Urban volatile organic compounds (VOCs) are key precursors of tropospheric ozone and secondary organic aerosols (SOA), yet their long-term dynamics and health implications remain unclear across Europe. Here, we synthesize two decades of VOC observations (2002-2023) from 21 urban monitoring sites in six countries to assess emission trends, oxidation potentials, and human exposure risks. Consistent declines in total hydrocarbons were observed at most sites, reflecting the effectiveness of emission control policies. Aromatic hydrocarbons such as toluene, xylene, and benzene were the dominant contributors to ozone and SOA formation. Physiologically based toxicokinetic (PBTK) modeling suggests that key VOCs preferentially accumulate in the kidney and liver. The integration of atmospheric monitoring with toxicokinetic modeling provides a multi-scale understanding of how urban VOCs influence both air quality and internal human exposure, offering new insight into effective pollution control strategies.

Tiivistelmä Uudistettu ilmanlaatudirektiivi (EU) 2024/2881 astui voimaan 11.12.2024. Uudistetun direktiivin uudet vaatimukset astuvat voimaan kahden vuoden siirtymäajan puitteissa. Uudet vaatimukset aiheuttavat muutoksia ilmanlaadun vastuisiin, seurantaan, raportointiin ja tarvittaviin toimenpiteisiin. Näitä ovat mm. tiukentuneet raja-arvot ja arviointikynnykset, uusien huolta-aiheuttavien ilmansaasteiden seurantavelvoitteet sekä uusi supermittausasemakonsepti, ilmansuojelun etenemissuunnitelmat sekä kansalaisten tiedottamiseen liittyvät velvollisuudet kuten ilmanlaatuindeksi. Tässä vaikutusten arvioinnissa on tarkoitus selvittää ne keskeiset tekijät, jotka aiheuttavat muutoksia Suomessa ilmanlaadun vastuisiin, seurantaan, raportointiin, tiedottamiseen ja muihin toimenpiteisiin hankesuunnitelman mukaisesti. Tuloksena on uudistetun direktiivin kansallinen vaikutusarviointi, joka sisältää myös kustannusarviot uusista vastuista ja tehtävistä. Lisäksi vaikutusarviointi toimii kansallisena suunnitelmana, miten muutokset toteutetaan sisältäen ehdotukset vastuutahoiksi sekä käytännön toteutussuunnitelman. Arvioinnissa on myös esitetty joitain lisäselvitystarpeita.

Marine ecosystems influence atmospheric chemistry and climate by exchanging volatile organic compounds (VOCs) with the atmosphere, yet the chemical diversity and the environmental controls of the exchanged compounds remain poorly constrained at ecosystem timescales. This gap persists because most marine observations are targeted, short-term, and narrow-suite measurements that seldom deliver chemically broad, continuous fluxes. Here we show that marine VOC exchange is chemically diverse and changes in magnitude and composition on event‑to‑season timescales. Using continuous flux measurements of 48 compounds in the Baltic Sea, we observe a pronounced reorganization of net exchange: early organosulfur emissions diminish as cyanobacterial biomass declines (indicating water-side source limitation), while oxygenated and nitrogen-containing VOCs exhibit mixed behaviors ranging from deposition to episodic emissions (often driven by kinetic factors). Together, these results demonstrate that chemically diverse marine VOC exchange is closely coupled to wind-induced mixing, water‑column structure, and phytoplankton community succession, highlighting the need to resolve these dynamic ecosystem states to predict future atmospheric composition.

A key challenge in semiarid savannas is determining whether ambient isoprene directly traces local biogenic emissions or represents an integrated signal shaped by chemistry and atmospheric dynamics. Here we use hourly measurements of isoprene, methyl vinyl ketone, and methacrolein from August to December 2024 at a savanna site near the Okavango Delta, Botswana, spanning dry to early wet seasons. During the early-wet seasons, daytime isoprene increased with vegetation growth and followed the expected daytime pattern of biogenic emission, suggesting a stronger local contribution. During the dry seasons, isoprene often increased at night, with patterns consistent with stronger atmospheric processing and shallow nighttime boundary-layer influence. Back-trajectory analyses suggested a preferred upwind sector, consistent with possible recent transport. These results suggest that seasonal state affects both isoprene abundance and its representativeness as a proxy for local biogenic emissions in semiarid savannas.

This study presents results from an Intensive Measurement Period (IMP2022) conducted during the European heatwave of July 2022, focusing on ozone, volatile organic compounds (VOCs), and carbonaceous aerosols at 31 sites across Europe. The episode featured persistent high-pressure systems, record-breaking temperatures, widespread ozone exceedances and concurrent atmospheric new particle formation and growth events. Coordinated measurements and chemistry transport modelling were used to examine the spatial variability of ozone, VOC composition, and secondary organic aerosol (SOA) formation under extreme meteorological conditions. Oxygenated VOCs (O-VOCs) constituted the largest fraction of total measured VOC mixing ratios, followed by non-methane hydrocarbons (NMHCs) and aromatics, with contributions from both anthropogenic and biogenic sources. Sensitivity simulations indicate that ozone formation was predominantly NOx-limited across most regions during IMP2022. However, the highest ozone peaks occurred under conditions of elevated NOx in combination with enhanced BVOC emissions. In contrast, SOA formation was slightly enhanced under low-NOx conditions and reduced in elevated NOx. Isoprene, aliphatic NMHCs, and O-VOCs dominated the ozone formation potential, while aromatics and monoterpenes were major contributors to SOA potential. Model simulations indicated that higher NOx concentrations can reduce SOA formation by about 10 %. The campaign also highlighted observational gaps underscoring the need for broader and higher-resolution VOC monitoring across Europe. Overall, further reductions in NOx emissions, alongside targeted control of key anthropogenic VOCs, would benefit air quality under future climate extremes.

Wood construction uses forest biomass effectively and stores carbon. As a biophilic material, wood provides wellbeing benefits; however, its sensory properties, particularly those of Scots pine (Pinus sylvestris), one of the most commonly used wood species in construction, remain under-researched. A study involving 50 participants examined the effects of wood scent and visual stimuli on wellbeing. Participants visited a control room and rooms featuring scent, virtual walls, or both, completing tests and questionnaires. The results indicated that virtual walls combined with wood scent significantly reduced stress and enhanced restoration, with a mean Restoration Outcome Scale (ROS) score 0.47 points higher than the control and 0.30 points higher than with scent alone. There is a 96% and 92% confidence that ROS values are greater with both stimuli. While no significant difference was found between single stimuli, there is a 92% certainty that ROS is higher with virtual walls compared to the control. These findings suggest that wooden virtual environments and wood scent could support cognitive training and emotional regulation. However, further research is needed to explore long-term effects and optimal stimulus levels.

This study presents new Emission Factors (EFs) for regulated and non-regulated pollutants from ferries obtained from a land-based measurement campaign in the harbour of Dunkirk, northern France. Despite Dunkirk being in a sulphur and NOx Emission Control Area (ECA), we show that SO2 remains a reliable tracer of ship emissions in this harbour. A comprehensive suite of gas and particulate phase pollutants was investigated, focusing on 68 Volatile Organic Compounds (VOCs) and 5 components of particles below 1 mu m (PM1) In total, 149 plumes were detected from three similar ferries. Individual EFs were calculated for 84 pollutants, including different navigational phases. Clear identification of the ship plumes led to the robustness of EF estimates, as shown by the low sensitivity to the background correction method. Particle Number (PN) showed a ship specific unimodal distribution around 91 nm. The EF(PN) ranged from 1.04.10(16) to 2.57.10(16) particles kg(fuel)(-1), which is about three times higher than those recently reported in Marseille, southern France. The EFs of the particulate phase components are dominated by Organic Aerosols (OAs) with an interquartile range between 3.79 and 6.82 g kg(fuel)(-1), two to three orders of magnitude higher than nitrates (NO3-) and sulphates (SO2-4 ). The EFs of VOCs are dominated by oxygenated species, such as acetaldehyde (165.6-278.9 mg kg(fuel)(-1)) and methanol (94.56-309 mg kg(fuel)(-1)). The second most emitted group of VOCs are the C5 compounds, with notably cyclopentane (C5H10 center dot H+) (73.2-145.2 mg kg(fuel)(-1)) and the fragment C5H8 center dot H+ (144.2-247 mg kg(fuel)(-1)). Aromatic VOCs, such as benzene (C6H6 center dot H+), toluene (C7H8 center dot H+) and xylenes/ethylbenzene (C8H10 center dot H+), are also detected with individual EFs below 70 mg kg(fuel)(-1). This study also investigated the emissions as a function of the operational phases, suggesting that some VOCs, Black Carbon (BC) and PM1 are more emitted during the arrival than the departure of the ferries. The EFs of the speciated VOCs and PM1 reported here provide a comprehensive database for improving current emission inventories and a better understanding of the role of shipping emissions on air quality degradation, notably along coastal areas.

Long-term nutrient loading and warmer, longer summer temperatures have promoted summer cyanobacteria-dominated phytoplankton blooms in the Baltic Sea, shifting the annual chlorophyll maximum toward peak summer. In turn, organic matter production is increasing, altering the carbon cycle by shifting the bioavailable carbon pool to later in the season and towards microbial heterotrophy. These ecosystem changes may have consequential impacts on the production of trace gases, such as volatile organic compounds (VOC). Enhanced stratification and reduced vertical mixing may further regulate VOC water-air exchange. In the coastal zone, significant changes to macroalgae communities have been observed in association with persistent eutrophication. Shifting coastal dynamics, along with increased warming and, consequently, increased decomposition of organic material, will likely impact VOC production. Therefore, the aim of this study is to evaluate the influence of a summertime phytoplankton bloom on the composition and concentrations of VOCs in seawater, and to examine differences between distinct coastal habitats.Summer sampling was conducted on Utö Island (59º 46'50N, 21º 22'23E; Archipelago Sea), and samples were processed at the Utö Atmospheric and Marine Research Station. Seawater VOCs were collected using the purge and trap method four times across three habitat types along the open coast—open water (250 m off shore; 4.5 m depth), a cove (15 m off shore; 0.5 m depth), and a vegetated beach (on shore; surface). Samples were stored in stainless steel absorbent cartridges and analyzed with Thermal Desorption Gas Chromatography Mass Spectrometry. Phytoplankton community composition and abundance were captured using an Imaging FlowCytobot, complemented by bacterial abundance from flow cytometry and microscopy.Preliminary results indicate clear temporal variability in open water VOC concentrations. Some compounds such as isoprene were persistently detected throughout the summer whereas other compounds, e.g. toluene and dimethyl disulfide, varied across the season in association with changes in phytoplankton and bacterial abundance. Taxa-specific links between VOCs and phytoplankton composition, as well as the potential influence of abiotic drivers, including dissolved organic matter and vertical mixing, is still under investigation. Further analysis indicates that VOC concentrations are highly dependent on coastal habitat type, with composition and concentration of VOCs from the vegetated beach showing approximately 10-fold higher values as well as a more unique VOC blend, suggesting contributions from macroalgae and sediment processes. In contrast, the cove was highly dominated by bromoform, comprising >50% of the measured proportional VOC signal throughout the summer.

Recent studies suggest that terpenes in urban air may have substantial anthropogenic sources, yet distinguishing these from biogenic emissions remains challenging. In this study, we measured terpene concentrations in a street canyon in Helsinki during cold winter months (mean temperature < 0 °C), when biogenic emissions were expected to be minimal. Monoterpenes were observed at mean concentrations of ~160 ng m⁻³, more than an order of magnitude lower than the mixing ratios of aromatic hydrocarbons. Nevertheless, their high reactivity with hydroxyl radicals, nitrate radicals, and ozone led to a disproportionately large contribution to local atmospheric oxidation processes. This pronounced reactivity, combined with their high secondary organic aerosol (SOA) formation potential, indicated the important potential role of anthropogenic terpene emissions even in wintertime SOA formation.

This article presents the results of long-term air quality measurements (2015–2024) from the Helsinki Traffic Supersite, including gaseous compounds (NO, NO2, CO, CO2, O3), particulate matter (PM2.5, PM10, particle number (PN) and size distribution), chemical composition of PM (black carbon (BC), organic aerosol (OA), inorganic species), lung-deposited surface area (LDSA), polycyclic aromatic hydrocarbons, volatile organic compounds (VOC), as well as road surface conditions and meteorology. In addition to the long-term observations, large number of targeted short-term measurement campaigns were conducted to investigate emerging phenomena, to further develop supersite measurements and gain new information about sources impacting air quality.The observed air quality improvements at the Traffic Supersite were driven by declining traffic exhaust concentrations (NOx (-8.0%/yr), BC (-7.1%/yr), PN (-3.7%/yr), and anthropogenic VOCs (-3.1 to -8.9%/yr)). The observed emission factors (g/kgfuel) also decreased for NOx (-7.6%/yr), BC (-7.5%/yr), and PN (-4.1%/yr), reflecting fleet renewal. The observed rate of decrease in PN concentration was lower than that of other parameters, particularly in the smallest size classes (< 30 nm). Organic aerosol analysis showed that traffic hydrocarbon tracers (m/z 57) declined faster (-7.9%/yr) than total OA and oxidized OA (m/z 44), which are linked to secondary formation and long-range transport. Long-term results indicate that compliance with the upcoming EU Air Quality Directive limit values for 2030 is already largely achievable, with the most challenging aspect being the exceedances of the PM10 daily limit due to road dust events. However, achieving the EU Zero Pollution target for 2050 remains challenging, and the WHO guideline values for PM10, PM2.5 and NO2 continue to be exceeded. These unique findings highlight the importance of comprehensive, long-term supersite measurements for understanding pollutant sources and trends, and for supporting urban planning and policy development.

Exhaust gases and particles from ships are a significant and growing contributor to the total emissions from transport. Globally, the sector is a significant contributor to global emissions of NOx and SO2.1,2 Recently, the International Maritime Organisation (IMO) has reduced the sulphur content of marine fuels globally through Annex VI of MARPOL, and sulphur emissions are further restricted in specific Sulphur Emission Control Areas (SECA), such as the English Channel between France and the UK. Similarly, NOx emission limits have been set for ships built after 2016 in NOx Emission Control Areas (NECA).However, other pollutants such as Volatile Organic Compounds (VOCs) or Particulate Matter (PM), are not regulated in relation to ship emissions. Here, we present new emission factors (EFs) for regulated and non-regulated pollutants from ship emissions derived from a land-based measurement campaign in the port of Dunkirk, France in the framework of the PIRATE and SHIPAIR projects. A comprehensive suite of gas-phase and particulate-phase pollutants was investigated with a focus on VOCs, based on PTR-MS measurements, and PM1 composition, based on AMS measurements. About 150 plumes were detected from three similar ferries, and EFs were calculated for 84 pollutants.Despite being located in an Emission Control Area (ECA) for SOx and NOx, we show that SO2 remains a reliable tracer of ship emissions for land-based measurements in the port area. A sensitivity test of the EF with respect to background considerations was performed, showing significant discrepancies depending on the method of background calculation. This underlines the importance of explicit background considerations in EF calculations.The EF of the particulate phase is dominated by the organic fraction (OA), between 0.05 and 15.88 g/kg fuel, two to three orders of magnitude higher than nitrate and sulphate. Particle Number (PN) EFs vary between 1.08·1014 and 1.60·1017 part./kgfuel, with a unimodal mode centred at 90 nm. The VOC EFs are dominated by oxygenated species, such as acetaldehyde (30.7 - 404.8 mg/kg fuel). The second most emitted group of VOCs are C5 cyclic compounds, of which cyclopentane has the highest EF (12.8 - 439.6 mg/kg fuel). Aromatic VOCs, such as benzene, toluene and xylenes, are also detected, with EFs below 80 mg/kg fuel. We also present the emissions as a function of the navigation phases, suggesting that certain pollutants are emitted more during the arrival of the ferries than during their departure. In particular, the speciated VOC EFs are expected to improve current emission inventories.References :(1) Aakko-Saksa, P. T. et al. Reduction in greenhouse gas and other emissions from ship engines: Current trends and future options. Progress in Energy and Combustion Science 94, 101055 (2023). (2) Lehtoranta, K. et al. Particulate Mass and Nonvolatile Particle Number Emissions from Marine Engines Using Low-Sulfur Fuels, Natural Gas, or Scrubbers. Environmental Science and Technology 53, 3315–3322 (2019).

Long-term observations of coastal ecosystems and atmosphere are crucial for addressing global challenges like air pollution, water, energy, and food supply. Coastal environments are ecological hotspots acting as greenhouse gas sinks/sources, emitting volatile organic compounds (VOCs) and trace gases, and impacting marine aerosol formation. The Tv & auml;rminne Zoological Station (TZS) in the northern Baltic Sea has a long history of marine biology observations. In 2022, a comprehensive atmospheric observatory was established at TZS, leading to the creation of coastal-SMEAR (Station for Measuring Earth surface-Atmosphere Relations). Equipped with advanced instrumentation, the key aim of this station is to understand potential feedbacks between coastal ecosystems and the atmosphere. Initial results indicate that the sea-air exchange of aerosol precursor gases, VOCs and CO2 at the coast are highly dynamic, influenced by meteorological and biological conditions. Establishing SMEAR stations in different coastal environments would greatly help to understand coastal ecosystem-atmosphere feedbacks.

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, 2016Praplan, 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.

Diterpenes, found in trees, have been overlooked in atmospheric chemistry due to their low volatility and presumed negligible emissions. However, advances in sampling and analytical methods now allow for their detection in the gas phase. Here we quantify diterpene emission factors and evaluate their role in secondary organic aerosol formation. By incorporating all available emission data and laboratory-derived aerosol yields into the MONARCH chemistry transport model, we assessed their atmospheric contribution. Chamber experiments revealed kaurene yields of 1.8-17%, indicating efficient gas-to-particle conversion. Global emissions were estimated at 11.5 (0.1-94.3) Tg yr-(1), contributing 0.63 (0.005-5.19) Tg yr-(1) to secondary organic aerosol production and a burden of 0.008 (0.00007-0.07) Tg. This corresponds to 13%, 6.4%, and 19% of the aerosol burden from isoprene, monoterpenes, and sesquiterpenes, respectively. These results demonstrate that diterpenes are a previously underestimated, but potentially important, source of secondary organic aerosol, with implications for biosphere-atmosphere interactions.

To study the drivers of volatile organic compound (VOC) emissions from boreal forest soil emissions, a study was conducted at two long-term and well-documented experiments in Finland. The first experiment, located in Karkkila (60.577°N, 24.261°E), is a spruce dominated stand with a nitrogen (N) fertilization experiment. The second experiment is in Taivalkoski (65.316°N, 28.161°E), where a tree species experiment is taking place with individual plots on which either silver birch, Scots pine, or Norway spruce were grown on originally similar soil.Between May and October 2023, we collected soil VOC emissions on multi-bed adsorbent tubes at three locations in each plot (control and N-fertilized in Karkkila, and different tree species in Taivalkoski) about once a month, using an enclosure put on metallic frames placed at each sampling location at least one month before the first sampling. The collected emission samples were analysed with a thermal desorption gas chromatograph coupled to mass spectrometry (TD-GC-MS). The conditions both inside and outside the enclosure were recorded during sampling. Furthermore, the soil moisture was measured, and vegetation was visually assessed after each sampling. In addition, 15 to 20 soil cores were taken by a soil auger around 1-2m of each VOC sampling location during the early growing season, and the organic layer separated. Organic layer samples were combined to make one composite sample for each sampling location. Pretreatments and analysis were performed as described in Soronen et al. (2024) to derive soil parameters, including microbial properties. We also used a microdialysis sampling technique to determine induced diffusive fluxes of plant-available N compounds in the organic layer (Soronen et al., 2024). Fluxes were measured twice during the growing season at each site (early and late season).For a given plot, emissions collected on the same day show similar composition with varying quantities. However, seasonal variations influenced the emissions’ composition, reflecting various direct and indirect underlying processes. Monoterpenes usually dominated the emissions, but chloroform was also emitted, especially from the N-fertilized plot. The relationships between stand properties, soil properties, environmental conditions, and VOC emissions were explored using multiple linear regression. We found that individual compounds are affected differently, emphasizing the importance of speciation. In general, the dominant tree species, moss cover, and shrub cover appear to be the vegetation factors most influencing VOC emissions. From soil properties, increasing dissolved organic carbon, organic matter, and the microbial biomass C-to-N ratio increased BVOC emissions.Rising global temperatures lead to increased biomass in boreal areas (including litter and organic soil matter), an extended growing season, and heat stress. These alterations can affect vegetation, soil microbes, and forest floor plants, potentially causing changes in VOC emissions. The analysis presented here could be used in models of biogenic VOC emissions from boreal forest soils to investigate future scenarios.Reference:Soronen, P., Henttonen, H.M. and Smolander, A. (2024). Grey alder at the regeneration stage: Long-term effects on soil nitrogen and carbon pools and Norway spruce growth. Forest Ecology and Management, 554, 121686. doi:10.1016/j.foreco.2023.121686.

Biogenic volatile organic compounds (BVOCs), primarily emitted into the atmosphere by terrestrial vegetation through biochemical processes, have key ecological functions in protecting vegetation from biotic or abiotic stresses. However, accurately quantifying and predicting changes in BVOC emissions in response to long-term environmental changes large spatial scales remain challenging. The appropriate tools for observing the BVOC emissions at large scales are still missing. Remote sensing of optical signals is a promising solution to fill spatial knowledge gap. We hypothesize that the carotenoid-related vegetation index, such photochemical reflectance index (PRI), is a promising method to investigate BVOCs emitted by plants based on their functional links with carotenoids and photosynthetic activity. We conducted a leaf-level experiment in greenhouse during the summer of 2022 to investigate how the relationships between PRI and BVOC emissions change in response to drought or heat stresses in Scots pine and English oak saplings during the peak of growing season. We aim to address the following questions: (1) What factors control the relationships between PRI and BVOC emissions in response to mild/extreme drought or heat; (2) Will these controlling factors differ between vegetation species or BVOC emission types (e.g., isoprene and monoterpenes)? (3) Can PRI or other carotenoid-related vegetation indices capture the changes of BVOC emissions in response to drought or heat stresses? We will present our preliminary results. The expected outcomes will give new insight into leaf-level mechanistic links between PRI and BVOC emissions for plants in response to climate drought or warming.

Many cities attempt to mitigate poor air quality by increasing tree canopy cover. Trees can indeed capture pollutants and reduce their dispersion, but they can also negatively impact urban air quality. For example, trees emit biogenic volatile organic compounds (BVOCs) that participate in both ozone (O3) and secondary organic aerosol (SOA) formation, yet these emissions have been little studied in urban contexts. We sampled BVOCs from the leaves of mature urban trees using lightweight enclosures and adsorbent tubes in two cities: Montreal, Canada and Helsinki, Finland. In both cities, we targeted five common broadleaved species in parks and streets, comparing their standardised BVOC emission potentials to nonurban BVOC emission potential estimates from emission databases. We also calculated the potential O3 and SOA formation by the study species at the leaf scale and upscaled to the neighbourhood. We found that the measured BVOC emission potentials generally deviated little from the emission database estimates, supporting the use of database estimates for urban trees. However, tree-to-tree variation in the BVOC emission potentials was large, with slight differences between park and street trees. Compared to park trees, street tree emissions were higher in Montreal (specifically isoprene and sesquiterpenoids) and lower in Helsinki (specifically green leaf volatiles). Finally, we found that O3 formation from our study species' BVOC emissions was dominated by isoprene, while SOA formation was also affected by lower monoterpenoid and sesquiterpenoid emissions. These findings highlight the importance of species selection and management strategies that protect trees from BVOC-inducing stresses.

BTEX (benzene, toluene, ethylbenzene, and m-xylene,p-xylene, and o-xylene) are significant urban air pollutants. This study examines BTEX variability across 7 European countries using data from 22 monitoring sites in different urban settings (urban background, traffic, industry, and suburban background). Results indicate that the relative abundance of BTEX in urban areas follows the order toluene > benzene > m,p-xylene > o-xylene > ethylbenzene, with median mixing ratios of 266 ± 152, 163 ± 74, 129 ± 88, 53 ± 35, and 45 ± 27 ppt during the years 2017–2022, respectively. Seasonal trends show benzene had similar median concentrations across urban background, traffic, and industrial sites, indicating mixed sources. Toluene levels were highest in traffic and industrial areas, highlighting road traffic and industrial emissions. Ethylbenzene and xylenes showed equivalent levels in traffic and industrial areas but were lower in urban backgrounds. Peak BTEX levels occurred during morning and evening rush hours, linked to traffic, heating, and atmospheric stagnation. B/T ratios ranged from 0.29 ± 0.11 to 1.35 ± 0.95, and X/E ratios ranged from 1.75 ± 0.91 to 3.68 ± 0.30, indicating primary pollution from local traffic, followed by solvents, coatings, and biomass burning. Lifetime cancer risk from BTEX exposure was below the definite risk threshold (10−4) but above the permissible risk level (10−6), suggesting moderate risk from benzene and ethylbenzene, particularly in traffic and industrial areas. Additionally, the health index of BTEX at monitoring sites was generally lower than the threshold limit value, suggesting a low non-carcinogenic risk overall. This study offers essential insights into BTEX pollution in urban European environments.

Physical and chemical properties of particulate matter and concentrations of trace gases were measured at an urban site in Helsinki, Finland, for 5 weeks to investigate the effect of wintertime conditions on pollutants. The measurement took place in a street canyon (traffic supersite) in January–February 2022. In addition, measurements were conducted in an urban background station (UB supersite, SMEAR III, located approx. 0.9 km from the traffic supersite). Measurements were also made using the mobile laboratory. The measurements were made driving the adjacent side streets and the street along the traffic supersite. Source apportionment was performed for the soot particle aerosol mass spectrometer measurements to identify organic factors connected to different particulate sources. Particle number concentration time series and the pollution detection algorithm were used to compare local pollution level differences between the sites. During the campaign three different pollution events were observed with increased pollution concentrations. The increased concentrations during these episodes were due to both trapping of local pollutants near the boundary layer and the long-range and regional transport of pollutants to the Helsinki metropolitan area. Local road vehicle emissions increased the particle number concentrations, especially sub-10 nm particles, and long-range-transported and regionally transported aged particles increased the PM mass and particle size.