Biomass burning (BB) is the second largest global source of organic aerosol (OA), with its impact on climate and air quality expected to rise with global warming. Aircraft measurements of BB plumes show a rapid increase in the OA oxidation state, which could not be reproduced in simulation chambers based on gas-phase oxidation. Here, we investigate isolation key aging processes of BB emissions in controlled chamber experiments, including the effects of ultraviolet-A irradiation, OH-driven secondary OA formation, heterogeneous OH oxidation or ozonolysis, and evaporation. We find that ultraviolet-A irradiation can drive rapid intraparticle OA aging within hours, proceeding an order of magnitude faster than gas-phase oxidation. Other mechanisms were even slower in producing oxygenated OA (OOA). Based on our experiments, we estimate that this process proceeds with a quantum yield of ∼0.4%, meaning that four in every thousand photons absorbed by organic chromophores in BBOA generate radicals in the particle phase that rapidly oxidize the particulate organics. We further analyzed aircraft measurements of wildfire and prescribed burn plumes, showing that photoinduced processes can account for much of the rapid OOA formation. We estimate that, in BB-influenced regions, over half of OOA may originate from photo-oxidized primary OA within the first day. Our findings challenge the prevailing paradigm that gas-phase oxidation dominates BBOA aging and highlight a previously underappreciated, but dominant role of intraparticle photochemistry.

Volatile methyl siloxanes (VMS) are anthropogenic compounds widely used in personal care products and industrial applications and are frequently detected at elevated concentrations in urban air. However, their sources in urban areas remain poorly constrained. Here, we use chassis dynamometer experiments to quantify gas-phase VMS emissions from a range of on-road vehicles, including light-duty gasoline and diesel vehicles. Hexamethylcyclotrisiloxane (D-3) dominated the emitted VMS, over octamethylcyclotetrasiloxane (D-4), and decamethylcyclopentasiloxane (D-5). VMS emissions increased with driving speed and were substantially higher from gasoline than from diesel vehicles. Comparison with tunnel measurements showing elevated ambient VMS concentrations supports a significant contribution from traffic-related sources, including tailpipe and potentially nontailpipe emissions. These results identify vehicular emissions as a previously underrecognized source of VMS near highways, and provide new constraints for their atmospheric budget and source apportionment.

Biomass burning organic aerosol (BBOA) is a significant source of brown carbon (BrC), a class of light-absorbing organic compounds that influence the climate and atmospheric oxidation chemistry. Certain BrC chromophores act as photosensitizers by producing reactive oxidants such as singlet oxygen (1O2 *) and triplet excited states (3C*) upon solar irradiation, but we still cannot predict which functional groups drive the production of these excited-state oxidants. We hypothesized that since the major sink for O 2 * 1 is solvent deactivation, water-based extractions of chromophores may (1) underestimate O 2 * 1 production in BBOA, as well as (2) overlook water-insoluble chromophores potentially important in hydrophobic aerosol phases. To better represent the multiphase nature of atmospheric aerosols in this work, we employed a cosolvent extraction using acetonitrile and water to extract the hydrophobic fraction of BrC chromophores. Primary organic aerosol (POA) filters from the combustion of beechwood, cow dung, straw, and plastic were collected during the BAMBE campaign and subsequently analyzed using a two-probe photochemical method with furfuryl alcohol and syringol as probes to quantify O 2 * 1 and 3C* steady-state concentrations and quantum yields, respectively, under UVA irradiation. The acetonitrile-water mixture enhanced chromophore recovery and modulated the quenching of the excited state of O 2 * 1 back to O2, leading to up to a 6-fold increase in O 2 * 1 concentrations. Fuel type significantly influenced oxidant yields. Beechwood and plastic extracts showed the highest O 2 * 1 and 3C* production, up to 4.9 +/- 0.1% for O 2 * 1 and 4.2 +/- 0.2% for 3C*, respectively. Complementary FIGAERO-CIMS analysis revealed compositional differences between fuels and combustion conditions, suggesting that nitrogen-containing species drove the variability in sensitization efficiency. Our findings underscore the importance of solvent selection and fuel source in assessing BrC photochemical activity and offer new insights into the oxidative potential of BBOA in atmospheric multiphase environments.

Volatile methyl siloxanes (VMS) are anthropogenic compounds widely used in personal care products and industrial applications and are frequently detected at elevated concentrations in urban air. However, their sources in urban areas remain poorly constrained. Here, we use chassis dynamometer experiments to quantify gas-phase VMS emissions from a range of on-road vehicles, including light-duty gasoline and diesel vehicles. Hexamethylcyclotrisiloxane (D3) dominated the emitted VMS, over octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5). VMS emissions increased with driving speed and were substantially higher from gasoline than from diesel vehicles. Comparison with tunnel measurements showing elevated ambient VMS concentrations supports a significant contribution from traffic-related sources, including tailpipe and potentially nontailpipe emissions. These results identify vehicular emissions as a previously underrecognized source of VMS near highways, and provide new constraints for their atmospheric budget and source apportionment.

Atmospheric simulation chambers are one of the best available tools to study atmospheric processes, as they enable experiments under conditions that are both reproducible and well-controlled. 16 unique simulation chamber facilities are part of the distributed pan-European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Their research focuses on fundamental gas-phase reaction kinetics, complex reaction mechanisms, aerosol formation and cloud chemistry, as well as other aspects of atmospheric processes. They use both simplified and complex air mixtures in their research. Results of chamber experiments enable the discovery of unknown chemical mechanisms and the determination of physicochemical parameters of atmospheric constituents. Simulation chambers are ideal for testing instruments and quality assurance of their data. The variability of their research capability is reflected in differences in the size (ranging from approximately 1-270 m3), the wall material, and the type of instrumentation used to measure physical parameters, gas-phase species, physicochemical properties of aerosol particles as well as cloud droplets and ice crystals. Most chambers in ACTRIS are indoors and use artificial light sources to initiate photochemical reactions while some chambers are located outside so that natural sunlight can be used. During experiments, steady state conditions may be achieved, the evolution of initial conditions may be observed, or expansion and mixing techniques may induce cloud formation. In this paper, the ACTRIS simulation chambers are described along with the quality control measures for carrying out experiments and reporting data. An overview of how users from the research community and industry can gain access to the ACTRIS simulation chambers and associated data centre is presented. Recent developments in the application of ACTRIS simulation chambers for answering current and future atmospheric research questions are discussed.

Secondary organic aerosol (SOA) is a significant contributor to the global burden of fine particulate matter, which impacts both climate and health. α-Pinene is a widely-studied volatile organic compound (VOC) with high global emissions and SOA-forming potential. However, the vast majority of SOA forms on preexisting particles whose composition leads to different molecular species and physical properties. Understanding the viscosity of SOA-containing particles is critical to predicting their atmospheric behavior, as it influences heterogeneous chemistry, particle growth, and particle aging. The viscosity of SOA can range over many orders of magnitude from liquid (<102 Pa s) to viscous to glassy (>1012 Pa s). Nanothermal analysis (NanoTA) measures single particle melting temperatures (T m) for submicron particles, which can be converted to glass transition temperatures (T g), viscosities, and, ultimately, mixing time scales. In this study, we directly measured the T m of α-pinene SOA formed with no seeds, ammonium sulfate seeds, and Fe-containing ammonium sulfate seeds, both before and after UV exposure. We compare these to modeled viscosities based on chemical composition measurements of the bulk aerosol. The median viscosity of measured particles was 1-3 orders of magnitude more viscous than predicted by existing models for all conditions except those of freshly-emitted, unseeded SOA. After UV exposure, the T m values for all seed conditions converged, indicating that aged SOA viscosity was less dependent on the initial seed. These results indicate the importance of pre-existing seed particles for initial SOA viscosity and that this viscosity evolves during a particle's atmospheric lifetime.

INTRODUCTION:Enhancing paediatric asthma diagnosis is crucial. Molecular analysis of exhaled breath is a rapidly evolving field aimed at harnessing established and innovative technologies for clinical applications. This study evaluates the feasibility of using online proton-transfer-reaction mass spectrometry (PTR-MS) to identify distinctive breath signatures in children with allergic asthma. METHODS:Exhaled breath samples of 81 children (41 with allergic asthma and 40 healthy controls) were analysed using the Vocus CI-TOF mass spectrometer (Tofwerk AG, Switzerland), with mass spectra acquired in H3O+ and NH4 + ionisation modes. Significant mass-to-charge (m/z) features were extracted using the Wilcoxon rank-sum test. Molecular identification was conducted using two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-Q-TOF). RESULTS:Statistical analysis revealed 89 significant m/z features associated with paediatric allergic asthma, 66 in H3O+ mode and 23 in NH4 + mode. Supervised machine learning achieved an average accuracy of 74.7% in distinguishing between the groups. GCxGC-QTOF analysis identified a subset of significant features, including four previously reported asthma predictors in breath analysis studies. 16 novel asthma predictor candidates were additionally detected, including 7 likely endogenous, 4 unknowns and 3 exogenous. The main group of breath metabolites was structurally related fatty acids, methyl esters and aldehydes, including four known biomarkers of lipid peroxidation. CONCLUSION:Our findings demonstrate the suitability of PTR-MS for real-time breath analysis in paediatric populations. Moreover, the identification of distinct breath signatures exclusive to allergic asthma in children suggests the potential of leveraging such technology for non-invasive diagnostic applications.

Aerosols play a critical role in the Arctic's radiative balance, influencing solar radiation and cloud formation. Limited observations in the central Arctic leave gaps in understanding aerosol dynamics year-round, affecting model predictions of climate-relevant aerosol properties. Here, we present the first annual high-time-resolution observations of submicron aerosol chemical composition in the central Arctic during the Arctic Ocean 2018 (AO2018) and the 2019–2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expeditions. Seasonal variations in the aerosol mass concentrations and chemical composition in the central Arctic were found to be driven by typical Arctic seasonal regimes and resemble those of pan-Arctic land-based stations. Organic aerosols dominated the pristine summer, while anthropogenic sulfate prevailed in autumn and spring under haze conditions. Ammonium, which impacts aerosol acidity, was consistently less abundant, relative to sulfate, in the central Arctic compared to lower latitudes of the Arctic. Cyclonic (storm) activity was found to have a significant influence on aerosol variability by enhancing emissions from local sources and the transport of remote aerosol. Local wind-generated particles contributed up to 80 % (20 %) of the cloud condensation nuclei population in autumn (spring). While the analysis presented herein provides the current central Arctic aerosol baseline, which will serve to improve climate model predictions in the region, it also underscores the importance of integrating short-timescale processes, such as seasonal wind-driven aerosol sources from blowing snow and open leads/ocean in model simulations. This is particularly important, given the decline in mid-latitude anthropogenic emissions and the increase in local ones.

Isoprene (C5H8) is the non-methane hydrocarbon with the highest emissions to the atmosphere. It is mainly produced by vegetation, especially broad-leaved trees, and efficiently transported to the upper troposphere in deep convective clouds, where it is mixed with lightning NOx. Isoprene oxidation products drive rapid formation and growth of new particles in the tropical upper troposphere. However, isoprene oxidation pathways at low temperatures are not well understood. Here, in experiments at the CERN CLOUD chamber at 223 K and 243 K, we find that isoprene oxygenated organic molecules (IP-OOM) all involve two successive OH ∙ oxidations. However, depending on the ambient concentrations of the termination radicals ( HO 2 ∙ , NO ∙ , and NO 2 ∙ ), vastly-different IP-OOM emerge, comprising compounds with zero, one or two nitrogen atoms. Our findings indicate high IP-OOM production rates for the tropical upper troposphere, mainly resulting in nitrate IP-OOM but with an increasing non-nitrate fraction around midday, in close agreement with aircraft observations.

We present a "diagonal" Volatility Basis Set (dVBS) comparing gas-phase concentrations of oxygenated organic molecules (OOM) to their condensed-phase mass fractions. This permits closure of vapor concentrations with particle composition constrained by particle growth rates, allowing the contributions of quasi non-volatile condensation, equilibrium partitioning, and reactive uptake to be separated. The dVBS accommodates both equilibrium and dynamical (growth) conditions. Growth implies an association between gas and particle concentrations governed by a "condensation line" that is set by the particle growth rate, which fixes the total (excess) concentration of condensible vapors. The condensation line defines an infeasible region of high particle mass fraction and low gas concentration; under steady-state growth conditions, compounds cannot appear in this infeasible region without being formed by condensed-phase chemistry. We test the dVBS with observations from the CLOUD experiment at CERN using data from a FIGAERO I- Chemical Ionization Mass Spectrometer measuring vapors directly and particle composition via temperature programmed desorption from a filter. A dVBS analysis finds that data from an α-pinene + O3 run at 243 K are consistent with volatility driven condensation forming the large majority of particle mass, with no compounds clearly within the infeasible region.

Atmospheric fine particulate matter (PM2.5) has been acknowledged to exert adverse health effects through reactive oxygen species (ROS) initiated oxidative stress. Oxidative potential (OP) is a chemical parameter that reflects the abilities of PM to generate ROS and deplete antioxidants as well. Dithiothreitol (DTT) method was used in this study to measure the OP activity (described as OPDTT). Some redox metals have been demonstrated to possess strong OPDTT activities. However, it is challenging to estimate the contribution of each metal in PM2.5 to OPDTT by chemical method. In this study, the quantitative contribution and ranking of 22 kinds of metals/metalloids to OPDTT were proposed by means of machine leaning models based on hundreds of Beijing PM2.5 samples. Among several combined models, the combined multiple linear regression (modified version) and weighted least square model emerged as the most effective. It was revealed that not only well-known metals such as Mn and Cu were important, but also some less-recognized metals like Tl made significant contributions. The modeled results presented in this paper encompass the contributions of most metals to OPDTT and are conducive to a comprehensive understanding of the health effects of PM2.5.

Secondary organic aerosol (SOA) comprises most of the submicron atmospheric particle mass, and often becomes internally mixed with other particles. When SOA mixes with transition metal (e.g., iron) containing particles, metal-organic complexes can form, enabling photochemical reactions that change aerosol physicochemical properties. We studied the photochemistry of α-pinene SOA formed on iron-containing ammonium sulfate seed particles at varying relative humidities (RH). Chemical composition and photochemical reduction of particles were analyzed by X-ray spectromicroscopy and infrared spectroscopy. SOA formed at low vs. high RH had different chemical functionality, including abundant carboxylic acids and alcohols. Following photolysis, carboxylic acids and unsubstituted alkanes decreased, and alcohols increased, consistent with decarboxylation reactions. Iron in SOA formed at high RH was readily photochemically reduced, but iron in SOA formed at low RH was not. Overall, RH conditions at SOA formation affect not only chemical composition but also iron-complex formation and hence photochemical processing of aerosols.

Solid fuel (SF) combustions, including coal and biomass, are important sources of pollutants in the particle and gas phase and therefore have significant implications for air quality, climate, and human health. In this study, we systematically examined gas-phase emissions, using the Vocus proton-transfer-reaction time-of-flight (PTR-TOF) mass spectrometer, from a variety of solid fuels, including beech logs, spruce/pine logs, spruce/pine branches and needles, straw, cow dung, and coal. The average emission factors (EFs) for organic vapors ranged from 4.8 to 74.2 g kg−1, depending on the combustion phases and solid fuel types. Despite slight differences in modified combustion efficiency (MCE) for some experiments, increasing EFs for organic vapors were observed with lower MCE. The relative contribution of different classes showed large similarities between the combustion phases in beech logs stove burning, relative to the large change in EFs observed. The CxHyOz family is the most abundant group of the organic vapor emitted from all SF combustion. However, among these SF combustions, a greater contribution of nitrogen-containing species and CxHy families (related to polycyclic aromatic hydrocarbons) is observed in the organic vapors from cow dung burning and coal burning, respectively. Intermediate-volatility organic compounds (IVOCs) constituted a significant fraction of emissions in solid fuel combustion, ranging from 12.6 % to 39.3 %. This was particularly notable in the combustion of spruce/pine branches and needles (39.3 %) and coal (31.1 %). Using the Mann–Whitney U test on the studied fuels, we identified specific potential new markers for these fuels based on the Vocus measurements. The product from pyrolysis of coniferyl-type lignin and the extract of cedar pine needle were identified as markers in the open burning of spruce/pine branches and needles (e.g., C10H14O2, C11H14O2, C10H10O2). The product (C9H12O) from the pyrolysis of beech lignin was identified as the potential new marker for beech log stove burning. Many series of nitrogen-containing homologues (e.g., C10H11–21NO, C12H11–21N, C11H11–23NO, and C15H15–31N) and nitrogen-containing species (e.g., acetonitrile, acrylonitrile, propanenitrile, methylpentanenitrile) were specifically identified in cow dung burning emissions. Polycyclic aromatic hydrocarbons (PAHs) with 9–12 carbons were identified with significantly higher abundance from coal burning compared to emissions from other studied fuels. The composition of these organic vapors reflects the burned solid fuel types and can help constrain emissions of solid fuel burning in regional models.

Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the 'Cosmics Leaving Outdoor Droplets' chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products' saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.

While photochemical aging is known to alter secondary organic aerosol (SOA) properties, this process remains poorly constrained for anthropogenic SOA. This study investigates the photodegradation of SOA produced from the hydroxyl radical-initiated oxidation of naphthalene under low- and high-NOx conditions. We used state-of-the-art mass spectrometry (MS) techniques, including extractive electrospray ionization and chemical ionization MS, for the in-depth molecular characterization of gas and particulate phases. SOA were exposed to simulated irradiation at different stages, i.e., during formation and growth. We found a rapid (i.e. >30 min) photodegradation of high-molecular-weight compounds in the particle-phase. Notably, species with 20 carbon atoms (C20) decreased by 2/3 in the low-NOx experiment which was associated with particle mass loss (∼12%). Concurrently, the formation of oligomers with shorter carbon skeletons in the particle-phase was identified along with the release of volatile products such as formic acid and formaldehyde in the gas-phase. These reactions are linked to photolabile functional groups within the naphthalene-derived SOA products, which increases their likelihood of being degraded under UV light. Overall, photodegradation caused a notable change in the molecular composition altering the physical properties (e.g., volatility) of naphthalene-derived SOA.

Secondary organic aerosols (SOA) have significant effects on visibility1, human health2, and climate3. They are formed from the oxidation of volatile organic compounds (VOCs) in the atmosphere, leading to less volatile oxidation products that can subsequently partition into, or react with existing, aerosol particles.4-5 Biomass burning (BB) is estimated to be the second-largest source of VOCs and the largest source of fine OA globally.6 Extreme fires have been estimated to increase by 30% by 2050, which will greatly increase the concentration of BB VOCs and OA in the atmosphere. While photochemistry and humidity are known to influence SOA formation and aging,7–10 their impacts on BB-SOA remain poorly constrained and should be addressed to better capture the evolution of BB-SOA in the atmosphere.In this work, an oxygenated aromatic BB-marker, i.e., o-cresol (C7H8O), and two types of fuels (South African grass and chaparral from California) were used to study the chemical processes leading to the formation and aging of BB-SOA. The experiments were conducted in simulation chambers at PSI and LISA, respectively. Various oxidants (OH, O3, NO3) and humidity levels were used for these experiments, to explore gas- and particle-oxidation processes. A fast-switching chemical-ionization Orbitrap mass spectrometer, and a Vocus proton-transfer-reaction mass spectrometer were used to characterize gaseous species, while BB-SOA were characterized using an extractive electrospray ionization mass spectrometer, and a newly developed Vocus wall-less aerosol load - evaporator (WALL-E) AIM mass spectrometer. 1 Finlayson-Pitts, B. J. et al. Chemistry of the upper and lower atmosphere: theory, experiments, and applications; Academic Press: San Diego, 2000.2 Nel, A. Science 2005, 308, 804–805.3 Boucher, O. et al. IPCC Report 2013, 571–657.4 Ziemann, P. J. et al. Chem. Soc. Rev. 2012, 41, 6582.5 Srivastava, D. et al. NPJ Clim. Atmos. Sci. 2022, 5, 22.6Akagi, S. K. et al. Atmos. Chem. Phys. 2011, 11, 4039–4072.7 McNeill, V. F. Environ. Sci. & Technol. 2015, 49, 1237–1244.8 Xu, W. et al. Environ. Sci. & Technol. 2017, 51, 762–7709 Kuang, Y. et al. Environ. Sci. & Technol. 2020, 54, 3849–3860.10 Wang, J. et al. Proc. Natl. Acad. Sci. (PNAS), 2021, 118.

Observational data collected in December 2014 at the base camp of Mount Everest, Nepal, indicated frequent new particle formation events of pure biogenic origin. Those events were speculated to be controlled by the along-valley winds forming in the valley connecting the Indo-Gangetic plain to the observational site, the Nepal Climate Observatory-Pyramid. The valley winds funnel highly oxygenated organic molecules of biogenic origin to higher elevations where they nucleate. The mechanism was referred to as "The Himalayan aerosol factory". Its geographical extent and climate implications are currently unknown. In view of this, we conducted numerical chemical model simulations to corroborate the presence of the mechanism, and to quantify its geographical extent. Our numerical simulations confirmed that biogenic emissions located in the valleys can be converted into ultra-low volatility organic compounds, transported to the observational site by the along-valley winds, and therein nucleate. The overall time scale of the process, from the release of biogenic emissions to the conversion to ultra-low volatile organic compounds to the arrival time at the observational site, was found to be around 4 hours, consistent with the predicted along-valley winds intensity and the geographical distribution of biogenic emissions. A first estimation of the maximum injection height of biogenic particles, and highly oxygenated organic molecules, indicated the presence of efficient nucleating gases and biogenic particles at an elevation as high as 5000-6000 m a.s.l. These results suggest that the Himalayan chain, under specific weather conditions, is a main contributor to the biogenic aerosol loads in the free troposphere. Considering these findings, field campaigns, especially at the entrance of the valley's floors, and research consortia supporting atmospheric research in Asian mountain regions, are highly encouraged.

It is important to study aerosols and their origins, as they pose various negative health and environmental impacts. In this study, we combined year-long datasets from 15 different countries with Trajectory Statistical Methods (TSMs) for the first time at this comprehensive scale. We found possible source regions and seasonal variations of various particulate matter (PM) components in Europe, including total organic aerosol (OA), biomass burning OA (BBOA), oxygenated OA (OOA), ammonium (NH4), nitrate (NO3), and sulphate (SO4). We found that for all of the studied components, Eastern Europe was among the highest contributors. For NO3, other important source regions were Northern France and the Benelux, while for SO4 there were significant contributions from the Mediterranean region. We also compared our measurement-based model with simulated concentrations of an atmospheric chemistry transport model (CAMx). We observed a satisfactory agreement in regions where we had sufficient coverage with air pollution monitoring stations. The main deviations for OA were found around the Po Valley, where CAMx consistently estimated higher concentrations, while the TSM analysis did not highlight it as a hotspot because long-term monitoring datasets in this region are lacking. CAMx also underestimated the concentrations around Poland, mainly from residential burning. Our results provide opportunities to refine European emission inventories and deliver valuable information on long-range transported air pollutants. This work suggests that policies mitigating air pollution in Eastern Europe and the Benelux could help improve overall air quality in entire Europe more efficiently.

Amid escalating concerns regarding climate change and air pollution, the intricate interplay between climate dynamics and air microbiomes remains inadequately understood. Our research team is dedicated to an in-depth exploration of bioaerosol dynamics through metagenomic analysis. This will establish linkages between resultant environmental microbiomes and a spectrum of physico-chemical factors. We will further evaluate potential implications of climate driven bioaerosol dynamics on human health. Consequently, our research initiative entails a comprehensive analysis of bioaerosol dynamics across distinct climate regimes, encompassing alpine, temperate, and tropical environments. Using high-volumetric air sampling technologies, we have conducted environmental time series that offer high temporal and taxonomic resolution. In an interdisciplinary approach that integrates expertise from aerobiology, medicine, atmospheric physics, and climate modelling, we aim at assessing the impact of raising global temperatures on atmospheric bioaerosols and the global dispersal of airborne microorganisms. Our bioaerosol detection methodologies can be applied to both, historical and contemporary air samples, enabling to examine the bioaerosol dynamics preceding the current and most acute climate crisis. By integrating biological, chemical, and physical measurements collected from pristine alpine and metropolitan areas from temperate and tropical settings, we investigate the potential interconnections between climate-driven alterations in airborne microbial dynamics and their consequential effects on human and ecosystem health.

Biomass burning organic aerosol (BBOA) particles are a major contributor to atmospheric particulate matter, with various effects on climate and public health. Quantifying these effects is limited by our understanding of the BBOA particles' evolving chemical composition during atmospheric aging, driven by their exposure to atmospheric oxidants. This study explores the role of ozone (O3) as an atmospheric oxidant in processing primary BBOA particles. We exposed particulate emissions from beech, spruce, and pine wood fires to O3 in an oxidative flow reactor, monitoring their chemical evolution using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and extractive electrospray ionization time-of-flight mass spectrometry (EESI-ToF-MS). We found that the oxidative state of the particles increased with O3 exposure, as shown by the consistent, albeit minor, rise in O/C ratios. Analysis of the EESI-ToF-MS data revealed specific molecular groups containing 18 and 20 carbon atoms, likely mainly abietic, linoleic, and oleic acids, as highly reactive towards O3 and driving the increase in oxidative state. At higher relative humidity, increased oxidation and loss of reactive species indicate that enhanced O3 diffusion into particles allows the ozonolysis to progress further, highlighting humidity's role in overcoming diffusion barriers that limit ozonolysis in dry conditions. This study provides qualitative insights into the oxidative processing of primary BBOA particles in different phase states, presenting O3 as a selective oxidant. Further research could focus on quantifying the progression of the ozonolysis, in particular, the change in diffusion rates depending on relative humidity conditions or particle sizes.