to cite: Byron, J., Pugliese, G., de A. Monteiro, C., Robin, M., Gomes Alves, E., Schuettler, J., Hartmann, S. C., Edtbauer, A., Krumm, B., Zannoni, N., Hall, D., Tsokankunku, A., Q. Dias-Junior, C., A. Quesada, C., Harder, H., Bourtsoukidis, E., Lelieveld, J., and Williams, J.: Mirror image molecules and low volatility organic compounds emissions expose state ofrainforest stress, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11544, https://doi.org/10.5194/egusphere-egu26-11544, 2026.
The main sources of volatile organic compounds (VOCs) emitted from forest soils are roots and soil microorganisms. However, quantifying the relative contributions of these sources to net soil VOC emissions and the proportion of root VOCs degraded by soil microorganisms is challenging.
In order to partition soil VOC emissions into root and microbial VOC emissions, we conducted a controlled mesocosm experiment using Picea abies and Fagus sylvatica saplings, as well as soil (Cambisol) collected from a temperate forest dominated by these two species. VOC emissions from the soil surface (combined root and soil emissions), as well as from excavated roots and root-free bulk soil (sieved to 2 mm), were analyzed using PTR-TOF-MS and GC-MS. To evaluate the role of microorganisms as a source or sink of VOCs in the rhizosphere, microbial colonization of roots was modified by applying three washing treatments: (1) no washing (intact rhizosphere, high colonization), (2) water washing (partial removal of root microbiome, intermediate colonization), and (3) washing with 70% (v/v) ethanol (disinfection, reduced colonization), with 6 replicates per species and treatment.
This study aims to improve our understanding of the soil VOC fluxes in forest ecosystems by quantifying the contributions of roots and microorganisms to net soil VOC emissions, as well as the uptake of root VOCs by soil microorganisms.
How to cite: Meischner, M., Steuerle, A., Rinnan, R., and Werner, C.: Untangling root and microbial volatile organic compound emissions from soils of two different temperate tree species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1778, https://doi.org/10.5194/egusphere-egu26-1778, 2026.
Biogenic volatile organic compounds (VOCs) significantly influence atmospheric chemistry, yet the importance of microbial VOC emissions remains understudied. We investigate petrichor VOC emissions, the characteristic scent following rainfall after prolonged drought, across Israel’s aridity gradient, by simulating soil rewetting events. Rewetting triggered strong VOC fluxes (1-3.5 nmol m-2 s-1 ground area) dominated by sesquiterpenes and benzenoids, with emission patterns linked to climate-regions, soil aridity, and microbial community composition. Petrichor was composed of a complex bouquet of 58 VOCs, and the initial VOC burst resembled the CO2 pulse of the Birch effect. Petrichor emissions showed ozone and secondary organic aerosol formation potentials comparable to anthropogenic VOC sources in Israel. Despite compositional differences, emission magnitudes were of similar order across the aridity gradient. Given that drylands cover nearly half of Earth's land and are expanding, these episodic microbial VOC emissions may represent a significant, previously overlooked source of reactive carbon with potential implications for regional and global atmospheric chemistry.
How to cite: Ghirardo, A., Poodiack, B., Siebner, H., Jaffe, M. K., Weber, B., Schnitzler, J.-P., Bonkowski, M., Gillor, O., and Guenther, A. B.: Dryland soil rewetting induces strong VOC emissions with potential to form ozone and aerosol, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21725, https://doi.org/10.5194/egusphere-egu26-21725, 2026.
The composition of cave atmospheres is unknown beyond ventilation studies on carbon dioxide (CO2) and methane (CH4). The identities, concentrations, and roles of volatile organic compounds (VOCs) and their link to CO2 and CH4 – although crucial for understanding subterranean carbon cycling – remains unexplored. Caves also take part in gas exchange with terrestrial ecosystems and the atmosphere, acting as sources and sinks of reactive gases. However, the magnitude of this gas exchange, and the potential effects on local and global carbon budgets, has not yet been characterized.
We analyzed VOCs, CO2, CH4, and oxygen in situ from the air of two caves (in Loulé and Torres Novas) in the main karst massifs of Portugal, along with cave microbiomes in sediment samples. Additionally, we isolated bacterial and fungal species from the sediment samples and investigated their volatile fingerprints in vitro. We used headspace vials and sorbent tubes for the in situ and in vitro volatile sampling combined with analysis via mass spectrometric and optical spectroscopy methods. Cave microbial compositions were analyzed with metabarcoding of 16S rRNA (bacteria) and ITS (fungi) genes.
We will present novel data connecting cave atmospheric compositions to cave microbial carbon cycling, including analysis of the origin of volatiles through stable isotope analysis (13C). We also present data for seasonal and spatial variation in the cave atmospheric compositions. Our results suggest that cave atmospheres are dynamic rather than stable, affected by outside conditions, and therefore, potentially compromised by climate change. Conversely, we confirm that caves can act as sources and sinks for some reactive gases, suggesting that they can also impact the surrounding environment.
How to cite: Roslund, K., Reboleira, A. S., Bodawatta, K., Civa, L., Sommer, A., Poulsen, M., and Rinnan, R.: Volatile compounds in cave ecosystems and their roles in subterranean carbon cycling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4871, https://doi.org/10.5194/egusphere-egu26-4871, 2026.
Volatile organic compounds (VOCs) are diverse bioactive molecules of low molecular weight and high vapor pressure. VOCs are produced by biotic and abiotic processes and are important for atmospheric chemistry as main biogenic precursors of secondary organic aerosols. In marine environments, the phytoplankton are the main source of marine VOCs, which appear to be an important source of organic compounds fueling bacterioplankton growth. Increased eutrophication and rising temperatures will likely increase intensity of coastal phytoplankton blooms in the coming decades with the potential cascading consequence of elevated VOC production rates and emissions. To assess VOC production by a phytoplankton bloom, we conducted a mesocosm experiment where VOC production by natural, unaltered microbial communities were compared to that by a phytoplankton bloom induced by nutrient amendment. VOCs were measured by combining a purge-and-trap system with a high-sensitivity proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). Using 16S rRNA and 18S rRNA sequencing data, we analyzed the prokaryote and eukaryote community composition and the effect of their relationships on the VOC composition and concentration. The concentration and composition of VOCs changed over the course of the phytoplankton bloom, and some VOCs were significantly higher in the phytoplankton bloom than in the unaltered microbial communities. A strong and significant correlation was found between the bacterial and eukaryotic communities, and VOCs. In addition, permutation analysis showed how the relationships between phytoplankton and bacteria can modify the composition of VOCs. These results evidence the effect of phytoplankton-bacteria relationships in marine VOC emissions.
How to cite: Costas Selas, C., Foroughan, M., Som, S., Galen, E., Martin, J. D., Helberg, A., Rohard, S., Termansen, K. L., Rinnan, R., and Riemann, L.: Impact of phytoplankton blooms on marine VOCs emission , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17178, https://doi.org/10.5194/egusphere-egu26-17178, 2026.
As climate warming is expected to extend the growing season and enhance vegetation productivity in the Arctic, a consequent increase in emissions of Biogenic Volatile Organic Compounds (BVOC) is forecasted.
Isoprenoid emissions are known to be driven, among other factors, by photosynthetic processes. Our hypothesis is then that the emissions of particularly isoprenoids can be linked to remotely sensed proxies of photosynthetic activity in typical vegetation of low Arctic tundra.
We tested this hypothesis by examining the relationship between Solar-Induced chlorophyll Fluorescence (SIF) in the O2-A absorption band and BVOC emission rates in a field spectroscopy framework, to further investigate the relationship between the reflectance properties of vegetation and total BVOC/isoprenoid emission rates. The study site is located in the area of Kobbefjord, Greenland.
The results of our analysis demonstrate that SIF and other spectral indices (Enhanced Vegetation Index – EVI, Photochemical Reflectance Index – PRI, MERIS Terrestrial Chlorophyll Index – MTCI) explain a substantial share of the variation in isoprenoid and total BVOC emissions. These findings can potentially be of aid in opening new avenues to model BVOC emissions at larger scales, as SIF and other relevant indices can be directly derived from new-generation UAV and satellite imagery.
How to cite: Grillini, F., Laursen, S. N., Smart, A., Wang, P., Feng, S., Bendig, J., and Westergaard-Nielsen, A.: Links between Solar-Induced chlorophyll Fluorescence and isoprenoid emissions from field spectroscopy in low Arctic tundra, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17304, https://doi.org/10.5194/egusphere-egu26-17304, 2026.
Air temperature is a critical regulator of ecosystem functions, including the release of biogenic volatile organic compounds (BVOCs) that mediate biosphere-atmosphere interactions. Among these, sesquiterpenes (SQTs) stand out for their dual role as ecologically significant compounds and highly reactive atmospheric constituents. Despite the inherently complex relationship between temperature and biogenic emissions, global emission estimates rely on simplistic parameterizations, assuming a fixed exponential response across all ecosystems and environmental conditions. Here, we synthesize two decades (1997–2019) of SQT emission studies, uncovering significant variability in temperature responses and basal emission rates driven by plant functional types (PFTs) and diverse environmental co-factors. When PFT-dependent parameterizations are integrated into emission-chemistry simulations, the results reveal sensitive feedbacks on atmospheric processes, including ground-level ozone (O₃) production and secondary organic aerosol (SOA) formation. Surprisingly, we identify a statistically significant decline in SQT temperature responses over time, suggesting that evolving environmental changes are reshaping the fundamental relationship between temperature and SQT emissions. This meta-analysis highlights the temperature sensitivity of sesquiterpenes (βSQT) as a key parameter at the interface of the biosphere, abiotic and biotic environmental change, and atmospheric processes, with cascading effects on air quality and climate. Our findings emphasize the potential to consider βSQT as a "volatile stressometer" for ecosystem-atmosphere interactions, where environmental stresses regulate the emission responses, with cascading effects on atmospheric chemistry and wider implications for future climate-vegetation feedbacks.
How to cite: Bourtsoukidis, E., Guenther, A., Wang, H., Economou, T., Lazoglou, G., Christodoulou, A., Christoudias, T., Nölscher, A., Yañez-Serrano, A. M., and Peñuelas, J.: Environmental change is reshaping the temperature sensitivity of sesquiterpene emissions and their atmospheric impacts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6630, https://doi.org/10.5194/egusphere-egu26-6630, 2026.
Biogenic volatile organic compound (BVOC) emissions from European vegetation are a major precursor of tropospheric ozone and remain a key uncertainty in regional air-quality modelling. We present two high-resolution (0.1° × 0.1°) European BVOC emission datasets developed within the EU SEEDS project aimed at supporting scientific development within Copernicus Atmospheric Monitoring Service (CAMS). The datasets include BVOC species consistent with the RACM chemical mechanism and are generated by coupling the SURFEX land surface model with the MEGAN3.0 emission model.
Emissions based on two land surface model simulations were analysed: (i) an open-loop SURFEX simulation available for 2018–2022, and (ii) a data-assimilation simulation in which satellite leaf area index (LAI) observations are assimilated, available for 2018–2020. In both cases, SURFEX is configured to allow vegetation phenological responses to meteorological variability, enabling a realistic representation of phenology. Evaluation against independent datasets shows that both simulations capture temporal variability in LAI and root-zone soil moisture, with improved skill in the analysis configuration.
Given its importance for atmospheric chemistry, we focus on isoprene emissions. Interannual and seasonal variability in isoprene emissions is shown to be primarily driven by LAI variability, with specific events (e.g. summer 2019) linked to drought-induced vegetation stress simulated by SURFEX. Daily variability in isoprene emissions is evaluated against in-situ online isoprene concentration measurements at eight western European sites, revealing moderate to strong correlations across most site-year combinations. Comparisons with other bottom-up European isoprene inventories show that SURFEX-MEGAN3.0 emissions lie between the lower CAMS-GLOB-BIOv3.1 and higher MEGAN-MACC estimates, with differences in seasonality attributable largely to the underlying LAI datasets.
These results highlight the important role of vegetation phenology, particularly LAI variability, in controlling BVOC emissions on monthly to interannual timescales, and demonstrate the added value of an Earth-system approach for BVOC emission modelling in support of air-quality assessments.
References
Hamer, . D., Markelj, M., Rojas-Munoz, O., Bonan, B., Calvet, J.-C., Marécal, V., Guenther, A., Trimmel, H., Vallejo, I., Eckhardt, S., Sousa Santos, G., Sindelarova, K., Simpson, D., Schmidbauer, N., and Tarrasón, L.: Two Biogenic Volatile Organic Compound Emission Datasets over Europe Based on Land Surface Modelling and Satellite Data Assimilation, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2025-442, in review, 2025.
How to cite: Hamer, P., Markelj, M., Rojas-Munoz, O., Bonan, B., Calvet, J.-C., Marécal, V., Guenther, A., Trimmel, H., Vallejo, I., Eckhardt, S., Sousa Santos, G., Sindelarova, K., Simpson, D., Schmidbauer, N., and Tarrasón, L.: European Biogenic Volatile Organic Compound Emissions Based on Land Surface Modelling and Satellite Data Assimilation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12967, https://doi.org/10.5194/egusphere-egu26-12967, 2026.
Predicting plant responses to changing climate, particularly to heat extremes and elevated near-ground ozone, is a key obstacle in robustly quantifying future biogenic volatile organic emissions (BVOCs) and understanding the climate feedback loop. Scaling BVOC emissions from leaf to landscape level and identifying stress-specific emission fingerprints require controlled-chamber experiments with sequential stress exposure that realistically mimic natural events.
In a climate-controlled chamber, periodic stress exposures were applied to forest (Fagus sylvatica L., Quercus robur L.) and urban tree species (Castanea sativa Mill., Tilia cordata Mill.) during summer 2024 and 2025. The forest species were exposed to heat (~40°C) and nocturnal ozone stress (100-120 ppb), while urban species experienced heat stress (~40°C) and a 72h simultaneous ozone exposure (100-120 ppb). BVOC emission fluxes were measured using proton-transfer reaction time-of-flight mass spectrometry and compared across pre-stress, heat, and combined heat–ozone conditions.
Heat stress strongly increased BVOC emissions, with urban tree species showing 2–8-fold increases in isoprene and ~3-fold increases in monoterpenes, along with elevated sesquiterpenes and green leaf volatiles. Forest species showed more selective heat-induced emissions, primarily in monoterpenes and green leaf volatiles. In contrast, combined ozone–heat stress following ozone exposure suppressed most BVOC emissions by 30–60%, largely independent of species, despite differing ozone treatments. The concurrent increase of methyl salicylate, a stress-alarm compound, emissions under combined stress compared to heat alone showed a non-additive physiological response. Heat stress consistently yielded the highest OH reactivity of BVOCs across all species and decreased by 10–30% following ozone-mixed heat exposure. A cross-investigation using machine learning and positive matrix factorization identified stress- and species-specific VOC fingerprints, with a good agreement.
These multi-stress experiments provide mechanistic insight into stress-induced BVOC emissions and could improve parameterizations of BVOC emissions in Earth system and air-quality models under increasing pollution and heat events.
How to cite: Dey, B., Depp, C., Gu, Y., Sjøgren, T. D., Khare, P., Gkatzelis, G. Ι., Wu, Y., Vasireddy, S., Knohl, A., Rinnan, R., Novelli, A., Fuchs, H., Hohaus, T., and Pfannerstill, E. Y.: Ozone alters heat-driven Biogenic VOC responses: evidence from forest and urban tree species under sequential stress, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3388, https://doi.org/10.5194/egusphere-egu26-3388, 2026.
European beech (Fagus sylvatica) is widespread and dominant in many central European forests. Increasing drought stress due to climate change has caused severe damage in beech stands across the continent (Geßler et al., 2007; Leuschner, 2020). Volatile organic compounds (VOCs) are key ecological signals during drought, mediating within-plant responses and interactions with other plants and trophic levels (Baldwin, 2010). Understanding VOC responses in European beech is therefore important for future forest management under climate change. However, the volatile profiles of European beech under drought stress remain poorly studied.
In this study, we used 72 four-year-old European beech trees from seven provenances and 12 seed families (same maternal trees), assigning them to drought and control groups in a common garden located in Zurich, Switzerland. Drought-treated trees received no water for a total of 14 days, while the control group remained well watered throughout the experiment. VOCs were sampled at three time points for both groups: before drought, after 7 days of drought treatment, and after 14 days of re-watering. A “push–pull” system was used to actively collect headspace volatiles around each whole tree into Tenax tubes, and samples were analyzed using gas chromatography–mass spectrometry (GC–MS). Features were detected and aligned among samples using MZmine (Heuckeroth et al., 2024), and peak heights were analyzed with linear models and variance partitioning to identify VOC signals related to genetic background and drought stress.
We found that several monoterpenes displayed genetically specific emission patterns under well-watered conditions, reflecting underlying genetic differentiation in VOC physiology. During drought, a large proportion of the variation in VOCs was explained by drought treatment, while the variation attributed to seed family decreased substantially. In particular, monoterpenes and green leaf volatiles indicated strong activation of stress-response pathways. Notably, a subset of drought-induced VOCs remained elevated even after re-watering, suggesting a legacy effect of drought stress. Our results show that drought-related VOC signals can serve as valuable biomarkers for assessing drought stress in European beech, thereby improving our ability to monitor tree health under climate change.
How to cite: Tang, T., Guerra, T., L. Coq—Etchegaray, D., Schimd, B., R. Castro, S., Reichert, L., C. Schuman, M., and van Moorsel, S.: How does European beech smell under drought stress? Volatile responses across genetically diverse backgrounds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4991, https://doi.org/10.5194/egusphere-egu26-4991, 2026.
Urban greening strategies are increasingly implemented to mitigate urban heat island, restore biodiversity, improve urban carbon balance and improve air quality. Yet vegetation can emit biogenic volatile organic compounds (BVOCs) that influence atmospheric chemistry. BVOCs react with oxidants such as ·OH and NO₃· radicals and O₃, contributing to secondary air pollutants such as tropospheric ozone and secondary organic aerosol (SOA). While emissions from trees in forest ecosystems are well documented, urban environments feature diverse plant types, with shrubs being the most planted type of plants in greening strategies but rarely studied in terms of VOC emissions. The few studies on mediterranean shrubs mostly focused on rosemary and thyme, and were limited to terpene emissions (isoprene, monoterpenes and sesquiterpenes, (Malik et al., 2023; Duan et al., 2023; Bourtsoukidis et al., 2024; Pei et al., 2025)) while their volatilome is probably more complex as for other plant species (Gonzaga Gomez et al., 2019; Furnell et al., 2024).
This study is aimed at providing a complete characterization of BVOC emissions from six common Mediterranean shrub species in Marseille (France), and at evaluating their potential contribution to secondary air pollution. Six species were investigated, and selected based on their abundance and their potential use in vegetation initiative : Rosmarinus officinalis, Thymus vulgaris, Photinia fraseri, Euphorbia characias, Viburnum tinus and Ligustrum vulgare. Dynamic enclosure measurements were used to collect BVOCs for 3 different commercial plants. A non-target approach combining online and offline measurement techniques was used to characterise BVOC emissions. Proton Transfer Reaction Time of Flight Mass Spectrometry (PTR-ToF-MS) was used for online measurements, complemented by VOC sampling on TENAX tubes, analyzed by GC-MS, mainly for monoterpene speciation.
Emission profiles revealed high chemical diversity, ranging from 45 compounds in Ligustrum vulgare to 91 VOCs in Thymus vulgaris emissions. Oxygenated VOCs (OVOCs) dominated the emissions of all species (60–66%) including Thymus vulgaris and Rosmarinus officinalis, which have previously only been considered monoterpene emitters (Gros et al., 2022; Francolino et al., 2023). The emissions of OVOCs such as methanol, acetone, and acetic acid often exceeded those of monoterpenes. The non-target approach used here enabled the detection of unexpected compounds, such as dimethyl sulfide (DMS, C2H6S), typically associated with marine sources, suggesting specific processes that will be discussed.
Ozone Formation Potential (OFP) varied over several orders of magnitude among the 6 species: Rosmarinus officinalis (43.7 g O₃ g VOC⁻¹), Thymus vulgaris (13.1 g O₃ g VOC⁻¹), Photinia fraseri (6.8 g O₃ g VOC⁻¹), Euphorbia characias (3.5 g O₃ g VOC⁻¹), Viburnum tinus (1.7 g O₃ g VOC⁻¹), and Ligustrum vulgare (0.2 g O₃ g VOC⁻¹). The SOA formation potential of these emissions also warrants further investigation to fully assess their contribution to urban atmospheric reactivity. These results indicate that species selection in urban greening projects can strongly influence air quality outcomes. Our findings provide emission factors for Mediterranean shrubs and highlight the need to integrate BVOC data into urban vegetation planning to minimize the formation of secondary pollutant.
How to cite: Paye, M. F. N., Rocco, M., Durand, A., Monod, A., and Kammer, J.: BVOC Emissions from Mediterranean Urban Shrubs: Implications for Ozone Formation and Air Quality, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16883, https://doi.org/10.5194/egusphere-egu26-16883, 2026.
Biogenic volatile organic compounds (bVOCs) constitute a highly complex and diverse group of chemicals emitted into the atmosphere by the Earth’s biosphere. Through atmospheric oxidation, they alter the mixing ratios of trace gases such as methane, carbon monoxide, and tropospheric ozone. Moreover, oxidation products contribute to aerosol formation, which plays a crucial role in Earth’s radiative balance and air‑quality regulation.
Projected rises in global temperatures over the coming decades are expected to produce warmer and drier conditions in Alpine regions, resulting in combined heat‑ and drought‑stress for forest ecosystems. Understanding how trees respond to these co-occurring abiotic changes is essential for assessing impacts on atmospheric chemistry and secondary organic aerosol (SOA) properties.
We conducted controlled laboratory experiments spanning the peak growing season (July to October) to examine the effects of elevated temperature (heat, +4°C above average), reduced water availability (drought, 50% decrease in volumetric soil water content), and their combination on conifer seedlings grown from seeds collected in the Pfynwald Long‑Term Irrigation Experiment (established in 2003). By using offspring from Scots pine mother trees that experienced contrasting water regimes (naturally dry versus artificially irrigated), we assessed both immediate stress responses and potential maternal‑priming effects on bVOC emissions. Specifically, we investigated (i) bVOC precursors in conifer needles (secondary metabolites) and (ii) bVOC emissions in the gas phase.
To achieve this, we (i) developed an analytical method for extracting and chromatographically separating terpenes and terpenoids from conifer needles, and (ii) designed and built a novel plant chamber for bVOC gas‑phase measurements - online with a PTR‑ToF‑MS and offline with thermodesorption‑GC‑MS.
We present results illustrating terpenes and terpenoid in conifer needles and in the gas-phase from seedlings under different maternal water availability and compare baseline conditions to heat and drought stress. We hypothesize that parental environmental history influences offspring stress responses, and that incorporating these mechanisms into Earth‑system models will improve predictions of bVOC emissions and their feedbacks on atmospheric chemistry under future climate scenarios.
How to cite: Pieber, S. M., Molteni, U., Luo, N., Hunziker, S., Bose, A., Faiola, C., Kalberer, M., and Gessler, A.: Does Parental Environment Prime Offspring bVOC Responses to Heat and Drought in Scots Pine?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17831, https://doi.org/10.5194/egusphere-egu26-17831, 2026.
Arctic regions are experiencing rapid and disproportionate warming, with consequences for plant ecophysiology and the frequency and severity of insect herbivory outbreaks. Although the individual effects of warming and herbivory on Arctic vegetation and associated biosphere–atmosphere feedbacks have received increasing attention, their combined impacts remain insufficiently understood. Because climatic and biotic stressors frequently co‑occur, identifying whether their effects are additive, synergistic, or antagonistic is critical for predicting future ecosystem functioning.
We conducted a 13-week mesocosm experiment in controlled climate chambers using shrub-dominated plant communities (Salix spp.). The experiment included a 2-week acclimation, an 8-week treatment phase, and a 3-week recovery period. During the treatment phase, we applied four conditions: (1) ambient control, (2) warming (+5 °C, including a +5 °C heat wave in week 8), (3) herbivory by geometrid moth larvae (15 larvae added between weeks 5–7), and (4) combined warming and herbivory. CO₂ exchange was measured continuously throughout the experiment, while volatile organic compound (VOC) emissions via sorbent cartridges were quantified at four time points: weeks 8, 9, and 10 during treatments, and once in week 12, during the recovery period. Plant phenology was continuously monitored using greenness indices before, during, and after the 13-week experimental period.
Combined warming and herbivory strongly enhanced isoprene emissions by ~13-fold, whereas neither stressor alone produced a significant effect on VOC emissions. Isoprene emissions were highest in week 8, followed by a gradual decline during the following weeks, suggesting a transient stress-induced response. Phenological dynamics showed limited treatment sensitivity, although control plants exhibited a slower decline in greenness late in the season, suggesting that stressed plants may enter senescence earlier. CO₂ flux measurements indicated treatment-related trends in carbon exchange, though further analysis is ongoing.
Our results demonstrate that simultaneous climatic and biotic stressors can intensify VOC emissions and influence CO₂ exchange in Arctic shrubs, with potential consequences for atmospheric chemistry and carbon cycling. Incorporating multi‑stressor interactions into ecosystem models will be essential for accurately predicting vegetation–atmosphere feedbacks in a rapidly changing Arctic.
How to cite: Contreras-Serrano, M., Rinnan, R., Tang, J., and Li, T.: Combined Warming and Herbivory Stress Intensifies Isoprene Emissions and Alters CO2 Exchange in Arctic Shrubs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7499, https://doi.org/10.5194/egusphere-egu26-7499, 2026.
Insect herbivory is a major disturbance in subarctic ecosystems, yet its impact on biogenic volatile organic compound (BVOC) emissions from understory vegetation remains poorly understood. Here, we use a severe, natural geometrid moth outbreak in a mountain birch forest in northern Fennoscandia to quantify i) outbreak-associated changes in understory vegetation and ii) indirect effects of mountain birch canopy loss on understory microclimate and BVOC emissions. Across two growing seasons (moderate herbivory vs. peak outbreak), we combined enclosure BVOC measurements (n = 131) from three dominant understory plant species with near-surface spectral proxies of vegetation greenness and microclimatic data.
The geometrid outbreak caused widespread mountain birch canopy defoliation and reduced understory greenness. Moreover, mountain birch canopy loss increased incident solar radiation in the understory, raised understory canopy surface temperature, and reduced soil moisture. Despite these warmer and brighter conditions, which typically promote BVOC release, understory BVOC emissions declined in the outbreak year, indicating that loss of photosynthetic tissue constrained emission capacity. Empetrum nigrum showed the strongest reduction in total BVOC emissions (72%) despite a pronounced shift toward stress-induced blends during the outbreak year. Total emissions of Vaccinium myrtillus were reduced by 55% and showed modest compositional change including late-season increases in isoprene under warm, high-PAR conditions in the outbreak year. Graminoids were comparatively resilient, showing limited compositional shifts and only minor reductions in total BVOC emissions.
Together, these results indicate that BVOC emissions from subarctic understories are jointly controlled by direct herbivory and canopy-mediated microclimatic feedbacks, and that large-scale insect outbreaks can directly or indirectly suppress, rather than enhance, BVOC emissions when green leaf loss outweighs biochemical induction. Accounting for these coupled pathways is essential for predicting biosphere–atmosphere interactions in a warming Arctic where insect outbreaks are expected to intensify.
How to cite: Laursen, S. N., Feng, S., Smart, A., Grillini, F., Rieksta, J., Jao, Y., Davie-Martin, C. L., Rinnan, R., and Westergaard-Nielsen, A.: Coupled insect-outbreak and microclimatic forcing suppresses BVOC emissions in subarctic understory plants, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17295, https://doi.org/10.5194/egusphere-egu26-17295, 2026.
Subarctic forests act as major emitters of biogenic VOCs and important carbon sinks whose balance can be rapidly altered by biotic and abiotic stressors. We analyzed the diel cycles of major VOCs during the growing seasons of 2021, 2022, and 2023 in a subarctic mountain birch forest (Betula pubescens) near Abisko, northern Sweden. Herbivory stress caused by caterpillar outbreaks was associated with changes in VOC emissions, particularly during the complete defoliation event in 2023, highlighting the importance of incorporating VOC dynamics into assessments of ecosystem responses to disturbance and climate change.
Complementing VOC observations, we examined CO₂ fluxes using four years (2021-2024) of eddy covariance data. The 2023 outbreak transformed the forest from a near-neutral carbon balance to a strong source (annual NEE = +150.147 gC m⁻²), compared to modeled undisturbed conditions predicted by RandomForest (+0.195 gC m⁻²) and LPJ-GUESS (−102.637 gC m⁻²). In the recovery year (2024), the observed balance returned to +5.168 gC m⁻². These findings demonstrate that insect outbreaks simultaneously disrupt carbon dynamics and biogenic VOC emissions, reinforcing the need to integrate both processes into models of northern ecosystems under climate change.
How to cite: Egea Guevara, A., Holst, T., Davie-Martin, C. L., Rieksta, J., Smart, A., Rinnan, R., and Seco, R.: BVOCs and CO₂ fluxes under an herbivory outbreak in a Subarctic Birch Forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13173, https://doi.org/10.5194/egusphere-egu26-13173, 2026.
Future warming of the Arctic may increase emissions of VOCs and GHGs, such as methane (CH4), into the atmosphere. Disintegration of cryospheric caps (permafrost and glaciers) can lead to increase in geogenic carbon emissions, alongside active layer biogenic emissions, and geogenic sources represent an overlooked feedback of atmospheric forcing from permafrost melting. However, the magnitudes, diversity, and partitioning of geogenic and biogenic VOCs and associated CH4 remain unknown, and therefore, we have limited understanding of how important different VOC and CH4 sources are for atmospheric interactions of melting Arctic permafrost landscapes.
We studied VOC and CH4 emissions in Nuussuaq (70°29′57.16″ N, 54°10′35.91″ W) in west Greenland with known natural geogenic gas and oil seeps. During a 10-day period, we collected gas samples from in situ gas seeps at lakes on top of geological fault zones, springs, and permafrost thaw ponds to capture the variation in VOC and CH4 compositions and emission rates in areas with different geogenic impacts. Furthermore, we measured net fluxes of VOCs, CH4, N2O and CO2 across a geomorphological and soil gradient (alluvial fan with sand to hydromorphic palsa rich in organic matter) underlain by permafrost, to gain insight into spatial drivers of diversity and partitioning of VOC and GHG fluxes in an Arctic landscape.
Preliminary results for VOCs across the geomorphological gradient show significant contribution to terrestrial emissions from vegetation, dominated by moss and Arctic shrubs, especially from the terpenes (+)-α-longipinene and (+)-camphor. Emission rates from waterbodies and wetland were smaller compared to terrestrial emissions, but VOC diversity was high, including compounds like acetone, 2-methylbutane, 2-ethyl-1-hexanol, benzaldehyde, and benzonitrile – potentially originating from both geogenic and biogenic sources. However, terpenes dominating terrestrial emissions were also observed abundantly in the water samples. In addition to VOCs, we will also present the flux data on CH4, N2O and CO2 and VOC data for lakes and springs to corroborate whether geogenic VOC’s are emitted.
How to cite: Christiansen, J., Adnew, G. A., Schroll, M., Juncher Jørgensen, C., and Roslund, K.: Geogenic and Biogenic Volatile Organic Compounds in an Arctic Permafrost Landscape, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11845, https://doi.org/10.5194/egusphere-egu26-11845, 2026.
Biogenic volatile organic compounds (VOCs) play important roles in atmospheric chemistry, yet most studies have focused on canopy emissions. Decomposition of forest litter, a major below-canopy VOC source, can substantially influence atmospheric oxidation and aerosol formation. Scots pine (Pinus sylvestris L.), one of the most widely distributed tree species across the boreal zone, produces terpene-rich litter that may represent a significant but understudied VOC source. Here, we incubated fresh needle litter under controlled temperature and moisture levels to quantify VOC and CO2 fluxes. Monoterpenoids overwhelmingly dominated emissions (91%), with oxygenated species such as camphor and 2,5-bornanedione being most abundant. Moisture was the main control: water addition increased monoterpenoid fluxes five- to seven-fold relative to drier treatments, consistent with stimulation of microbial activity. Temperature had a weaker but compound-specific influence, strongest for sesquiterpenoids. Isoprene increased while oxygenated VOCs declined over time, indicating a transition from stored-pool release to microbial processes. Specifically, the strong correlation between monoterpenoid and CO2 fluxes points to shared microbial processes and highlights the key role of moisture in VOC release from decomposing pine litter. This relationship may also offer a potential practical basis for estimating monoterpenoid emissions from pine-dominated forest floors using CO2 flux data.
How to cite: Jiao, Y., James, S. M., Zhang, Z., Roslund, K., Lehner, I., Biermann, T., Tang, J., and Rinnan, R.: High Monoterpenoid Emissions from Scots Pine Litter Controlled by Moisture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11489, https://doi.org/10.5194/egusphere-egu26-11489, 2026.
Volatile organic compound (VOC) emissions from forests are typically attributed to tree canopies, while the forest floor remains comparatively understudied despite its complex mixture of litter, soil microbes, and understory vegetation. Here we report first results from a pilot study, in which we measured forest-floor VOC fluxes in a mountain pine–juniper (Pinus sylvestris, Juniperus communis) stand, at the Forest Atmosphere Interaction Research (FAIR) site of the University of Innsbruck in Mieming, Austria. The site is characterized by a relatively open tree canopy dominated by pines, and a forest floor that is almost completely covered by vegetation, including dominant juniper individuals. We compared mean soil emissions with ecosystem-scale VOC fluxes obtained at the same site during a period shortly after the soil measurements, to assess the relative contribution of the forest floor to whole-ecosystem VOC exchange.
Using a dynamic chamber approach coupled to online VOC detection using Proton Transfer Reaction Mass Spectrometry (PTR-MS), we quantified forest floor emissions at two locations: (i) a site dominated by pine needle litter and mosses, and (ii) a site where moss and litter co-occurred with heather (Erica herbacea), some Polygala chamaebuxus and various grasses (Sesleria ssp., Carex ssp.) understory.
Both sites emitted substantial amounts of terpenoid compounds, such as monoterpenes and sesquiterpenes, but also isoprene, as well as oxygenated compounds such as methanol, acetaldehyde and acetone. The emissions were temporally variable and differed between the two micro-sites, consistent with differences in biological composition, substrate and meteorological conditions. While the exact sources cannot be resolved from these measurements alone, plausible contributors include microbial activity within soil and the litter–moss layer, as well as root and shoot emissions from understory shrubs.
A comparison of the forest floor VOC fluxes with the total ecosystem exchange revealed that the mean soil fluxes of many VOCs were on the order of a few to about 40 % of the respective ecosystem fluxes. Strikingly, for sesquiterpenes the soil emissions at both microsites exceeded ecosystem-scale fluxes by about a factor three and seven, respectively. This discrepancy suggests substantial within-canopy loss processes (e.g., rapid oxidation or deposition) and/or differences in temporal representativeness between the datasets.
These findings expand the known role of the forest floor as an active VOC source and suggest that bottom-up budgets that focus solely on canopy emissions may underestimate ecosystem-scale fluxes, especially under conditions favorable to microbial or understory vegetation activity.
How to cite: Jud, W., Götz, L. M., Hammerle, A., Karl, T., Schmack, J. S., Spielmann, F., and Wohlfahrt, G.: Forest floor VOC emissions in a mountain pine–juniper stand: magnitudes, composition, and implications for ecosystem-scale fluxes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17215, https://doi.org/10.5194/egusphere-egu26-17215, 2026.
Soil emissions of biogenic volatile organic compounds (BVOCs) and their impacts at the ecosystem scale have been intensively studied. However, less attention has been paid to how forest management practices alter soil BVOC exchange by modifying soil physical and biogeochemical properties. In managed forests, timber harvesting operations frequently create skid trails, where repeated machine traffic leads to soil compaction and impaired drainage, potentially altering oxygen availability and microbial processes.
In this study, we investigated how soil property changes associated with skid trails influence BVOC exchange from the forest floor of the ECOSENSE forest, a temperate mixed forest. We combined field measurements of soil–atmosphere BVOC exchange at waterlogged skid trails and adjacent undisturbed forest floor with laboratory incubations of intact soil cores under controlled oxic and anoxic conditions.
Our results show that skid trail soils exhibit distinct BVOC emission patterns compared to well-drained forest soils. In particular, emissions of aromatic compounds, including toluene and the aromatic monoterpene p-cymene, increased markedly under waterlogged and oxygen-limited conditions. Emissions of several monoterpenes, such as α-pinene, camphene, limonene, and δ-3-carene were also enhanced.
Although skid trails cover only a small fraction of the forest area, our findings indicate that they can act as BVOC emission hotspots within forest ecosystems. This highlights that small-scale heterogeneity introduced by forest management can substantially influence ecosystem-level BVOC budgets and forest–atmosphere interactions.
How to cite: Lee, H., Stippich, T., Petersen, J., Meine, D., Brzozon, J., Sulzer, M., Christen, A., Kattenborn, T., Dedden, L., Werner, C., and Kreuzwieser, J.: Soil compaction by forest management creates hotspots of BVOC emissions in a temperate mixed forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3031, https://doi.org/10.5194/egusphere-egu26-3031, 2026.
Petrichor – a strong scent released from desiccated soil upon rewetting – is a mixture of volatile organic compounds (VOCs) that impact atmospheric chemistry and originates from the abiotic desorption of stored compounds and the de novo microbial production. The aridity gradient of the Negev Desert soils provides a particularly suitable system for studying petrichor emissions due to their distinctive and well-studied microbial communities (e.g., Actinobacteria and Cyanobacteria) but similar physical properties that control VOC physical evaporation, and absence of plant material as confounding sources of VOCs. While the chemical and microbial origins of petrichor are relatively well described, the controlling factors of its emission remain unclear. This study investigated the influences of desiccation dynamics on petrichor emissions and microbial succession in soils from an aridity gradient of the Negev Desert in Israel. Soil cores were subjected to three sequential rain events followed by contrasting desiccation regimes (long drought, rapid desiccation and slow desiccation) in a realistic climate simulation. Their VOC emissions and microbial metatranscriptomics were studied at five time points, including three upon rewetting and two during slow desiccation. The results showed that VOCs were produced during soil drying, with compound-specific release patterns occurring either during desiccation or upon rehydration. Despite having a common biosynthetic pathway, monoterpenoid and sesquiterpenoid emissions exhibited distinct temporal dynamics, suggesting different underlying physical control or microbial activity. The abundances and chemical diversity of petrichor decreased with increasing aridity, closely following the decline in microbial diversity. The microbial communities varied among rewetting scenarios and exhibited clear temporal succession during slow desiccation, likely regulating petrichor emissions through microbial activation. Greater community dispersion at 24 hours after rewetting indicated rapid and heterogeneous microbial reactivation, potentially contributing to increased variability and reduced predictability of early petrichor emissions. These findings highlighted the importance of desiccation rate in controlling petrichor emissions in desert ecosystems. Further field measurements and functional microbial analyses will be essential to understand how changing desiccation regimes will reshape petrichor emissions and the microbial communities in desert ecosystems.
How to cite: Nguyen, H. A., Gevogyan, H., Poodiack, B., Weber, B., Schnitzler, J.-P., Siebner, H., Gillor, O., Bonkowski, M., and Ghirardo, A.: Effects of desiccation dynamics on petrichor emissions in Negev Desert soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21092, https://doi.org/10.5194/egusphere-egu26-21092, 2026.
Biogenic Volatile Organic Compounds (BVOCs) are a group of highly reactive chemical compounds that are emitted by the terrestrial biosphere. They play a crucial role in atmospheric chemistry by contributing to the formation of tropospheric ozone, secondary organic aerosols (SOA) and cloud condensation nuclei, thereby influencing both air quality and climate processes. However, quantifying their exchange between ecosystems and the atmosphere remains challenging due to the interplay of measurement complexities, heterogeneous surface properties and vegetation variability.
For about five months from summer to autumn 2025, we conducted an intensive measurement campaign to study the BVOC fluxes at the University of Innsbruck’s Forest Atmosphere Interaction Research (FAIR) field site in Mieming, Tirol, Austria. The site is characterized by a Pinus sylvestris canopy with Juniperus communis understory and is equipped with a 30 m tall flux tower, a heated Teflon sampling line, and an air-conditioned instrument container. BVOC concentrations were measured using Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS), and turbulent fluxes were calculated via the eddy covariance technique.
Here, we investigate the temporal variability and environmental controls of BVOC fluxes with a focus on mono- and sesquiterpenes at the ecosystem scale. We further evaluate how well emission patterns align with findings from a laboratory study conducted in 2024 on saplings of the dominant species at the FAIR site, and plan to assess the performance of the MEGAN 2.1 emission model in reproducing the observed flux dynamics.
Our results provide new insights into the drivers of BVOC fluxes in an alpine forest and support the improvement of biosphere–atmosphere exchange parameterizations in emission models.
How to cite: Schmack, J., Jud, W., Karl, T., Spielmann, F. M., Wohlfahrt, G., and Hammerle, A.: Five months of BVOC flux measurements above a Pinus sylvestris forest stand in the Austrian Alps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3307, https://doi.org/10.5194/egusphere-egu26-3307, 2026.
Peatlands store the largest carbon stocks per unit area and are key regulators of climate. Carbon cycling and emissions to the atmosphere from peatlands are of critical importance and responsive climate change, with changing precipitations patterns and temperatures causing a shift in plant community composition. Yet the underlying drivers for volatile organic compound (VOC) exchange remain poorly understood. This study aims to assess the influence of different functional plant groups and environmental drivers on peatland VOC emissions.
A field study was conducted utilizing an established long-term plant removal experimental setup with 40 plots evenly distributed across four plant removal treatments (control, removal of ericoid plants, removal of graminoid plants and removal of both groups) and two microsite types (hummocks and hollows). VOC emissions were measured twice each month in the summer of 2025 using flow chambers connected to sorbent tubes analyzed by GC-MS. We measured environmental variables; PAR-light, soil and air water content/humidity and temperature concurrently with vegetation VOC measurements. We also collected species cover data on plot level.
A PCA analysis across all VOC emissions uncovered the sampling months to explain multivariate distribution with clustering of all months and especially June standing out. The emission profiles were dominated by isoprene in July (80.7%) and August (87.8%) while in June oxygenated VOCs dominated the total emission (66.8 %). Linear mixed models showed a significant effect of month, treatment, microsite and the interactive effects of month and treatment and month and microsite on isoprene emissions. The highest mean isoprene emission appeared in July; the emissions were higher from hollow microsites than hummocks and the treatments with removal of graminoid plants had lower isoprene emissions compared to both other treatments. Only difference in month had a significant effect on the oxygenated VOC emissions, with OVOC emissions in June being more than tenfold than in the other months. Difference in month also significantly affected all other VOC groups. PLS models showed emissions of all groups except sesquiterpenes to significantly increase with air temperature, while soil temperature, water table depth and soil moisture significantly influenced emissions of isoprene, sesquiterpenoids, and OVOCs. The presence of ericoid plant species correlated negatively with sesquiterpene emissions while graminoid species increased isoprene emissions.
The study supports the understanding that VOC emission abundance and composition are influenced by environmental drivers and plant species composition, while the seasonal variation, even within summer months can be of significant size. Especially OVOC emissions seem responsive to a change in soil moisture, dominating the total emissions in the driest month.
How to cite: Bloch Carlsson, M., Jiao, Y., Rinnan, R., and Robroek, B.: Effects of Vegetation and Microhabitats on Peatland VOC Emissions and Seasonal Dynamics across one Summer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17790, https://doi.org/10.5194/egusphere-egu26-17790, 2026.
Biogenic Volatile Organic Compounds (BVOC), emitted by Earth’s ecosystems, affect several chemical processes in the atmosphere that have profound climate impacts. Despite their climate relevance, global BVOC-budget estimations are still inaccurate and especially emissions originating from our oceans are poorly constrained. Marine macrophytes (i.e. macroalgae and seagrass) are a large and widespread organismal group whose BVOC emission rates are especially poorly quantified. In this study we set out to shorten this knowledge gap by quantifying ex situ with a PTR-TOF-MS the BVOC emission rates of three temperate macrophytes (Zostera marina, Fucus vesiculosus and Ulva intestinalis). To capture and increase our understanding of the variability of macrophyte BVOC-emissions, our quantifications were duplicated in two marine regions that vastly differ from each other, the eastern Atlantic (Ireland) and northern Baltic Sea (Finland). The three macrophytes emitted a large variety of BVOCs as 166 compounds were in total identified. Although many BVOCS were emitted by all macrophytes, significant differences were found in the total emission profiles, both between and within-species. Interestingly, the seagrass Zostera exhibited significantly higher overall BVOC emission rates per unit weight than the two macroalgae but also revealed clearly differing within-species emission profiles between the two regions. Of individual compounds, dimethyl sulfide (DMS) was emitted at the highest rates, but many other compounds (e.g., sesquiterpenes, C10H21O+) also showed notable emission rates. Although the most emitted BVOCs are commonly investigated compounds (e.g., DMS and terpenoids), our results show that the BVOC emissions are spread out over a large number of different compounds, suggesting that future studies would benefit from targeting a wider range of BVOCs than currently. Our results highlight macrophytes as highly variable sources of BVOCs, whose better inclusion into marine BVOC budgets should be strived for. However, more reliable data is needed, and future research should also focus on investigating the dynamics driving macrophyte BVOC emissions, their variability and eventual fate in the environment.
How to cite: Gräfnings, M., Luo, Y., Zhao, J., Fossum, K., Graeffe, F., Lei, L., Ovadnevaite, J., Ehn, M., and Gustafsson, C.: Quantifying BVOC emission rates and variability of three temperate marine macrophytes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6635, https://doi.org/10.5194/egusphere-egu26-6635, 2026.
Volatile organic compounds (VOCs) play a key role in atmospheric chemistry by contributing to tropospheric ozone and secondary organic aerosol formation and by modulating the atmospheric lifetime of methane. Although the majority of atmospheric VOCs originate from biogenic emissions, dry deposition to ecosystems is increasingly recognized as an important sink influencing global budgets. While deposition processes have been quantified for a limited number of highly water-soluble VOCs, they remain poorly constrained for many other compounds.
Using a PTR-ToF-MS instrument, we measured VOC concentrations and fluxes above and below the canopy at the mixed temperate forest ICOS station of Vielsalm (Belgium) over three growing seasons (spring to autumn) between 2022 and 2024 (Dumont et al., 2026). Minimal deposition velocities were derived from negative net fluxes, and a two-layer (canopy and soil) big-leaf resistive model was applied for conceptual interpretation.
Above the canopy, significant deposition was detected for 47 VOC groups, identified by their mass-to-charge ratio (m/z) and spanning a wide range of physicochemical properties. Median deposition velocities ranged from 0.4 cm s⁻¹ for formic acid to 1.5 cm s⁻¹ for m/z 137.060 (C₈H₈O₂H⁺, aromatic OVOCs). Aerodynamic and quasi-laminar boundary layer resistances were negligible compared to the total resistance, while below-canopy uptake contributed only about 10% of the above-canopy deposition. This indicates that canopy processes represent the dominant regulation to VOC uptake.
The widely used Wesely (1989) deposition scheme reproduced the observed deposition velocities only for a subset of highly water-soluble compounds, as indicated by their high Henry’s law constants (e.g. formaldehyde, formic acid, acetic acid, hydroxymethyl hydroperoxide). For most of these low-molecular-weight OVOCs, deposition increased with relative humidity and peaked in autumn, when humid conditions were most frequent.
For many other VOCs, however, the Wesely model underestimated deposition by up to three orders of magnitude. Additional physicochemical properties were examined to account for the high deposition velocities of hydrophobic VOCs. Under dry conditions, deposition velocities were positively correlated with the octanol–air partition coefficient, used here as a proxy for solubility in lipid phases. This suggests uptake pathways not captured by current deposition models, such as dissolution into the waxy leaf cuticle or lipid membranes. Under wet conditions, this relationship weakened, and the Henry’s law constant emerged as the strongest predictor of deposition. These findings were supported by an independent VOC flux dataset acquired over a winter wheat field in the Paris region (Loubet et al., 2022), where a similar dependence on the octanol–air partition coefficient was observed.
Overall, our results indicate that both aqueous and lipid reservoirs within vegetation can contribute to VOC dry deposition and should be treated as complementary uptake pathways. Building on these findings, this ongoing work will aim to extend existing deposition models to predict the uptake of both hydrophilic and hydrophobic organic compounds by ecosystems.
How to cite: Dumont, C., Verreyken, B., Schoon, N., Loubet, B., Amelynck, C., and Heinesch, B.: Beyond water solubility: physicochemical controls on VOC dry deposition in a mixed temperate forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17720, https://doi.org/10.5194/egusphere-egu26-17720, 2026.
Total ozone (O3) reactivity measurements are rare, even though they are an important tool to assess the extent of the identification and quantification of volatile organic compounds (VOCs) reacting with ozone. This includes a large fraction of VOCs from biogenic sources such as trees and other vegetation. So far, only a few studies have investigated total O3 reactivity from biogenic emissions under controlled conditions (Matsumoto, 2014; Sommariva et al., 2020) or in situ (Thomas et al., 2023). In the present study, we compile previously unreported measurements of total O3 reactivity made during four distinct campaigns conducted between 2010 and 2020.
Two total ozone (O3) reactivity monitors (TORMs; Helmig et al., 2022) were used. The first one at the University of Michigan Biological Station (UMBS) during the 2010 CABINEX campaign to study emissions from red oak, white pine, red maple, and bigtooth aspen, and at the Alabama Aquatic Biodiversity Center (AABC) during the 2013 Southeast Oxidant Aerosol Study (SOAS) campaign to study emissions from sweetgum, white oak and loblolly pine. The second TORM was used at the University of Alaska Toolik lake field station (TFS) in 2019 to study emissions from tundra surface vegetation and at a boreal fen in Finnish Lapland (Lompolojänkkä) in 2020 to study emissions from the fen’s surface. Simultaneously, the chemical composition of the emissions was analysed by chromatographic methods.
TORM directly measures the amount of ozone lost in its reactor when O3 is mixed with sampled air. However, the derivation of total O3 reactivity from the measured O3 loss is not straightforward, particularly in the presence of fast-reacting compounds, such as β-caryophyllene. This invalidates the assumptions made in the equation used to calculate total O3 reactivity. For a more straightforward approach, we compared the measured O3 loss in the reactor against the expected O3 loss, which is modelled from identified VOCs and their reaction rate coefficients with O3. In most cases, the measured O3 loss was found to be higher than the expected one. Even after considering the uncertainties related to the quantification of VOCs, uncertainties of reaction rate coefficients, and uncertainties related to the direct measurement of O3 in TORM, unexplained O3 losses were consistently found during daytime, indicating unidentified biogenic VOC emissions.
References
Helmig, D., A. Guenther, J. Hueber, R. W. Daly, W. Wang, J.-H. Park, A. Liikanen, and A. P. Praplan. (2022). Ozone reactivity measurement of biogenic volatile organic compound emissions, Atmos. Meas. Tech., 15, 5439.
Matsumoto, J. (2014). Measuring Biogenic Volatile Organic Compounds (BVOCs) from Vegetation in Terms of Ozone Reactivity, Aerosol Air Qual. Res., 14, 197.
Sommariva, R., L. J. Kramer, L. R. Crilley, M. S. Alam and W. J. Bloss. (2020). An instrument for in situ measurement of total ozone reactivity, Atmos. Meas. Tech., 13, 1655.
Thomas, S. J., T. Tykkä, H. Hellén, F. Bianchi and A. P. Praplan. (2023). Undetected biogenic volatile organic compounds from Norway spruce drive total ozone reactivity measurements, Atmos. Chem. Phys., 23, 14627.
How to cite: Praplan, A. P., Thomas, S. J., Daly, R. W., Park, J.-H., Wang, W., Liikanen, A., Angot, H., Hueber, J., Bianchi, F., Guenther, A., and Helmig, D.: Total ozone reactivity measurements indicate unidentified biogenic emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16671, https://doi.org/10.5194/egusphere-egu26-16671, 2026.
Isoprene accounts for half of the global BVOC emissions from terrestrial ecosystems. Consequently, refining its representation in numerical models is essential for accurately assessing its effects on Ozone and Secondary Organic Aerosols and, more generally, on the role of vegetation in modulating atmospheric physico-chemical processes. Here, we present an analysis and preliminary results of an improved parameterization of Isoprene emissions factor sensitivity to water availability and surface air temperature within the MEGAN model coupled with the Community Land Model (CLM-4.5). Overall, by comparing our results with three (quasi-)observational datasets, the new parameterization yielded more accurate estimates of global annual Isoprene emissions, despite still exhibiting less pronounced seasonal variability. Notably, more realistic values are obtained in the Arctic during boreal summer, as well as stronger emission reductions occur during periods of droughts in the tropics and in subtropical latitudes. Although uncertainties still persist in specific geographic regions, we investigate the specific model and environmental factors contributing to these discrepancies.
How to cite: Mastropierro, M., Cardeli, B., and Peano, D.: Effects of temperature and soil water parameterization improvements in MEGAN-CLM Isoprene emissions: a model-observations assessment., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13216, https://doi.org/10.5194/egusphere-egu26-13216, 2026.
Biogenic volatile organic compounds (BVOCs) are dominant precursors of tropospheric ozone and secondary organic aerosols, making their accurate representation critical for air quality modeling. Current BVOC emission estimates rely heavily on satellite-derived Plant Functional Type (PFT) maps, which often exhibit substantial discrepancies and fail to capture detailed land-use characteristics in heterogeneous agricultural and urban landscapes. To address these limitations, this study developed a new regional PFT dataset by integrating field-surveyed forest information from the Korea Forest Service’s Forest Geographic Information System (FGIS). We applied a machine learning approach to extrapolate the high-resolution, observation-based PFT characteristics of the Korean Peninsula to the broader East Asian region, utilizing meteorological variables and satellite land-cover products as predictors. The generated PFT dataset was implemented into the biogenic emission module of the Community Multiscale Air Quality (CMAQ) model to evaluate its impact on air quality simulations. We validated the model performance by comparing simulated BVOC mixing ratios with airborne observations from the ASIA-AQ campaign. The results demonstrate that the proposed PFT dataset yields distinct spatial emission patterns compared to conventional satellite-based maps. Notably, the simulation showed improved consistency with observations, particularly over complex terrain and mixed land-use areas. These findings suggest that regionally optimized PFT inputs, grounded in field observations and machine learning, significantly reduce uncertainties in BVOC emission inventories and subsequent chemical transport modeling over East Asia.
Acknowledgment: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government (MSIT) (No. RS-2025-16070879).
How to cite: jung, J., Kim, M. J., Choi, D.-R., Hong, S.-C., Lee, J.-B., and Lee, Y.: Improving East Asian BVOC Emission Estimates via Machine Learning-Based Plant Functional Types Mapping , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6225, https://doi.org/10.5194/egusphere-egu26-6225, 2026.
Volatile organic compounds (VOC) are exchanged between the Earth’s surface and the atmosphere. Their role in biosphere-atmosphere-climate interactions have been extensively studied in various and often inherently interdisciplinary research topics. Crucial to the understanding of these processes is the fast quantification of VOCs both primarily emitted as well as products and intermediates. Monoterpenes are an important class of VOCs contributing 15% to the global VOC emissions from terrestrial ecosystems. The most dominant isomeres of monoterpenes in the atmosphere are α-pinene, β-pinene, limonene, myrcene, camphene, and sabinene that are emitted in variable fractions depending on sources and conditions. In the atmosphere, monoterpenes may undergo rapid conversion via reactions with hydroxyl- and nitrate-radicals and ozone, forming oxidation products that eventually condense to secondary organic aerosol at high yields. Reaction rates of the different isomers with OH, O3 and NO3 spread up to orders of magnitude (0.8, 4.4 and 2.3 orders, respectively). Therefore it is of uttermost importance to quantify individual isomers to understand the reactivity of the mix of monoterpenes in an air mass.
Proton-transfer-reaction mass-spectrometry (PTR-MS) is a well characterized analytical method for the real-time quantification of VOCs including monoterpenes. The drawback of PTR-MS is the detection of VOCs on a chemical composition level, hence, only the sum of monoterpenes can be measured. To solve this problem, we herein introduce an optimized fast gas-chromatographic pre-separation solution (fast-GC) that is seamlessly integrated to an ultrasensitive FUSION PTR-TOF 10 (IONICON Analytik, Austria).
The improved fast-GC design allows for fast and precise heating rates leading to highest stability and repeatability of GC-runs. A temperature ramp can be completed as quick as 90 s providing resolutions sufficient for a good separation of several monoterpene isomeres. A fast-GC run can be triggered approximately every 5-10 min; the time in between runs is used to measure the ambient sample without GC separation in real-time PTR-MS mode. With the high sensitivity (> 40 000 cps/ppbV) and lowermost limit of detection (< 1 pptV in 1 s) of FUSION PTR-TOF 10, no preconcentration prior to injection of the sample into the fast-GC is required.
In this presentation we show a thorough characterization of this fast-GC FUSION PTR-TOF 10. To demonstrate the capabilities of the system in a real-world application we sampled ambient air in Innsbruck, Austria, with fast-GC runs triggered every 10 minutes continuously over the course of several weeks. Despite the low ambient concentrations of the sum of monoterpenes in sub-ppbV levels, the presented method was able to separate and quantify 7 monoterpenes.
How to cite: Graus, M., Winkler, K., Leiminger, M., Reinecke, T., and Müller, M.: Speciation of monoterpenes at atmospheric relevant concentrations without sample preconcentration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18517, https://doi.org/10.5194/egusphere-egu26-18517, 2026.
Measuring the molecular composition of small aerosol particles that have not yet grown to sizes of several 10 nm is difficult, predominately because of the little mass constituted by the particles. At the same time, composition measurements of the early particles would directly reveal the condensable species. Additionally, the chemical composition of these early particles controls the fate of the aerosol particles as it controls their robustness against evaporation.
The vaporization inlet for aerosols (VIA), coupled to an Eisele-type chemical ionisation (NO3-) inlet and a time-of-flight mass spectrometer, has been successfully demonstrated previously (Häkkinen et al 2023, Zhao et al 2023, Zhao et al 2023). Particles from a sample gas are first size selected by a differential mobility analyzer. Trace gases present in the gas phase are stripped by an active charcoal denuder. The particles are then evaporated in a sulfinert-coated stainless steel tube (OD ¼”) at temperatures up to 300 °C. The evaporated molecules are then delivered to a chemical ionization mass spectrometer. The concentration of particles entering the setup are monitored by a scanning mobility particle sizer.
Amending the experimental setup of the previous studies by a DMA for size selection before analysis, in this study we investigate how the aerosol composition differs between different particle sizes. Here, particles are first size-selected in a DMA, then vaporized in VIA. The resulting gases are ionized in a MION atmospheric pressure interface chemical ionization inlet using both positively and negatively charged reagent ions and detected in a polarity-switching high-resolution Orbitrap mass spectrometer. We demonstrate the general feasibility of the experimental approach in laboratory measurements using ammonium sulfate and a-pinene derived particles.
In ambient measurements, we show the ability to reach mass closure between the detected concentration of vaporized trace gases even at low particle sizes and low atmospheric particle concentration. We further present first results from a deployment of the novel approach to Mace Head, Ireland, where marine VOC emissions and the composition of 10-20 nm particles were targeted. Coordinated measurements of the gas and particle phase are used to constrain what species contribute to particle formation under the local conditions. The work presents a step towards closing the measurement gap of nano-particle composition and contributes to a more complete understanding of aerosol formation from more complex gas mixtures.
How to cite: Finkenzeller, H., Yli-Kujala, A., Hirvensalo, E., Zhao, J., Attoui, M., Cai, R., Koirala, M., Bengs, A., Juuti, P., Shcherbinin, A., Ehn, M., and Kangasluoma, J.: Assessing the size-resolved chemical composition of 10-50 nm particles with an online DMA-VIA-MION-Orbitrap setup, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11434, https://doi.org/10.5194/egusphere-egu26-11434, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 2
EGU26-13501 | ECS | Posters virtual | VPS5
Vegetation Dynamics and Atmospheric Glyoxal in Houston, Texas (2018-2022)Tue, 05 May, 15:18–15:21 (CEST) vPoster spot 2
Twenty years of MODIS satellite data (2002-2022), TROPOMI glyoxal observations (2018-2022), and ground-based isoprene measurements were used to examine vegetation greenness (NDVI) and atmospheric glyoxal over Houston, Texas. Biogenically produced glyoxal grew by 51% between 2018 and 2022, despite a 2% per decade decrease in summer vegetation greenness and continued urbanization. Ambient mixing ratios of isoprene, the main biogenic glyoxal precursor, paradoxically dropped by 14% within the same time frame. Temperature (+0.68°C/year), ozone (+28%), and photochemical oxidants all significantly increased over this time, according to analysis of concurrent environmental data. The results indicate that higher temperature-driven isoprene emissions (+35%) and accelerated photochemical oxidation (+10%) overcame the declining vegetation signal, resulting in net increases in atmospheric glyoxal. This suggests that Houston's remaining flora is experiencing temperature-driven changes in biogenic volatile organic compound (VOC) emissions per unit area, even while its greenness has reduced.
Keywords: MODIS NDVI; TROPOMI glyoxal; Isoprene emissions; Photochemical oxidation
How to cite: Bibi, S. and Rappenglück, B.: Vegetation Dynamics and Atmospheric Glyoxal in Houston, Texas (2018-2022), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13501, https://doi.org/10.5194/egusphere-egu26-13501, 2026.
