Europe is one of the most studied areas related to biogenic volatile organic compound (BVOC) emissions. However, our knowledge of these atmospheric reactive compounds is still quite limited even there. Total hydroxyl radical (OH) reactivity studies indicate that half of the atmospheric reactive compounds are still unknown especially in the forested areas (Yang et al. 2016) and OH and ozone reactivity studies of our group have shown high fractions of reactivity from biogenic emissions (Praplan et al. 2020 and Thomas et al. 2023).

Globally, isoprene is the primary emitted BVOC. While boreal forests in Northern Europe are mainly considered as monoterpene emitters, Central Europe is expected to be dominated by isoprene (e.g. Messina et al. 2016). However, our results from a campaign at 17 stations over Europe in summer 2022 indicated that BVOC mixing ratios are highly variable and some areas also in Central Europe may be dominated by monoterpenes.

Sesquiterpenes and diterpenes have very high potential for secondary organic aerosol formation, but much less is known on their emissions and atmospheric concentrations. Our studies show that birches and spruces may be strong sesquiterpene emitters. We have also found that some urban trees in Montreal and wetlands in Lapland known as isoprene emitters may also release significant amounts of sesquiterpenes. Additionally, forest floor represents a potential source of sesquiterpenes.

Compared to terrestrial sources very little is known on the marine emissions of BVOCs. There are studies on dimethyl sulphide, but our recent results on an island in Baltic Sea suggest that other sulphuric compounds, like methanethiol, may be important too and could have strong impacts on SO₂ production and therefore also on new particle and cloud formation. Furthermore, our recent campaign at the coast of Baltic Sea indicates that phytoplankton and macrophytes could be a source of isoprene and monoterpenes (Thakur et al., 2024 publication under prep).

Compounds classified as BVOCs (e.g. monoterpenes) can also be emitted from anthropogenic sources, such as construction sites (e.g. from wooden material), as well as cleaning and personal care products. Our studies in a street canyon in Helsinki in 2022 indicates that they strongly impact local atmospheric chemistry even in wintertime.

Messina, P., Lathière, J., Sindelarova, K., Vuichard, N., Granier, C., Ghattas, J., Cozic, A., and Hauglustaine, D. A.: Global biogenic volatile organic compound emissions in the ORCHIDEE and MEGAN models and sensitivity to key parameters, Atmos. Chem. Phys., 16, 14169–14202, https://doi.org/10.5194/acp-16-14169-2016, 2016

Praplan, A. P., Tykkä, T., Schallhart, S., Tarvainen, V., Bäck, J., and Hellén, H.: OH reactivity from the emissions of different tree species: investigating the missing reactivity in a boreal forest, Biogeosciences, 17, 4681–4705, https://doi.org/10.5194/bg-17-4681-2020, 2020.

Thomas, S. J., Tykkä, T., Hellén, H., Bianchi, F., and Praplan, A. P.: Undetected biogenic volatile organic compounds from Norway spruce drive total ozone reactivity measurements, Atmos. Chem. Phys., 23, 14627–14642, https://doi.org/10.5194/acp-23-14627-2023, 2023.

Yang, Y., Shao, M., Wang, X., Nölscher, A. C., Kessel, S., Guenther, A., and Williams, J.: Towards a quantitative understanding of total OH reactivity: A review, Atmos. Environ., 134, 147–161, https://doi.org/10.1016/j.atmosenv.2016.03.010, 2016.

How to cite: Hellén, H., Tykkä, T., Schallhart, S., Thomas, S., Aas, W., Wegener, R., Salameh, T., Rissanen, K., Thakur, R., Losoi, M., Laakso, L., Seppälä, J., Kraft, K., Hakola, H., and Praplan, A.: Understudied BVOC emissions in Europe and their potential atmospheric impacts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5216, https://doi.org/10.5194/egusphere-egu24-5216, 2024.

Monoterpenes (C10H16) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year−1), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth’s radiative budget and, thereby, climate change[1-3]. Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (−) forms are rarely distinguished in measurement or modelling studies[4-6]. Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood. Here we present enantiomerically separated atmospheric monoterpene and isoprene data from an enclosed tropical rainforest ecosystem in the absence of ultraviolet light and atmospheric oxidation chemistry, during a four-month controlled drought and rewetting experiment, the Biosphere 2 Water, Air and Life Dynamics campaign (B2WALD) in 2019[7, 8]. The measurements were obtained with an on-line gas chromatograph-mass spectrometer over five time periods: pre-drought, early drought, severe drought, deep rewet and rain rewet.

Surprisingly, the emitted enantiomers showed distinct diel emission peaks, which responded differently to progressive drying. Isotopic labelling established that vegetation emitted mainly de novo-synthesized (−)-α-pinene, whereas (+)-α-pinene was emitted from storage pools. As drought progressed, the source of (−)-α-pinene emissions shifted to storage pools which would favour cloud formation since the peak concentration became more aligned with temperature. Pre-drought mixing ratios of both α-pinene enantiomers correlated better with other monoterpenes than with each other, indicating different enzymatic controls. These results show that enantiomeric distribution is key to understanding the underlying processes driving monoterpene emissions from forest ecosystems and predicting atmospheric feedbacks in response to climate change.

1. Jokinen, T., et al., Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications. Proceedings of the National Academy of Sciences, 2015. 112(23): p. 7123-7128.

2. Engelhart, G.J., et al., CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol. Atmos. Chem. Phys., 2008. 8(14): p. 3937-3949.

3. Laothawornkitkul, J., et al., Biogenic volatile organic compounds in the Earth system. New Phytologist, 2009. 183(1): p. 27-51.

4. Yáñez-Serrano, A.M., et al., Monoterpene chemical speciation in a tropical rainforest:variation with season, height, and time of dayat the Amazon Tall Tower Observatory (ATTO). Atmos. Chem. Phys., 2018. 18(5): p. 3403-3418.

5. Jardine, K.J., et al., Monoterpene 'thermometer' of tropical forest-atmosphere response to climate warming. Plant Cell Environ, 2017. 40(3): p. 441-452.

6. Guenther, A., et al., The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2. 1): an extended and updated framework for modeling biogenic emissions. 2012.

7. Byron, J., et al., Chiral monoterpenes reveal forest emission mechanisms and drought responses. Nature, 2022. 609(7926): p. 307-312.

8. Werner, C., et al., Ecosystem fluxes during drought and recovery in an experimental forest. Science, 2021. 374(6574): p. 1514-1518.

How to cite: Byron, J., Kreuzwieser, J., Purser, G., van Haren, J., Ladd, S. N., Meredith, L., Werner, C., and Williams, J.: Changes in chiral monoterpenes during drought in a rainforest reveal distinct source mechanisms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13774, https://doi.org/10.5194/egusphere-egu24-13774, 2024.

Biogenic volatile organic compounds (BVOCs) play an essential role in tropospheric chemistry, forming secondary organic aerosol and influencing ambient ozone. Since particles produced from BVOCs may grow to form cloud condensation nuclei (CCN) and influence cloud properties, BVOCs also indirectly affect the global radiation budget. The terrestrial biosphere is a significant source of BVOCs, with the emissions from the tropical forests (mainly the Amazon) contributing about 80% to the global BVOC budgets. Our understanding of BVOC emissions and chemistry, particularly their role in particle formation over the Amazon rainforest, is incomplete. Therefore, a comprehensive suite of atmospheric instruments was used to measure BVOCs, particles and other trace gases over the Amazon rainforest using the High Altitude and Long-range Observation (HALO) aircraft from Dec 2022 to Jan 2023. The main focus of the field campaign was to investigate how tropical convection affects the atmospheric chemistry of BVOCs using measurements made from 300m to 15km altitude. The measurements of BVOCs were performed using PTR-ToF-MS and fast GC-MS.

 Isoprene was found to be the dominant BVOCs in the Amazon boundary layer. Interestingly, as a result of the regional strong convection, we observed elevated mixing ratios of isoprene (>1ppb), its oxidation products, and the sum of monoterpenes (MTs) in the upper troposphere (~10-12 km). This shows that despite the fast reaction rate of isoprene with OH (lifetime 1 hour) significant amounts can reach the outflow regions of the upper troposphere. The diel (24-hour) profile of isoprene mixing ratios, its oxidation products, and MTs in the upper troposphere were observed to change markedly with altitude. Near the surface (300m) BVOC emissions including isoprene varied with light and temperature peaking at circa 13:00 local time. However, between 10-12km, isoprene mixing ratios rose during the night and peaked before dawn and the onset of photochemical oxidation. This suggests that the nocturnal convection of residual isoprene is an effective vertical transport mechanism that primes the upper troposphere for particle production the following day. The boundary layer isoprene mixing ratios were also found to vary spatially with the strongest gradient found between the forested and deforested regions. The mean mixing ratios of isoprene (2.96 ±0.72 ppbv) and MTs (0.31±0.09 ppbv) in the forested regions were ~4 times higher than their values measured in the deforested regions. In both the boundary layer and outflow regions of the tropical Amazonian troposphere isoprene is a key player in the atmospheric chemistry. Preliminary results of the spatio-temporal variation and vertical profiles of other selected BVOCs will be presented.

How to cite: Tripathi, N., Edtbauer, A., Wang, N., Ringsdorf, A., Krumm, B., Klüpfel, T., Lelieveld, J., and Williams, J.: Impact of deep convection on biogenic volatile organic compounds in the upper troposphere over the Amazon Rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3572, https://doi.org/10.5194/egusphere-egu24-3572, 2024.

For accurate prediction and modelling of air quality and climate, it is necessary to understand the emissions of volatile organic compounds (VOCs) from the potpourri of sources that they are emitted from: traffic, industry, households, plants, agriculture, etc. In the past, efforts to understand the magnitude and composition of VOC emissions have often relied on indirect methods – either using bottom-up emission models, or inferring emissions top-down from concentration measurements via chemical transport models. Both approaches rely on a number of assumptions regarding chemical reactions and transport - and thus are subject to large uncertainties.

Airborne flux observations provide direct emission and deposition information at landscape scale with a resolution of a few km. We performed airborne eddy covariance measurements of a large range of VOCs on board a Twin Otter aircraft in Los Angeles and the agricultural San Joaquin Valley in California using PTR-ToF-MS. Combining these observations with a footprint model, we matched them with gridded inventories in space and time. The comparison with the inventories showed a good representation of typical traffic VOCs, but a significant underestimation of oxygenated VOCs (likely from volatile chemical products and cooking) and terpenoids by the inventories.

Using airborne flux footprints in combination with landcover information of the San Joaquin Valley, we disaggregated the observed VOC emissions by multivariate linear regression and attributed them to their sources. This way, we obtained typical VOC emission rates and composition for dairy farms, citrus crops, citrus processing facilities, oak forests, oil and gas wells, and urban areas.

How to cite: Pfannerstill, E. Y., Arata, C., Zhu, Q., Schulze, B. C., Woods, R., Harkins, C., Schwantes, R. H., McDonald, B. C., Seinfeld, J. H., Bucholtz, A., Cohen, R. C., and Goldstein, A. H.: Airborne flux measurements for validation of VOC emission inventories and source attribution , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1318, https://doi.org/10.5194/egusphere-egu24-1318, 2024.

Volatile organic compounds (VOCs) together with nitrogen oxides contribute to the formation of ground-level ozone as well as PM_2.5 pollution through secondary organic aerosol formation, with adverse effects on human health and environment. Researchers have mainly focused on quantifying VOC emissions from plant canopies and their controls, leading to improvements in atmospheric chemistry models (Jimenez et al., 2009). However, much less attention has been spent on quantifying dry deposition of primary and secondary VOCs to surfaces, with most models often using deposition rates extrapolated from SO₂ (as a proxy of a water-soluble gas of limited reactivity) and O₃ (as a proxy of an insoluble reactive gas), making uncertain assumptions on the relative behaviour of key VOCs (Wesely, 2007). To address this, we conducted the first systematic, measurement-based investigation into VOC dry deposition as part of the ‘Dry Deposition Processes of VOCs’ project funded by Natural Environment Research Council. The overarching aim of the study was to reduce uncertainty in atmospheric chemistry models by developing parameterisations for the dry deposition of VOCs. The preliminary results of our laboratory study on plant fumigation with methacrolein (MACR), among other selected VOCs, are presented here.

An automated dynamic gas-exchange chamber system was developed to expose test plants to specific VOCs at various concentrations under controlled conditions. Overall, six plant species (see below) were tested with each experiment lasting four days: one day to observe background emissions and three days with VOC fumigation at 20, 15 and 10 °C. Three levels of relative humidity (RH) were applied during day and night times, being fumigated with five concentrations of VOCs within each RH level. In total, eleven VOCs were selected for fumigation: water-insoluble (isoprene, benzene, toluene, xylene, a-pinene) and water-soluble (methanol, acetonitrile, acetaldehyde, acetone, acetic acid and MACR). VOCs were measured using a proton transfer reaction instrument equipped with time-of-flight mass spectrometer (PTR-Qi-TOF). Fluxes were calculated based on concentration difference between blank and measurement chambers and then normalized by the corresponding plant leaf area indices.

MACR appears to be ‘valuable’ VOC to study dry deposition as it is not typically emitted by plants but is an important first-order product of isoprene oxidation in the atmosphere. Nevertheless, minor MACR emissions have been reported, suggesting that oxidation may also take place within leaves (Fares et al., 2015).   

The deposition velocity of MACR was found to increase with RH, and larger deposition velocities were consistently observed during the daytime compared to the night. This diurnal dependence indicates either stomatal control or photochemical processes, or a combination of the two, were present under daylight conditions. However, this varied substantially across tested plants being ranked in the following order Pinus sylvestris > Hedera sp. > Picea glauca > Betula sp. > Tsuga heterophylla > Ilex aquifolium. At all times, MACR compensation points were found to be negligible (near zero) or even negative, suggesting minor or no impact on deposition rates.

These findings are enhancing our understanding of VOC deposition and will inform the development of new parameterizations for atmospheric chemistry models.

How to cite: Medinets, S., Langford, B., Di Marco, C., Vieno, M., and Nemitz, E.: Humidity-dependent dry deposition of methacrolein to plant species, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11361, https://doi.org/10.5194/egusphere-egu24-11361, 2024.

Gas-phase biogenic organosulfur compounds, and their oxidation products are important for the formation and growth of aerosol in the marine environment. During the spring-summer increase in marine biological activity in the northern hemisphere, dimethyl sulfide ((CH₃)₂S, DMS) and methanethiol (CH₃SH, MeSH) are emitted from ocean and sea-ice environments. The emission or transport, and following oxidation, of organosulfur compounds to the Arctic marine environment impacts the available aerosol number and cloud condensation nuclei. Here, we examine organosulfur compound composition, atmospheric fate, and relationships to the aerosol population at the onset of sea-ice melt.

We present shipborne gas-phase measurements of reduced and oxidized organosulfur compounds made with a H­₃O⁺/NH₄⁺ reagent ion switching chemical ionization time-of-flight mass spectrometer as part of the Atmospheric Rivers and the onseT of sea ice MELT (ARTofMELT) campaign on IB Oden. Our measurements during ARTofMELT spanned from May 7^th to June 15^th of 2023 and took place over pack ice and the marginal ice zone between 78 and 81°N between the east coast of Greenland and the Svalbard archipelago (the Fram Strait). Non-DMS organosulfur species made a significant contribution to atmospheric sulfur during the campaign. MeSH was present at concentrations ~10% of DMS (10’s of ppt_v) during periods of elevated organosulfur compounds (DMS exceeding ~100 ppt_v) and was correlated with DMS (R² > 0.8). Ambient temperatures ranged between -15 and 2°C, making the primary oxidation reaction between DMS and the hydroxyl radical the OH-addition pathway to produce dimethyl sulfoxide (DMSO). We observed DMSO in concentrations occasionally exceeding 150 ppt_v, and the chemical formula C₂H₆SO₂ (likely dimethyl sulfone) at similar concentrations to DMSO. During low ozone periods (< 10 ppb_v), the loss of DMS was potentially influenced by halogen chemistry resulting in an increased abundance of DMSO relative to DMS. We use our measurements to investigate organosulfur compound composition and loss pathways under a variety of atmospheric conditions.

How to cite: Willis, M., Zang, C., Asplund, J., Mattsson, F., Zieger, P., and Tjernström, M.: Biogenic sulfur compounds and their oxidation products in the spring-to-summer Arctic marine atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11383, https://doi.org/10.5194/egusphere-egu24-11383, 2024.

The oxidation of dimethyl sulfide (DMS) leads to the formation of sulfuric acid (SA) and methane sulfonic acid (MSA), which has a great impact on atmospheric aerosol and cloud formation (Barnes, Hjorth et al. 2006). Despite the great importance, the formation mechanism of MSA from DMS has remained unclear for decades (Shen, Scholz et al. 2022).

           The reaction of DMS with OH radical forms methanesulfinic acid (MSIA), methane sulfenic acid (MSEA), methylation radical (CH₃S) radical, and hydroperoxymethyl thioformate (HPMTF)(Berndt, Scholz et al. 2019, Shen, Scholz et al. 2022). Among them, the oxidation of the first three all undergoes either the CH₃SO radical or the CH₃SO₂ radical as intermediates(Kukui, Borissenko et al. 2003, Berndt, Chen et al. 2020, Chen, Berndt et al. 2021).

           We theoretically investigated the atmospheric fate of the CH₃SO and CH₃SO₂ radicals. The results suggest that CH₃SO radical mainly reacts bimolecularly forming CH₃SO₂, and the CH₃SO₂ radical either decomposes forming SO₂ or adds O₂ forming the peroxy radical CH₃S(O)₂OO in the atmosphere. We show that the branching ratio of SO₂ and CH₃S(O)₂OO formation from CH₃SO₂ is temperature sensitive, and the ratio of SO₂ to CH₃S(O)₂OO decreases from about 99:1 to about 95:5 when reducing the temperature from 300 K to 260K. The peroxy radical CH₃S(O)₂OO can react bimolecularly forming the CH₃SO₃ intermediate, which can abstract an H from HO2 forming MSA. In addition, we show that MSA can also form directly via the reaction of MSIA and OH followed by O₂ addition (Chen, Lane et al. 2023).

           Our study indicates that temperature may play a crucial role in explaining atmosphere MSA formation. SO₂ is likely the dominant product from DMS + OH in the tropics and warm regions, while in the colder and polar regions, large amounts of MSA can be formed in the gas phase by DMS reacting with OH. Global modeling indicates that the proposed temperature-sensitive MSA formation mechanism leads to a substantial increase in the simulated global atmospheric MSA formation and burden (Chen, Lane et al. 2023).

How to cite: Chen, J., Lane, J. R., Bates, K. H., and Kjaergaard, H. G.: Atmospheric Gas Phase Formation Mechanism of Methanesulfonic Acid, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3112, https://doi.org/10.5194/egusphere-egu24-3112, 2024.

Among the regulated sources of pollutants, shipping has a significant contribution to NO_x and SO₂ global emissions ^1–3. The international maritime transport regulation was updated in 2020 lowering the sulphur content in marine fuel globally from 3.5% to a maximum of 0.5% (m/m). Specific Sulphur Emission Control Areas have been established where the emissions of sulphur are further restricted, such as the Channel, between France and the U.K. However, other pollutants such as Volatile Organic Compounds (VOC) or Particulate Matter (PM), are not regulated in terms of shipping emissions. VOCs are of particular importance in the atmospheric chemistry processes, especially because of their role in the formation of ozone and as precursors of secondary PM in the vicinity of densely populated coastal areas ⁴. This raises the question of which VOC are emitted by ships under these new emission standards, what their emission rates are and what their impact on air quality is? Only a few studies considered the speciation of VOC emitted by ships ⁵, yet those data are crucial for reliable gas-phase atmospheric chemistry modelling and correct impact assessment. Our study presents the analysis of a VOC dataset collected during an intensive one-month field campaign in the harbour of Dunkirk in northern France, the third largest French port. The observations were conducted on a site near ferry and cargo terminals and provided high temporal resolution measurements of VOCs, using a PTR-ToF-MS, alongside many other parameters (meteorology, particles, gases). Data analysis allowed the identification of more than 65 plumes from different ferries, based on a methodology that relies on favourable meteorological conditions, port office entries and tracers like SO₂. Firstly, Emission Factors (EFs) have been calculated, providing an estimate of the relative amount of a pollutant emitted relative to CO₂. For species like SO₂ or CH₄, our results were consistent with the EMEP emission inventory of 2021 (De Lauretis et al. 2021), however, some VOCs displayed large differences compared to ship exhaust determined EF within the EU/SCIPPER project ⁷. As an example, the median EF of benzene ions (C₆H₆.H⁺) was 27.87 mg/kg(fuel) versus 5.31 mg/kg(fuel) for SCIPPER, whereas toluene (C₇H₈.H⁺) was 23.37 mg/kg(fuel) versus 0.49 mg/kg(fuel) for exhaust measurement. Secondly, Positive Matrix Factorization has been applied to the dataset to investigate a shipping chemical profile of VOC that will allow us to calculate the contribution of shipping emission to the total VOC concentration in such harbour area.

1. Corbett, J. J. et al. Environ. Sci. Technol. 41, 8512–8518 (2007).

2. Faber, J., Hanayama, S., Zhang, S. & Pereda, P. Fourth IMO GHG Study 2020 Executive-Summary. (2020).

3. Merk, O. Shipping Emissions in Ports. vol. 2014/2 (2014).

4. Fang, H. et al. Journal of Geophysical Research: Atmospheres 127, e2022JD037301 (2022).

5. Xiao, Q. et al. Atmos. Chem. Phys. 18, 9527–9545 (2018).

6. De Lauretis, R., Ntziachristos, L. & Trozzi, C. Air pollutant emission inventory guidebook 2019, update 2021. (2021).

7. Timonen, H. et al. Ship on-board emissions characterisation. (2022).

How to cite: Volent, E., Tinel, L., F. de Brito, J., Jamar, M., and Sauvage, S.: Volatile Organic Compounds shipping emissions observed in an industrial harbour of northern France , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9501, https://doi.org/10.5194/egusphere-egu24-9501, 2024.

Development of a molecular-level understanding of the processes governing the evolution of organic aerosol mass has been a long running challenge. I will present new insights into the potential for biogenic volatile organic compounds (BVOC) to form new particles and contribute to organic aerosol formation. Specifically, I will illustrate the coupled roles of organic peroxy radical chemistry and shallow and deep convective clouds in transporting or processing BVOC and their oxidations products that impact aerosol particle formation and growth on scales that are typically unresolved in global scale chemical transport models. The fate of organic peroxy radicals from BVOC depends upon NO_x, with natural and anthropogenic sources, as well as temperature and therefore changes substantially with both altitude and region. Deep convection efficiently transports BVOC to the upper troposphere with significant decreases in temperature and, over land substantial NO_x from lightning and from co-transport of polluted boundary layer air. The fates of BVOC-derived organic peroxy radicals in the upper troposphere will therefore occur in conditions rarely probed experimentally, with implications for the formation of low volatility products. In addition, during transport through shallow or deep convective clouds, soluble BVOC oxidation products commonly considered important precursors to secondary organic aerosol (SOA) will partition and potentially react in the cloud water. Thus, the common occurrence of both shallow cumulus and deep convective clouds is a large but poorly represented lever on biogenic SOA formation. 

I will show results from studies of the above processes using a hierarchy of models, including parcel models run along trajectories from Large Eddy Simulation (LES) models of deep convective clouds, LES models of cumulus-topped boundary layers with online multi-phase chemistry, and global chemical transport simulations with online chemistry and implications for new particle formation and organic aerosol mass budgets. Chemical mechanisms are informed by recent laboratory studies of organic peroxy radicals, such as autoxidation, accretion product formation from cross-reactions, and organic nitrate formation, as well as the aqueous chemistry of isoprene-derived epoxy diols. Comparisons of these models to observations reveal the importance of scattered cumulus clouds to the fate of isoprene epoxy diols and thus its SOA formation potential, the role of lightning and soil NO_x in new particle formation from BVOC oxidation in the upper-tropospheric outflow of deep convective clouds, and the potential for isoprene oxidation at high NO and low temperature to serve as a key source of low volatility organics that drive new particle formation in deep convective outflow.

How to cite: Thornton, J.: Biogenic VOC Multiphase Chemistry – From Cloud Scavenging to New Particle Formation  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2952, https://doi.org/10.5194/egusphere-egu24-2952, 2024.

Secondary organic aerosol (SOA), formed by oxidation of volatile organic compounds, significantly influence air quality and climate. Biogenic highly oxygenated organic molecules (HOM), particularly those formed from monoterpenes, play a key role in SOA formation and growth. As the most important daytime oxidant, hydroxyl radical (OH•) initiated HOM from monoterpenes is believed to be mainly formed via OH addition channel. However, for α-pinene and limonene, we found that the contribution of hydrogen abstraction channel by OH contribute a significantly to HOM formation. We will present our observations and theoretical calculations, showing the role of hydrogen-abstraction and alkoxy radicals for fast autoxidation leading to HOM formation. We also provide formation mechanisms of and yields of HOM, suggesting the non-negligible contribution of the hydrogen abstraction channel to ambient SOA, particularly in OH-rich areas.

How to cite: Zhao, D., Shen, H., Luo, H., Luc, V., Kang, S., Iida, P., Fuchs, H., Hallquist, M., Wahner, A., Kiendler-Scharr, A., and Mentel, T.: Significance of hydrogen abstraction in the formation of highly oxygenated organic molecules in the OH oxidation of monoterpenes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20198, https://doi.org/10.5194/egusphere-egu24-20198, 2024.

Monoterpenes, comprising 15% of global biogenic volatile organic compound emissions, play a pivotal role in atmospheric chemistry. ∆³-carene, the second most prevalent monoterpene, has been identified as a significant source of secondary organic aerosol (SOA) upon oxidation, potentially surpassing α-pinene under similar conditions. Despite its importance, research has predominantly focused on α-pinene , leaving gaps in our understanding of ∆³-carene's oxidation pathways, particularly its capacity to form highly oxygenated organic molecules (HOM).

To address this knowledge gap, we conducted an investigation into HOM formation during the ozonolysis of ∆³-carene using atmospheric simulation chambers. Employing a chemical ionization atmospheric pressure interface time-of-flight mass spectrometer with nitrate as the reagent ion (NO3-CIMS), we measured HOM resulting from ∆³-carene ozonolysis. Additionally, we explored the impact of temperature and relative humidity on HOM composition and distribution across various conditions (0, 10, and 20 ºC, and humidity levels below 15% and around 80%).

Our analysis revealed diverse HOM monomers and dimers from ∆³-carene ozonolysis. Predominant HOM monomers included C₁₀H_14,16O₉ and C₉H_12,14O₉, while the largest dimers comprised C₁₉H₃₀O_6,10,11 and C₂₀H₃₂O_7,9,11. Significantly, HOM monomers with 9 or more oxygen atoms and all dimers irreversibly condensed onto particles, while those with 6-8 oxygen atoms behaved as semi-volatile organic species, maintaining notable gas-phase concentrations. Intriguingly, ∆³-carene ozonolysis produced higher HOM concentrations than α-pinene, suggesting distinct formation pathways for these two monoterpenes. Furthermore, we observed a substantial decrease in HOM concentrations at lower temperatures, consistent with previous studies on α-pinene ozonolysis. Despite similar main HOM species at temperatures of 20, 10, and 0 ℃, the ratio of HOM dimers to monomers increased from 0.78 to 1.51 as temperatures decreased. This temperature-dependent variation underscores the complexity of ∆³-carene's atmospheric processing, revealing nuanced behaviors of HOM under different environmental conditions.

In conclusion, this study provides valuable insights into the HOM formation pathways of ∆³-carene, shedding light on its unique atmospheric chemistry. The observed differences in HOM concentrations and temperature-dependent behaviors highlight the need for a more comprehensive understanding of various monoterpenes, moving beyond the well-studied α-pinene. These findings contribute to the broader knowledge of biogenic volatile organic compounds and their impact on atmospheric processes.

How to cite: Luo, Y., Thomsen, D., Iversen, E. M., Roldin, P., Skønager, J. T., Li, L., Priestley, M., Pedersen, H. B., Hallquist, M., Bilde, M., Glasius, M., and Ehn, M.: Formation and temperature dependence of Highly Oxygenated Organic Molecules from ∆3-carene ozonolysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7707, https://doi.org/10.5194/egusphere-egu24-7707, 2024.

Aromatic compounds like xylene contribute significantly to the formation of tropospheric secondary organic aerosol (SOA) that have strong implications on health and on climate. The sources of this class of molecules are primarily anthropogenic, but biogenic sources of aromatics can be significant too. To form SOA, the volatile xylene needs to oxidize into low volatility aerosol precursors with multiple oxygen containing polar functional groups called highly oxygenated organic molecules (HOMs). It does this through the autoxidation mechanism, which is a sequential process involving peroxy radicals where each intra-molecular reaction step such as an H-atom shift is followed quickly by O₂ addition. While laboratory measurements using the sensitive chemical ionization mass spectrometer (CIMS) instrument indicate rapid conversion of xylene to HOM, this is unsupported by established oxidation mechanisms. This is due to the assumed stability of the crucial bicyclic peroxy radical (BPR), an intermediate that is intrinsic to aromatic oxidation in general. Recently, we showed that the BPR associated with toluene oxidation can be unstable, and its decomposition is pivotal to the subsequent autoxidation mechanism that leads to HOM. [1]

Through investigating the autoxidation mechanisms of xylene in this work, we establish the importance of aromatic derived BPR decomposition to the formation of SOA. We combine theoretical modelling with sub-second HOM measurements using CIMS to develop the Aerosol Dynamics gas- and particle-phase chemistry model for laboratory CHAMber (ADCHAM) code [2] for xylene that is robust at reproducing the SOA mass yields we measure from our chamber experiments. We also show that the underlying autoxidation mechanisms are remarkably similar for many of the atmospherically dominant monocyclic aromatics, which opens the remarkable prospect of significantly improved model predictions of aromatic SOA even in the absence of theoretical and experimental data.

[1] Iyer, S., Kumar, A., Savolainen, A. et al. Molecular rearrangement of bicyclic peroxy radicals is a key route to aerosol from aromatics. Nat. Commun. 14, 4984 (2023). https://doi.org/10.1038/s41467-023-40675-2

[2] Roldin, P., Eriksson, A.C., Nordin, E.Z., Hermansson, E., Mogensen, D., Rusanen, A., Boy, M., Swietlicki, E., Svenningsson, B., Zelenyuk, A. and Pagels, J., 2014. Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas-and particle-phase chemistry kinetic multilayer model ADCHAM. Atmospheric Chemistry and Physics, 14(15), pp.7953-7993.

How to cite: Iyer, S., Kumar, A., Barua, S., Zhao, J., Savolainen, A., Seal, P., Pichelstorfer, L., Roldin, P., Ehn, M., and Rissanen, M.: Towards understanding aromatic SOA by studying the molecular level oxidations mechanisms of xylene isomers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9952, https://doi.org/10.5194/egusphere-egu24-9952, 2024.

Synthetic musk compounds, like cashmeran, are a group of semi-volatile organic compounds commonly used as fragrances in perfumes. In addition to being potential indoor pollutants, they are also regarded as emerging outdoor pollutants, known at volatile chemical products (VCPs). Cashmeran is a bicyclic synthetic musk compound, and a major component of a commercial perfume for men. Here, we aim to better predict the atmospheric fate of cashmeran indoors and outdoors using a Vocus proton transfer time-of-flight mass spectrometer.

Using the Vocus, we show that cashmeran was the dominant musk in a commercial perfume among other musk compounds like galaxolide, astratone, and rosamusk. Next, we measured the rate constant of cashmeran (C₁₄H₂₂O) with ozone for the first time under different experimental conditions to probe its ozonolysis mechanism. In the absence of O₂, we calculated a rate constant of (2.78 ± 0.31) x 10^-19 cm³mol^-1s^-1 at (293 ± 1) K and observed the formation of C₁₄H₂₂O₂ as the key oxidation production. The ozonolysis reaction in the absence of O₂ did not generate SOA. In the presence of O₂, preliminary results show the rate constant to be 5.00 x 10^-18 cm³mol^-1s^-1 at 293 K and the ozonolysis reaction formed SOA with a mass yield of 121 µg m^-3. The rate constant observed in the presence of O₂ indicate the importance of key carbon-radical chemistry and impact of partitioning sinks in understanding the fate of this molecule in the atmosphere. We hypothesize that the slow oxidation of cashmeran with ozone makes loss to partitioning to aerosols a competitive sink in determining its fate.

Furthermore, we investigated how partitioning sinks might be competitive to gas-phase oxidation for the fate of cashmeran from a commercial perfume in an office environment. We show that partitioning to cotton is the major sink, suggesting this molecule can be easily transported outdoors by humans and their clothing.

We further tested this hypothesis during THE CIX urban field campaign in Toronto, Canada in July-August 2023. We detected cashmeran outdoors throughout the campaign up to 10 ppt. As expected from a fragrant VCP, cashmeran peaked during the week only and in the morning. Based on our findings, we conclude that musk compounds, like cashmeran, are long-lived SVOCs capable of impacting urban air quality.

How to cite: Borduas-Dedekind, N., Akande, A., and Depp, C.: The atmospheric fate of cashmeran from musk-smelling volatile chemical products (VCPs) in chamber, indoor, and outdoor environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7733, https://doi.org/10.5194/egusphere-egu24-7733, 2024.

Organosulfates (OS) are a major constituent of atmospheric secondary organic aerosol (SOA). In lack of apparent gas-phase compounds directly contributing to the particulate bound OS, their synthesis has been thought of taking place by acid-catalyzed reactions in the condensed phase, mainly initiated by H₂SO₄. The most well-known sulfur bearing molecules are the isoprene epoxydiol derived organosulfates (Riva et al., 2019). In 2015 Mackenzie et al., showed that under very dry condition SO₃ can react to form sulfuric anhydrides by carboxylic acid + SO₃ reactions (Mackenzie et al., 2015). More recently, several theoretical papers have reported a more general gas-phase source by SO₃ reactions with a multitude of atmospheric acids. The potential importance of this newly found chemistry was highlighted by observations of gas-phase SO₃ in urban Beijing at concentrations similar to H₂SO₄ (Yao et al., 2020), strongly implying that SO₃ reactions are occurring in urban atmospheres.

In the present work we have performed a joint experimental-theoretical characterization of acid + SO₃ reactions utilizing flow reactor setups coupled to nitrate (NO₃^-) chemical ionization mass spectrometry (CIMS) detection combined with supporting quantum chemical computations and master equation simulations. The studied reactions included mono- and dicarboxylic acids, and the strong acids most associated with atmospheric new particle formation events (i.e., H₂SO₄ and HIO₃; Sipilä et al., 2016; Kerminen et al., 2018). Intriguingly, all acids were found to react rapidly with SO₃ even with rate coefficients approaching the collision limit and were found to result in analogous acid sulfuric anhydride products. These sulfuric anhydrides provide a path for OS partitioning from gas to particle (i.e., “backwards” in considering the common particulate-phase synthesis route). Furthermore, the subsequent particulate-phase hydrolysis of the formed organic sulfuric anhydrides is a potential source of the small acids into the nanoparticles that would not be expected to partition significantly otherwise. The formed sulfuric anhydrides, especially the disulfuric acid and iodic acid sulfate, are likely to have similar, if not better, properties at initiating NPF as their parent compounds have.

References:

Kerminen, V.-M. et al., Atmospheric new particle formation and growth: review of field observations, Environ. Res. Lett. 2018, 13, 103003.

Mackenzie, R. et al., Gas Phase Observation and Microwave Spectroscopic Characterization of Formic Sulfuric Anhydride, Science 2015, 349, 58−61.

Riva, M. et al., Increasing Isoprene Epoxydiol-to-Inorganic Sulfate Aerosol Ratio Results in Extensive Conversion of Inorganic Sulfate to Organosulfur Forms: Implications for Aerosol Physicochemical Properties, Environ. Sci. Technol. 2019, 53, 8682-8694.

Sipilä, M. et al., Molecular-scale evidence of aerosol particle formation via sequential addition of HIO3, Nature 2016, 537, 532-534.

Yao, L. et al., Unprecedented ambient sulfur trioxide (SO3) detection: Possible formation mechanism and atmospheric implications, Environ. Sci. Technol. Lett. 2020, 7, 809-818.

How to cite: Rissanen, M., Iyer, S., Barua, S., Besic, E., Seal, P., and Kumar, A.: Reversing the particulate-phase organosulfate chronology: Direct organosulfur compound synthesis in the gas-phase by SO3 + acid reactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8748, https://doi.org/10.5194/egusphere-egu24-8748, 2024.

Many of the quantitative descriptions of secondary organic aerosol (SOA) formation in regional and global models are derived from environmental chamber experiments, an experimental approach commonly used to assess multi-phase product distributions from atmospheric oxidation pathways.  As such, model accuracy for predicting aerosol abundance hinges on our ability to represent atmospheric conditions in chambers.  Here, we develop a new experimental approach that leverages both global modeling and detailed mechanisms to design chamber SOA experiments that capture atmospheric chemical environments for two key branching points in VOC oxidation: atmospheric oxidant balances and atmospheric RO₂ chemistry. Using isoprene as a model system for multi-generation SOA production, we focus first on competition between oxidation by OH and Cl.  Global modeling indicates that multi-oxidant, multi-generation oxidation outcompetes single-oxidant, multi-generation oxidation in this system; we design and perform a series of chamber experiments to measure multi-phase product distributions from multi-oxidant, multi-generation isoprene oxidation.  Second, we develop a framework for quantitatively describing atmospheric RO₂ chemistry and show that no previous experimental approaches to studying SOA formation have accessed the relevant atmospheric RO₂ chemistry.  Leveraging multi-scale modeling, we design and perform a series of chamber experiments to measure isoprene SOA production under a range of atmospheric RO₂ fate distributions.

How to cite: Kenagy, H., Heald, C., Tahsini, N., Goss, M., and Kroll, J.: Integrated model-measurement approaches to chamber SOA studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18908, https://doi.org/10.5194/egusphere-egu24-18908, 2024.

Secondary Organic Aerosol (SOA) production and chemical composition play a crucial role in the urban air pollution. Here, we used observations from two summer campaigns in Beijing in 2017 and 2023 to show that nighttime production of NO_z (NO_y - NO_x) is particularly enhanced in specific conditions and that can play a significant role for SOA the next day. The observations showed nocturnal peaks of NO_z of about 40 ppb, correlated with very high NO and NO₂. We employed the Framework for 0-D Atmospheric Modeling (F0AM) model, based on the Master Chemical Mechanism (MCM), running simulations to investigate the organic nitrates (ONs) speciation, and founding that during the night the alkyl nitrates is the most abundant ONs, produced by oxidation of volatile organic compounds (VOCs) by the nitrate radical (NO₃). Finally, we used the Framework for 0-D Atmospheric Modeling- Washington Aerosol Module (F0AM-WAM) model, which couple the gas phase chemistry with the SIMPOL representation for the particle phase, to correlate the nocturnal ONs peaks, that we suggested to be mainly in gas phase, to the diurnal particle growth events registered in Beijing.

How to cite: Aruffo, E., Wang, J., Jacob, D. J., Ye, J., Ge, X., and Di Carlo, P.: Role played by Organic Nitrates in the Production of Secondary Organic Aerosol in a megacity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16619, https://doi.org/10.5194/egusphere-egu24-16619, 2024.

How to cite: Nelson, C., Andersen, S. T., and Crowley, J. N.: Aircraft measurements of PAN (CH3C(O)OONO2) and PAA (CH3C(O)OOH) in the tropical atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13530, https://doi.org/10.5194/egusphere-egu24-13530, 2024.