Oxygenated volatile organic compounds (oVOCs) emitted from non-vehicular sources, such as volatile chemical products (VCPs) and cooking, are important contributors to the total anthropogenic VOCs observed in urban regions. Models typically underrepresent oVOC emissions compared to observations and the chemical reactions that describe oVOC oxidation are often missing or misrepresented in chemical mechanisms. Here, we present multi-year efforts to update atmospheric models to better reflect the emissions and chemistry of oVOC sources. We leverage measurements from multiple ground campaigns to update emissions inventories, then use models with updated oVOC chemistry to understand how these emissions react in the atmosphere. We compare these observations to laboratory simulations of urban air conducted in the SAPHIR chamber during the Household Chemicals Amplifying Urban Aerosol Pollution (CHANEL) experiment. We demonstrate how we are using these models to better understand the detailed chemical measurements conducted in urban areas during the 2023 Atmospheric Emissions and Reactions from Megacities to Marine Areas (AEROMMA) aircraft campaign. We will discuss what implications these updates may have on model simulations of ozone production in megacities like Los Angeles, CA.

How to cite: Roska, M. and Coggon, M. and the AEROMMA and SAPHIR Team: Evaluating the emissions and chemistry of understudied VOC sources using observations from field and laboratory studies., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12518, https://doi.org/10.5194/egusphere-egu25-12518, 2025.

Urban pollution poses one of the largest threats to human health worldwide. A significant portion of this pollution is secondary, formed through atmospheric chemical reactions of emitted trace gases, with secondary organic aerosol (SOA) and ozone (O₃) being major contributors to health impacts in urban areas. While decades of air quality regulations have significantly reduced motor vehicle emissions of organic compounds that are precursors to secondary pollution, recent focus has shifted to understudied urban sources such as volatile chemical products (VCPs) and cooking emissions. These sources are complicated and challenging to replicate in chamber experiments, which typically focus on single-compound scenarios, thus limiting their comparability to real-world urban environments.

In this study, we utilized emission inventories and developed an approach to reduce the number of compounds that represent each urban source, including VCPs, gasoline, diesel, and cooking, by generating chemical fingerprints representing 80% of the overall reactivity and SOA formation potential of each urban source. These fingerprint solutions were then injected into the atmospheric simulation chamber SAPHIR to explore their potential for SOA and O₃ formation. We conducted experiments simulating each source at various NOx exposures, as well as mixed systems to simulate the urban atmosphere of US and European cities. Finally, we contextualize our findings by comparing them with data from the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) mission, offering insights into the dynamics of urban air pollution.

How to cite: Wu, Y. and the SAPHIR-CHANEL Campaign team: An Urban Emission Inventory Approach for Source Specific Atmospheric Chamber Studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3522, https://doi.org/10.5194/egusphere-egu25-3522, 2025.

Particulate nitrate is a major aerosol component worldwide that acts as a reservoir of urban nitrogen oxides (NO_x=NO+NO₂). Chemical reactions of NO_x with volatile organic compounds (VOCs) will form organic nitrates that undergo gas-particle partitioning and therefore may influence the lifetime and transport of nitrogen compounds, impacting their deposition on ecosystems.

In this study, we use data collected in chamber experiments and in ambient air to investigate how emission profiles and ambient conditions affect the gas-particle partitioning and the yield of organic nitrate. Chamber studies during the SAPHIR-CHANEL campaign show that monoterpenes, higher NO_x, and reactions with the nitrate radical in the absence of light favor the formation of organic nitrate in urban NO_x-VOC mixtures. Similar results are found at a continuous monitoring site in rural central Netherlands where the type of organic nitrate during pollution episodes depends on the airmass source and the corresponding VOC and NO_x profiles. By combining results from chamber and ambient measurements, we provide new insights into atmospheric organic nitrate chemistry.

How to cite: Nursanto, F. R., He, Q., van de Wouw, S., Zanders, A., Kroese, W. S. J., Meinen, R., Wegener, R., Adam, M. G., Winter, B., Dubus, R., Kesper, L., Rohrer, F., Holzinger, R., Hohaus, T., Gkatzelis, G. I., Krol, M. C., and Fry, J. L. and the SAPHIR-CHANEL 2024: Gas-particle partitioning and yield of organic nitrate under different VOC, NOx, and oxidation conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13407, https://doi.org/10.5194/egusphere-egu25-13407, 2025.

Managing ozone remains one of the most pressing and significant environmental challenges across megacities. Numerous studies suggest that biogenic emissions of volatile organic compounds (VOCs) play a key role in ozone formation in urban areas, yet direct evidence remains limited due to the complexity of the sources, sinks, and chemistry of biogenic VOCs. In the summer of 2021, we conducted VOC flux measurements in Beijing, a megacity in China, using the eddy covariance technique. We analyzed VOC flux data using positive matrix factorization allowing to identify prominent urban VOCs emission sources. Our findings highlight the decreasing importance of vehicle-related emissions for VOCs, while the demand for eliminating emissions from volatile chemical products has been increasing. Meanwhile, we discovered that more than half of the OH reactivity of the VOC flux originates from urban vegetation, underscoring the often-overlooked role of urban forests in air pollution. Surprisingly, the strong influence of biogenic emissions in Beijing largely governs the temperature dependence of ozone concentrations, aligning with the OH reactivity from VOC flux. This leads to ozone pollution episodes predominantly occurring on high-temperature days, when biogenic emissions, particularly isoprene, are substantially enhanced. Our study calls for a greater attention from air quality managers to the regulation of emissions from urban vegetation.

How to cite: He, X., Yuan, B., Huangfu, Y., Wang, S., Zhang, X., and Karl, T.: Insight from VOC flux measurements on managing air quality in cities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9422, https://doi.org/10.5194/egusphere-egu25-9422, 2025.

Volatile Organic Compounds (VOCs) play a key role in the formation of tropospheric ozone and secondary aerosols, influencing air quality, climate, and human health. Originating from both biogenic and anthropogenic sources, their volatile nature enables long-range transport, with oxidation products impacting distant regions. The island of Cyprus, located at the intersection of Europe, Asia, and Africa, experiences complex air mass dynamics that transport diverse VOC emissions and their oxidation products, making it a key site for studying regional air quality. However, VOC observations in the Eastern Mediterranean and Middle East region (EMME) are often constrained by the short duration of measurement campaigns and a narrow focus on specific species, resulting in a significant data gap. In this study, we employed a Proton Transfer Reaction–Time-of-Flight Mass Spectrometer (PTR-ToF-MS 4000; Ionicon Analytik, Austria) to perform continuous, high-resolution measurements of VOCs from April 2022 to June 2024 at the Cyprus Atmospheric Observatory (CAO-AMX; 35.038692° N, 33.057850° E; 532 m above mean sea level). This site represents regional background concentrations while providing valuable insights into local emission sources, including significant contributions of biogenic emissions originating from the Troodos mountain forest. We analyzed over 70 VOC species, classifying them into chemical groups such as aromatics, alcohols, aldehydes, ketones, and oxygenated VOCs. By examining their distinct seasonal and diurnal variations along with the origins of the sampled air masses, we derive valuable information about their regional and local emission dynamics and their respective impact on atmospheric chemistry. Additionally, we compared the measured VOC mixing ratios with simulations from a coupled atmospheric chemistry model (WRF-Chem) to comprehensively evaluate the model’s performance and its ability to reproduce the observed VOC variability. We find that while regional biogenic sources are reasonably well captured by the simulations, significant discrepancies for oxygenated VOCs suggest the presence of uncharacterized VOC sources in the Middle East. This work offers a unique, long-term perspective on the role of VOCs in shaping air quality in the EMME region, supporting efforts to mitigate air pollution and address climate change impacts. 

How to cite: Garg, A., Desservettaz, M., Christodoulou, A., Christoudias, T., Kanawade, V. P., Jokinen, T., Sciare, J., and Bourtsoukidis, E.: Long-term Observations of Volatile Organic Compounds at a Regional Background Site in the Eastern Mediterranean Affected by Middle Eastern Air Masses , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2702, https://doi.org/10.5194/egusphere-egu25-2702, 2025.

New particle formation (NPF) from the interactions between biogenic and anthropogenic precursors is responsible for a large portion of the sub-micron particle loadings observed in the atmosphere. Previous observations of aerosol chemical composition in these environments have found that organosulfates form in the particle phase. However, it is not clear how organosulfates form and how they contribute to the formation and growth of new particles.  We present the results of laboratory studies of NPF in a mixed organic/inorganic system including α-pinene, isoprene, sulfur dioxide and ozone in a fast flow reactor. Highly-oxidized organic compounds, organosulfates and sulfuric acid clusters were measured online with nitrate high-resolution time-of-flight (HRToF) CIMS at the end of the flow tube. Additionally, newly formed particles were collected on filters for offline analysis of their chemical composition with an ultra- performance liquid chromatography-electrospray ionization Orbitrap mass spectrometer (UPLC/(-)ESI-Orbitrap MS). There was a significant amount of oxygenated organosulfates in the particle phase, which is consistent with our previous studies. We also detected significant amounts of gas-phase organosulfates in the experimental system and found that their contribution to nucleation rates depends on the molecular size, precursor compound, and O:C ratio within the oxygenated organosulfate compound. We present detailed formation mechanisms of oxygenated organosulfates determined through MS/MS fragmentation analysis and quantum chemical modelling. Currently, parameterizations of atmospheric NPF sum the contributions of each individual chemical precursor as a separate process. Our observations demonstrate that chemical interactions of precursors in the gas and particle phase must be considered in NPF parameterizations to predict particle formation and growth in biogenic environments with transported sulfur plumes, or urban environments with abundant monoterpenes and isoprene.

How to cite: Tiszenkel, L., Vasudevan Geetha, V., Elm, J., Bryan, D., and Lee, S.: The Role of Oxygenated Organosulfates in Mixed Biogenic and Anthropogenic New ParticleFormation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12883, https://doi.org/10.5194/egusphere-egu25-12883, 2025.

Oxygenated organic molecules (OOMs), the oxidation products of organic precursors with low volatility and a high oxygen atom number, are an important driver of new particle formation (NPF) and secondary organic aerosols (SOA) formation. The sources and formation processes of OOMs are highly complicated, especially in populous regions (e.g., China) with diverse emissions of anthropogenic and biogenic precursors. However, current models fail to capture OOM formation from different precursors due to the absence of important reaction pathways (e.g., autoxidation, dimerization) and the oversimplified treatment of the oxidation of semi-volatile and intermediate-volatility precursors (I/SVOCs). In this work, we develop a Precursor-resolved Integrated two-dimensional Volatility Basis Set (I2D-VBS) model framework, which simulates the multi-generational ageing of organic emissions in the full volatility range on a precursor level and explicitly tracks irregular radical reactions, including autoxidation, dimerization, and RO isomerization followed by accelerated autoxidation. The parameterizations within the Precursor-resolved I2D-VBS are optimized by simulating chamber and flow-tube experiments measuring OOMs and SOA formed from individual precursors. We then incorporate the Precursor-resolved I2D-VBS in the CMAQ chemical transport model and simulate OOM formation in China. The CMAQ/I2D-VBS model successfully reproduced OOM concentrations at various sites across China, achieving accuracy within ±40% for total OOM concentrations and within a factor of 2 for volatility-binned OOM concentrations. The model results reveal that over 60% of total OOM concentrations are from I/SVOC in China; nevertheless, for extremely low-volatility OOMs (logC*<=-5) that are important for initial particle growth, ~60% of them are from anthropogenic VOCs in the North China Plain and ~80% of them are from biogenic VOCs in Southeast China. Multi-generational OH oxidation is the reaction pathway contributing most to OOM formation (>70%), followed by autoxidation (~20%). Overall, OOMs contribute around half of SOA concentrations in China, highlighting the critically important role of OOMs in SOA formation.

How to cite: Zhao, B., Yin, D., Wang, S., He, Y., and Donahue, N.: Sources of Oxygenated Organic Molecules and Their Impacts on Organic Aerosol in China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15281, https://doi.org/10.5194/egusphere-egu25-15281, 2025.

Volatile chemical products (VCPs) are increasingly recognized as significant sources of volatile organic compounds (VOCs) in urban atmospheres, potentially serving as key precursors for secondary organic aerosol (SOA) formation. This study investigates the formation and physicochemical transformations of VCP-derived SOA, produced through ozonolysis of VOCs evaporated from a representative room deodorant air freshener, focusing on the effects of aerosol evaporation on its molecular composition, light absorption properties, and reactive oxygen species (ROS) generation. Following aerosol evaporation, solutes become concentrated, accelerating reactions within the aerosol matrix that lead to a 42% reduction in peroxide content and noticeable browning of the SOA. This process occurs most effectively at moderate relative humidity (∼40%), reaching a maximum solute concentration before aerosol solidification. Molecular characterization reveals that evaporating VCP-derived SOA produces highly conjugated nitrogen-containing products from interactions between existing or transformed carbonyl compounds and reduced nitrogen species, likely acting as chromophores responsible for the observed brownish coloration. Additionally, the reactivity of VCP-derived SOA was elucidated through heterogeneous oxidation of sulfur dioxide (SO₂), which revealed enhanced photosensitized sulfate production upon drying. Direct measurements of ROS, including singlet oxygen (¹O₂), superoxide (O₂^•–), and hydroxyl radicals (^•OH), showed higher abundances in dried versus undried SOA samples under light exposure. Our findings underscore that drying significantly alters the physicochemical properties of VCP-derived SOA, impacting their roles in atmospheric chemistry and radiative balance.

How to cite: Zhou, L., Liang, Z., Qin, Y., and Chan, C. K.: Evaporation-Induced Transformations in Volatile Chemical Product-Derived Secondary Organic Aerosols: Browning Effects and Alterations in Oxidative Reactivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18690, https://doi.org/10.5194/egusphere-egu25-18690, 2025.

Green leaf volatiles (GLVs) are biogenic C₅ to C₆ unsaturated oxygenated organic compounds that are emitted when vegetation is exposed to herbivores, pathogens, or harsh weather conditions. Increased GLV emissions when vegetation is subjected to biotic and abiotic stresses can lead to GLVs contributing substantially to the local secondary organic aerosol (SOA). GLVs can dissolve into atmospheric aqueous phases (e.g., aqueous aerosols, cloud and fog droplets), where they can be oxidized by aqueous oxidants. Aqueous SOA (aqSOA) mass yields as high as 88 % from aqueous reactions have been reported in previous studies, but these previous studies were mostly conducted under dilute aqueous conditions mimicking aqueous cloud/fog droplets. Little is currently known about the aqueous oxidation of GLVs under more concentrated aqueous aerosol-like conditions.  Here, we investigated the nitrate-mediated photooxidation of four GLVs, cis-3-hexen-1-ol, trans-2-hexen-1-ol, trans-2-penten-1-ol, and 2-methyl-3-buten-2-ol, focusing on the effects of pH, ionic strength, and sulfate on the reaction kinetics and aqSOA mass yields under cloud/fog-like vs. aqueous aerosol-like conditions. Our results showed that the aqueous reaction medium conditions governed the effects that pH, ionic strength, and sulfate had on the reaction kinetics and aqSOA mass yields. Higher reaction rates were observed at lower pH under dilute cloud/fog-like conditions, which could be attributed to the pH-dependent formation of reactive species from nitrate photolysis. Ionic strength and sulfate had insignificant effects on the reaction rates. In contrast, under concentrated aqueous aerosol-like conditions, higher reaction rates were observed at higher pH, and at higher ionic strength and sulfate concentration. Many of these differences could be attributed to sulfur-containing radicals produced from sulfate photolysis participating in the reactions of GLVs under aqueous aerosol-like conditions, but not in cloud/fog-like conditions. Nevertheless, similar aqSOA mass yield trends were observed for cloud/fog-like and aqueous aerosol-like conditions. Higher aqSOA mass yields were measured, likely due to increased production of oligomers from RO₂· and RO· combination reactions as a result of the higher concentrations of GLVs reacted. Higher aqSOA mass yields were measured at lower pH, likely a result of increased production of low volatility products from acid-catalyzed reactions. Lower aqSOA mass yields were measured at higher ionic strength and sulfate concentration, likely due to the increased importance of fragmentation pathways in the reactions of GLVs with sulfur-containing radicals formed from sulfate photolysis. These results provide new insights that can be used in modeling studies of the atmospheric fates of GLVs and their contributions to the SOA budget.

How to cite: Nah, T., Lyu, Y., Joo, T., Ma, R., Cebello, M. K. E., Zhou, T., Yeung, S., Wong, C. K., Gu, Y., and Qin, Y.: pH, ionic strength and sulfate influence the aqueous nitrate-mediated photooxidation of green leaf volatiles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2486, https://doi.org/10.5194/egusphere-egu25-2486, 2025.

The chemical diversity of volatile organic compound (VOC) emissions from terrestrial vegetation is relatively well understood, while research on VOC emissions from freshwater and marine systems has largely focused on dimethyl sulfide (DMS) and isoprene. Through VOC concentration measurements in water samples, and VOC flux measurements using floating chambers and the direct eddy covariance (EC) technique we aim to evaluate aquatic ecosystems as sources of VOCs. Here, we present selected case studies that demonstrate the need to consider other VOCs beyond DMS and isoprene when assessing aquatic sources of atmospheric VOCs.

A survey of depth-specific VOC concentrations in water from four Alpine lakes in France showed that VOC concentrations were highest either at the deep chlorophyll maximum or at the surface. The VOC composition profiles differed between depths and lakes. In another study, we assessed net emissions of VOCs from three ponds in a rewetted peatland forest in Denmark. Again, the three ponds showed differences in the quantity and diversity of their emission profiles. Over 100 chemical species were detected, including acetone, acetaldehyde, isoprene, other terpenoids, and hydrocarbons. The most eutrophic and acidic pond had highest emission rates but lower VOC diversity compared to the alkaline ponds.

The VOC emission rates and compositions also vary over time, depending on the balance between VOC production, consumption, and emission rates, driven by both biotic and abiotic factors. Our EC flux measurements on Utö Island in the Baltic Sea show strong seasonal variation in marine VOC emissions, which can be coupled to the biomass and phenology of the phytoplankton as well as to environmental factors.

We highlight the emerging diversity of VOC emissions from aquatic ecosystems. These emissions need to be better quantified to assess their atmospheric fate and implications.

How to cite: Rinnan, R., Slater, E., Hughes, R., Qin, Y., Foroughan, M., Laurion, I., Chiapusio, G., Steinke, M., Laakso, L., Hellén, H., Kraft, K., Seppälä, J., Roslund, K., Riis Christiansen, J., and Holst, T.: Emerging diversity of volatile organic compounds from freshwater and marine ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15710, https://doi.org/10.5194/egusphere-egu25-15710, 2025.

Vegetation is the major source of volatile organic compounds (VOCs) in the atmosphere, which affect both air quality and climate. Long-term ecosystem-level data on biogenic VOC (BVOC) emissions, however, are limited. This limits assessment of impacts of short-term landscape-scale disturbances like clear-cutting, and seasonal-scale and interannual variation of emissions of boreal forests.

Here we present an overview of BVOC concentration and flux measurements and results spanning several years, leading up to the summer 2022 clear-cutting of a boreal forest located at the ICOS (Integrated Carbon Observation System) and ACTRIS (Aerosol, Clouds, and Traces Gases Research Infrastructure) station Norunda (located at 60°05′N, 17°29′E, ca. 30 km north of Uppsala) in Sweden. This managed boreal forest, between 80 and 120 years old, primarily consisted of a mix of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Beginning in summer 2020, BVOC mixing ratios were measured using a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus PTR-ToF-MS) (Tofwerk AG, Thun, Switzerland). These Vocus measurements (at 10 Hz) were collected at 35 m on the station flux tower to determine BVOC fluxes using the eddy-covariance method. During several intensive BVOC sampling periods in 2020 and 2022, hourly adsorbent samples were also collected, at 37 and 60 m, for subsequent GC-MS analysis to determine compound-speciated BVOC concentrations. These samples were additionally used to estimate the changes in the fluxes of speciated monoterpene (MT) compounds using the surface-layer-gradient (SLG) and modified Bowen-ratio (MBR) methods.

Our results indicate a large variety of VOC compounds being emitted by the forest system, including among them terpenoids - e.g., isoprene, monoterpenes (MTs) and sesquiterpenes (SQTs). The most common MT compounds emitted were α-pinene and Δ3-carene. During the 2022 clearcut, MT emissions increased by more than an order of magnitude during active-cutting, with persisting MT emission increases from clearcut residue which continued for several months. In comparison, many BVOCs lacking storage reservoirs in plant tissues (e.g., isoprene) were relatively unaffected by active-cutting. Fluxes and the mixture of speciated MT compounds observed before, during, and post-cut are compared, and the additional total and speciated MT emissions due to clear-cutting are estimated. For context, in Sweden 69% of total land cover is forest, of which 84% is productive forest for clear-cut forestry (~58% of total land cover). From Swedish forestry information of yearly absolute timber removal and on-site residue volumes following typical clearcuts, we find that current Swedish boreal forest MT emission inventory estimates may be significantly underestimated.

How to cite: Petersen, R., Wu, C., Mohr, C., Rinnan, R., Holst, T., Jaakkola, E., Krejci, R., and Rinne, J.: BVOC fluxes and concentrations at a boreal forest site in Sweden: an overview of long-term observations at ICOS Norunda and the impacts of forest clear-cutting on BVOC emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15481, https://doi.org/10.5194/egusphere-egu25-15481, 2025.

Earth system models have incrementally integrated the climate effects of biogenic volatile organic compounds (BVOCs). Currently, the global estimate stands at less than 1 PgC/year, considering only the emissions from actively growing plants while neglecting other sources of BVOCs and emissions from plants under stress.

Based on process understanding from various empirical data, this study extends beyond modelling plant BVOCs to include BVOC emissions from multiple ecosystem components, including litterfall, soil, forest management, and stress disturbance, into the dynamic vegetation model LPJ-GUESS. We will present four case studies in which these emissions are accounted for and compared with leaf constitutive emissions, highlighting their dynamic contributions to the ecosystem's total BVOC budget.

Furthermore, LPJ-GUESS previously simulated only isoprene and monoterpene emissions from plants, and this study further extends the model to consider all major BVOC compound groups (with a total of 150 compound species specified). We have dynamically coupled the LPJ-GUESS modelled BVOC emissions into the atmospheric chemistry and transport module TM5 within the European Earth System Model EC-Earth to assess the atmospheric impacts. We will also showcase the modelled impacts of BVOC emissions on atmospheric variables based on the coupled EC-Earth runs. The modelling framework provides an essential tool for integrating various ecosystem processes to understand BVOC emission dynamics and further assess the associated climate impact mechanically.

How to cite: Tang, J., van Noije, T., Wang, Z., Miller, P. A., Chen, Z., Bergkvist, J., Petersen, R., and Rinnan, R.: Beyond constitutive plant BVOCs: modelling emissions from litter, permafrost soil, forest management and stress disturbance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8986, https://doi.org/10.5194/egusphere-egu25-8986, 2025.

Biogenic Volatile Organic Compounds (BVOCs) are primarily emitted into the atmosphere by plants. These compounds serve various functions, including cellular protection and defense at the leaf level, chemical signaling between and within plants, and regulation of large-scale biogeochemical processes, such as influencing atmospheric chemistry and contributing to aerosol formation. The Amazon Forest is the major source of BVOCs to the global atmosphere.  Over the past four decades, multiple studies have measured BVOC concentrations in the air, mainly focusing on central Amazonia. However, while there is much to be investigated in undisturbed forests, the Amazon is already undergoing changes in land use and climate, particularly in the Amazon Arc of Deforestation. These changes may affect BVOC emissions and associated processes at the biosphere-atmosphere interface in ways that are not yet fully understood. In this light, this study aimed to identify and quantify the main BVOCs emitted by trees and crops in a changing Amazon region. We measured the above-canopy BVOC concentrations and leaf-level BVOC emissions from crops (cotton and corn) and dominant tree species in a mosaic of disturbed forest fragments and agricultural fields in southeastern Amazonia during the wet and dry seasons of 2023. Surprisingly, our results revealed that monoterpene and sesquiterpene emissions were higher than isoprene emissions for most trees and crops. When we compared the same tree species across a gradient of forest degradation, we found that monoterpene and sesquiterpene emissions were up to three times higher in the most degraded forest areas. Furthermore, with a leaf temperature curve experiment, we observed that at 45°C, the amount of recently assimilated carbon emitted in the form of isoprene, monoterpenes, and sesquiterpenes were up to 35%, 5%, and 23%, respectively - suggesting that plants were losing a high amount of carbon to cope with the heat stress. In contrast to leaf-level measurements, our ambient air measurements indicated that monoterpene and sesquiterpene concentrations were significantly lower than isoprene concentrations during both the wet and dry seasons, indicating that the atmosphere in this region is very reactive and that only leaf-level measurements are likely to give us a true measure of monoterpene and sesquiterpene emissions. Yet, interestingly, sesquiterpene concentrations were higher in the dry season than in the wet season, supporting the leaf-level results showing that increased heat and drought may lead to higher emissions of sesquiterpenes. This may have occurred either because plants emit more monoterpenes and sesquiterpenes in response to stress or due to changes in plant species composition resulting from forest degradation and land use changes. This study presents the first observations of BVOCs conducted in the Amazon Arc of Deforestation at both the leaf and canopy levels. The observed shift in emissions towards monoterpenes and sesquiterpenes is likely modifying atmospheric chemical and physical processes and the carbon balance in this already changing Amazon region. This makes it crucial to include these changes in air quality and Earth system modeling. 

How to cite: Gomes Alves, E., Robin, M., Maracahipes-Santos, L., Taylor, T., Faggiani, A. P., Silveiro da Silva, A. C., Nunes da Costa, D., Bendavid, N., Brando, P., Williams, J., Byron, J., Schüttler, J., and Hartmann, C.: Monoterpene and sesquiterpene emissions increase with forest degradation and land use change in the Amazon Arc of Deforestation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3769, https://doi.org/10.5194/egusphere-egu25-3769, 2025.

Biogenic volatile organic compounds (BVOC) are a highly complex and highly diverse set of chemicals emitted into the atmosphere by the Earth's biosphere. They affect atmospheric composition of trace gases such as the mixing ratios of methane, carbon monoxide, and tropospheric ozone through their atmospheric oxidation. Atmospheric oxidation products also lead to formation of atmospheric aerosol, which plays a crucial role in defining Earth's radiative balance and impacts air quality.  

Further increases in the average global temperature are expected for the following decades, with warmer and dryer conditions for Alpine regions. Warm winters appear to lead to earlier leaf-out. This may put trees at higher risk of late frost in spring. Thus, in addition to long-term changes in abiotic factors (temperature, water availability), the frequency of stress and double-stress events, such as a late spring frost and an extreme summer drought occurring in the same year, is expected to increase. How trees respond to such changes in abiotic factors and to abiotic (double) stress regarding their BVOC emissions composition and quantities is critical in understanding how atmospheric chemistry and SOA properties may be impacted.  

During the summer of 2022, we studied the impact of elevated temperatures (heat), reduced water availability (drought), extreme events (early spring frost) and double stress (early spring frost followed by extreme summer drought) on tree seedlings i.) BVOC precursors in plant tissues (i.e., secondary metabolites) and ii.) BVOC gas-phase emissions. To this end, i.) we developed an analytical method for extraction and chromatographic separation of secondary metabolites from plant tissues, and ii.) we 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 will present comprehensive results from experiments with Scots Pine, Beech, and Oak seedlings under various abiotic stress conditions. Our findings provide crucial insights for improving estimations of future BVOC emissions and their atmospheric impacts.

How to cite: Pieber, S. M., Molteni, U., Luo, N., Kalberer, M., Faiola, C., and Gessler, A.: Plant volatile emissions experiments with coniferous and broadleaf tree seedlings: the impact of extreme events and future climate scenarios, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16045, https://doi.org/10.5194/egusphere-egu25-16045, 2025.

Recent research at Whiteface Mountain, one of the few remaining sites in the U.S. where long-term cloud water chemistry research has continued to the present day, has revealed a doubling in cloud water organic carbon concentrations since measurements began in 2009. This dramatic increasing trend was an unexpected result, which requires further investigation. The present study attempts to verify these results using additional independent datasets from within the region and explores potential driving factors behind the observed organic carbon trends. Through evaluation of measurements from four additional sites in the north eastern U.S., each with long-term measurements of organic carbon concentrations within bulk cloud water or wet deposition samples, we show that there is strong evidence for a regional increasing trend in organic concentrations within aqueous atmospheric samples. These results provide further context behind the growing inorganic ion imbalance observed in wet deposition samples collected across the eastern U.S. and Canada, as identified in a separate study published in 2021. We discuss hypotheses for the potential driving factors behind the increasing organic carbon trends observed, including increased biomass burning influence, increased biogenic emissions and a changing chemical regime characterized by relatively high concentrations of reactive nitrogen chemical species.

How to cite: Lance, S., Lawrence, C., Tripathy, A., Casson, P., Snyder, P., Murray, G., Murray, D., Wymore, A., McDowell, B., Shattuck, M., Shanley, J., Campbell, J., Green, M., Apel, E., Hornbrook, R., Hills, A., Yerger, E., and Kelting, D.: Long-term Trends in Organic Carbon Concentrations within Cloud Water and Precipitation Samples in the Northeastern United States , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13574, https://doi.org/10.5194/egusphere-egu25-13574, 2025.

The chemical diversity in the varied spectrum of atmospheric trace gases requires to combine different ionization approaches to enable comprehensive mass spectrometric analysis. Ion-molecule reactors (IMR) at high pressure generally enable better detection limits, due to a larger reaction time, but are also more prone to matrix effects (e.g., dependency on humidity). For the ionization of low polarity volatile organic compounds (VOCs), positive mode chemical ionization (e.g. PTR, low IMR pressure) has been found to be more suitable than negative mode ionization (e.g., NO₃^-, I^-, Br^-), but humidity dependency and other matrix effects of unselective reagent ions need to be constrained e.g. by reduction of IMR pressure. More selective reagent ions such as ammonium and aminium have been previously proposed for more sensitive and soft ionization. However, they are reactive, toxic, and difficult to control.

Inspired by these challenges, we demonstrate uronium as an efficient and robust reagent cation for the ionization of VOCs at high IMR pressures. Urea, a solid chemical safe to humans with a negligible vapor pressure under normal circumstances, is sublimated from the solid phase under x-ray irradiation, which also subsequently forms the uronium ion. We determine the calibration factors for VOCs, amines, and DMSO under different humidities in calibration experiments, interpret the ionization efficiencies using theory, and show results of test measurements of different chemical systems. Beyond the favorable sensitivities allowing detection at the low ppq level - attainable due to uronium’s applicability at high IMR pressure and a tendency to form remarkably strongly bound ion-molecule clusters – and low susceptibility to humidity changes, the marked benefit of uronium CIMS lies in the trivial handling of the reagent supply and long-term stability of the ion production system. The combination of favorable performance and easy handling render uronium CIMS promising to become a go-to method for ultra-sensitive positive mode chemical ionization.

How to cite: Finkenzeller, H., Shcherbinin, A., Vinkvist, N., Jost, H.-J., Partovi, F., Mikkilä, J., Kontro, J., Sarnela, N., Kangasluoma, J., and Rissanen, M.: Uronium CIMS: Robust high-pressure positive mode ion attachment chemical ionization mass spectrometry via X-ray-assisted sublimation of urea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8957, https://doi.org/10.5194/egusphere-egu25-8957, 2025.

Volatile Organic Compounds (VOCs), emitted by both biogenic and anthropogenic sources, play a crucial role in atmospheric processes and significantly affect air quality. Despite their importance, routine monitoring of VOCs poses challenges due to limitations in time-resolution, labor intensity, long-term stability, and compound-specific identification capabilities. Proton-transfer-reaction mass-spectrometry (PTR-MS) is widely used for detecting VOCs with high time-resolution and stability. However, as a soft chemical ionization method, it primarily identifies chemical compositions rather than specific compounds. Acquiring additional chemical information through alternative ionization methods remains labor-intensive, making it impractical for long-term VOC monitoring.

Here, we introduce an innovative solution to streamline these time-consuming tasks with the push of a button for key atmospheric VOCs. This new VOC monitor “VOCentinel” leverages Selective-Reagent-Ion (SRI) PTR-MS combined with Automatic Measurement and Evaluation (AME), integrating recent technological advancements in PTR-MS, such as fast switching of reagent ions, extended volatility range (EVR) surface treatment, active humidity control, and automatic pattern matching, alongside IONICON's extensive experience in robust industrial monitoring. Essentially, five ionization modes sequentially ionize specific atmospheric VOCs within one minute, and the resulting mass spectra are immediately analyzed for chemical composition using a pattern matching algorithm. Automatic quality control ensures optimal instrument performance.

We will present a comprehensive characterization of the VOCentinel, emphasizing its long-term stability, and share initial results from VOC measurements in Innsbruck, Austria. Using isoprene as an example - an important biogenically emitted VOC often subject to chemical interferences in PTR-MS measurements - we demonstrate the system’s ability to automatically measure, evaluate, and correctly quantify compounds with isobaric and/or isomeric interferences.

How to cite: Müller, M., Winkler, K., Herburger, A., Graus, M., and Herbig, J.: VOCentinel - a novel solution for automated real-time monitoring of atmospheric VOCs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9860, https://doi.org/10.5194/egusphere-egu25-9860, 2025.

In recent years, there has been increasing interest in monitoring Volatile Organic Compounds (VOCs) in the ambient atmosphere. VOCs in the atmosphere can lead to dangerous levels of ozone, impacting human health and degrading ecosystems. Further, many VOCs are themselves considered highly toxic at parts-per-billion (ppb) and even parts-per-trillion (ppt) levels, potentially causing respiratory problems and contributing to elevated cancer risk in affected populations. More recently, the EPA has proposed more stringent fence line monitoring requirements for six critical air toxics: benzene, ethylene oxide, chloroprene, 1,3-butadiene, vinyl chloride, and ethylene dichloride.

In response to this growing need for high-performance, field-deployable VOC analyzers, Picarro has developed Broad Band Cavity Ring-Down Spectroscopy (BB-CRDS), a laser-based technology that is capable of quantifying a wide variety of VOCs in real time (< 5 seconds) at ppb and ppt levels. This analyzer is capable of simultaneously measuring ten or more compounds, selected from our growing library of nearly 500 characterized species, which includes both VOCs and common inorganics like H₂O, CO₂, CH₄, N₂O, and NH₃. It is simple to operate, and it can be deployed in harsh environments with little to no consumables. We demonstrate the design and performance of these analyzers, presenting substantial advancements for air quality management and regulatory compliance.

How to cite: Wozniak, J., Drori, K., Chedgy, R., Rella, C., Skog, K., and Lucic, G.: Advancements in the Detection and Monitoring of VOCs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13080, https://doi.org/10.5194/egusphere-egu25-13080, 2025.