The dual-spot aethalometer AE33 is a widely used instrument for measuring the aerosol absorption coefficient, but the accuracy of its measurements is heavily dependent on the multiple scattering correction factor (C), which compensates for multiple scattering effects in the filter matrix. Despite its widespread use, several aspects influencing the variability of C, particularly those related to aerosol microphysical properties, are still not fully constrained.In this work, we explore the variability of C for the AE33 in a wide range of conditions and aerosol properties by combining chamber experiments with freshly emitted laboratory-generated soot and ambient data from a mountaintop site in Italy (Monte Cimone, CMN). The C factor is derived by comparison with independent filter-based instruments such as the MAAP (Multi-Angle Absorption Photometer) and MWAA (Multi-Wavelength Absorption Analyzer) at CMN and the extinction-minus-scattering (EMS) approach in chamber experiments.The mean C value at a wavelength of 637 nm derived at CMN is 2.35 with a standard deviation of 0.58, while the average values obtained in chamber experiments in different conditions range from 2.89 +/- 0.03 to 3.9 +/- 0.06. The variability of C at CMN appears to be primarily influenced by the signal-to-noise ratio of the instruments, especially during the colder months when absorption coefficient values fall below 1 Mm-1. In contrast, in the chamber experiments, the variability is mainly driven by particle properties. The C value at 637 nm, derived from measurements at CMN, increases with increasing single scattering albedo (SSA), particularly for SSA values above 0.94, while showing no statistically significant spectral variability. Both ambient and chamber experiments highlight the dependence of the C factor on particle size, with C increasing as particle diameter decreases below 200 nm. This size dependence is relatively small (within 25 %) under ambient conditions dominated by mostly scattering aerosols, but it leads to changes greater than 60 % for highly absorbing soot particles. These results are relevant for improving the accuracy and comparability of aerosol absorption measurements performed by aethalometers, particularly within monitoring networks. The observed dependence of C on particle size suggests that differences between urban and remote sites, or between periods dominated by nucleation versus coarse-mode particles (e.g., dust), may contribute to the variability reported across locations. Understanding these dependencies is essential for refining correction approaches and reducing inter-site discrepancies in network datasets.

Per and polyfluoroalkyl substances (PFAS), a class of toxic compounds often referred to as “forever chemicals”, are increasingly detected in the atmosphere. Aerosolisation from contaminated aqueous reservoirs has been proposed as a pathway for atmospheric PFAS, drawing analogy to sea-spray processes and supported by their elevated concentrations reported near sewage treatment facilities (Kizhakkethil et al., 2025). However, aerosolisation and particle formation in anthropogenically impacted waters differ fundamentally from marine systems, and the physico chemical controls governing PFAS aerosolisation outside the marine context remain poorly understood.The aim of this work was to investigate the effect of PFAS molecular properties, including carbon chain length and functional groups, on aerosolisation from contaminated aqueous solutions. Experiments were conducted in the Chamber for Aerosol Modelling and Bio-aerosol Research (ChAMBRe), Italy. Twenty five PFAS, covering short, medium and long chain perfluoroalkyl carboxylic acids, perfluoroalkane sulfonates, fluorotelomer sulfonates and emerging alternatives representative of wastewater impacted environments were investigated. The role of bioaerosol seed particles commonly present in such environments was also assessed, as they could act as sinks or carriers for highly surface active PFAS and thereby influence their aerosol phase distribution.Aerosol mass size distributions revealed a strong dependence on molecular structure, indicating compound-specific particle-phase behaviour. The presence of biological particles did not systematically alter PFAS size-resolved distributions, suggesting that the studied PFAS exhibited limited interaction with bioaerosols and remained predominantly in the submicron size range under the investigated conditions, which may favour their atmospheric persistence and long-range transport.Overall, these findings indicate that primary aerosol formation from contaminated aqueous systems represents a chemically selective pathway for introducing PFAS into the organic aerosol, with size-resolved characteristics governed primarily by molecular properties and aerosol formation processes.Reference: Kizhakkethil, J. P., Shi, Z., Bogush, A., and Kourtchev, I.: Measurement report: Per- and polyfluoroalkyl substances (PFAS) in particulate matter (PM10) from activated sludge aeration, Atmos. Chem. Phys., 25, 5947–5958, https://doi.org/10.5194/acp-25-5947-2025, 2025.

Fine particulate matter (PM2.5) is a major air pollutant in South Asian cities; however, information on its carbonaceous composition and multi-wavelength optical properties remains limited for Lahore, Pakistan. This study investigated PM2.5 collected at an urban site in Lahore between 15 March and 29 April 2025. A total of 30 filter samples were collected; owing to sample losses during transportation, 25 filters were available for gravimetric and optical analyses, while a subset of 15 filters, selected to cover the sampling period and a broad range of PM2.5 concentrations, was used for carbonaceous aerosol analysis. Aerosol light absorption was determined using the Multi-Wavelength Absorbance Analyzer (MWAA) at five wavelengths (375, 407, 532, 635, and 850 nm). PM2.5 concentrations ranged from 40 to 417 μg m⁻³, with an average of 137 ± 84 μg m⁻³, indicating severe particulate pollution throughout the sampling period. Organic carbon was the dominant carbonaceous component, contributing 76.6% of total carbon, whereas elemental carbon accounted for 23.4%. The MWAA measurements showed the expected decrease in aerosol absorption with increasing wavelength, reflecting the spectral behaviour of carbonaceous aerosols. The average Absorption Ångström Exponent (AAE) was 1.17 ± 0.30, indicating generally weak-to-moderate wavelength dependence, with occasional enhancement of short-wavelength absorption. Based on empirical AAE intervals, 56% of the samples had values between 1.0 and 1.5, 32% had values below 1.0, and 12% exhibited values above 1.5, indicating enhanced short-wavelength absorption during a limited number of events. These intervals provide qualitative information on spectral variability rather than unambiguous source attribution. Overall, this study provides new multi-wavelength optical observations of PM2.5 from a six-week field campaign conducted in Lahore during March–April 2025 and contributes to the characterization of carbonaceous aerosols in the Indo-Gangetic Plain. The generated dataset provides a useful basis for future source-apportionment studies, air-quality management, and assessments of aerosol radiative effects in highly polluted South Asian urban environments.

Atmospheric aerosol absorption is a key parameter for assessing aerosol effects on air quality and climate, yet the comparability of absorption measurements obtained with attenuation-based and offline filter-based techniques remains uncertain under real-world conditions. This issue is particularly relevant in complex urban coastal environments, where aerosols are influenced by traffic, shipping, industrial emissions, and marine air masses. Here, we investigate this methodological comparability through a multi-wavelength field intercomparison of the AE33 Aethalometer with two independent filter-based techniques, the Multi-Wavelength Absorption Analyzer (MWAA) and the Broadband Light Analyzer of Complex Aerosols (BLAnCA), at the Multedo urban coastal site in Genoa, Italy. The three techniques showed strong correlations across the ultraviolet, visible, and near-infrared spectral regions (R2 = 0.93–0.99), with the closest agreement observed between MWAA and BLAnCA. AE33 reproduced the temporal variability in aerosol absorption well but systematically reported higher absorption coefficients than the two offline techniques, with differences of approximately 12–22% depending on wavelength. This systematic offset indicates that the default AE33 multiple-scattering correction may not fully represent the optical characteristics of the aerosol population sampled at this site. Absorption Ångström Exponent values derived independently from the three techniques remained close to unity, consistently suggesting a substantial influence of primary combustion emissions during the investigated campaign. Overall, the combined comparison of real-time and filter-based multi-wavelength techniques provides field-based evidence of their relative consistency and identifies a systematic AE33 bias that is relevant for improving the harmonization of aerosol absorption measurements in urban coastal monitoring environments.

A diverse microbiome from surface ecosystems is transported in the atmosphere, where fluctuating environmental conditions and limited nutrients challenge its survival and functioning. Among the viable bacteria frequently recovered from air are potential photoheterotrophs usually associated with vegetation. Such a specific biological trait is known to be beneficial to survival in oligotrophic environments, and we postulate here that this may contribute to the maintenance and survival during aerial transport. In this study, aerobic photoheterotrophic bacteria isolated from clouds (Methylobacterium sp. R17b-9) and expressing or lacking bacteriochlorophyll pigment, i.e., phototrophic capabilities ([Bchl +] or [Bchl-] phenotype, respectively), were injected into an atmospheric simulation chamber and monitored for their abundance, viability, cultivability and ATP content while exposed to different light intensities as aerosols. We demonstrate that phototrophy strongly enhances bacterial viability during aerial transport: whereas the fraction of cultivable cells devoid of phototrophic pigment sharply decreased under exposure to light, halving every 2 h or less, no significant loss could be observed in phototrophic cells, which also exhibited higher ATP content. The phototrophic phenotype also directly influenced the aerial dispersal range of bacteria by shortening Bchl + cells’ atmospheric residence time by a factor of 1.7, with half-times of 152 min versus 89 min, due to 8

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.

Bioaerosol is a significant element of Particulate Matter (PM) and comprises various components, with bacterial species ranking as some of the most important. Reliable and consistent bioaerosol generators are essential for the investigation of bioaerosol in laboratory environments. Aerosol generators are utilized to evaluate the performance of bioaerosol collectors, explore the transport and deposition of biological particles, and study the health impacts and exposure to airborne microorganisms. The main goal of the bacteria experiments is to have an aerosol generator able to aerosolize the maximum number of viable and culturable cells at elevated particle concentrations. This study performs a comparative investigation of two bioaerosol generators: the Sparging Liquid Aerosol Generator (SLAG) by CH Technologies and the 1520 Flow Focusing Monodisperse Aerosol Generator (FMAG) by TSI. The analysis concentrated on the vitality, culturability, fragmentation, and nebulization efficiency of E. coli cells. The results indicated increased fragmentation using the SLAG nebulizer, and the size distribution varied according to the concentration of the injection fluid for FMAG. Both nebulizers imposed significant stress on bacteria during nebulization, halving their viability. Ultimately, the nebulization efficiency of FMAG is twenty times higher than that of SLAG.

Per- and polyfluoroalkyl substances (PFAS) are recognised as atmospheric contaminants, yet processes governing their aerosol formation, size distribution, and interactions with atmospheric particle surfaces remain unknown. We investigated aerosolisation and size-resolved behaviour of 25 PFAS covering short-, medium-, and long-chain perfluoroalkyl carboxylic acids (PFCA), perfluoroalkane sulfonates, fluorotelomer sulfonates and emerging alternatives. Experiments were conducted under controlled chamber conditions using a water-organic solvent system, in the absence/presence of the model bacterium Pseudomonas fluorescens seed to investigate the potential influence of microbial presence on PFAS behaviour. Most PFAS exhibited unimodal mass-size distributions peaking at 0.3 & micro;m, indicating dominant association with the fine mode. Sulfonated PFAS showed broadly similar aerosol-phase concentrations regardless of carbon-chain length, whereas PFCA displayed increasing aerosolisation with chain length. Perfluorooctane sulfonic acid (PFOS) showed additional ultrafine enrichment, 6:2 fluorotelomer sulfonate (6:2 FTS) and sodium 4,8-dioxa-3H-perfluorononanoate (NaDONA) exhibited broader size profiles, suggesting compound-specific effects linked to volatility and interfacial behaviour. Pseudomonas fluorescens seed did not enhance PFAS aerosol concentrations through condensation or heterogeneous uptake onto bacterial particles or shift in modal diameters, and no enrichment was observed at bacterial size mode, indicating limited PFAS-bioaerosol association under the tested conditions. Multiple-Path Particle Dosimetry (MPPD) modelling based on the measured size distributions predicted substantial deposition of the aerosol-bound PFAS in the pulmonary region, particularly for compounds enriched in ultrafine particles. Our findings indicate that PFAS aerosol behaviour in mixed-solvent systems is controlled primarily by physical droplet generation and evaporation, with implications for airborne transport and inhalation exposure from contaminated aqueous sources.

This study investigated the chemical composition and shortwave absorption coefficient, β abs ( λ ), of aerosols collected from sites on the Highveld, a major industrial and highly polluted region of South Africa. Local anthropogenic mineral dust was found to be the dominant chemical component, accounting for (53 ± 14)% of the aerosol mass concentrations. Carbonaceous aerosols (34 ± 12)%, mainly from domestic and waste biomass burning, and secondary inorganic aerosols (13 ± 6%) from anthropogenic combustion sources were also found. High β abs ( λ ) was observed at all sites, with an estimated mass absorption efficiency, MAE( λ ), from (1,296 ± 472) 10 −3 m 2 g −1 at 375 nm to (621 ± 239)10 −3 m 2 g −1 at 850 nm. The contributions of the primary light‐absorbing aerosols to β abs ( λ ) were determined using chemical tracers for two optical clusters identified based on the estimated MAE for black carbon (BC). BC was the major contributor to β abs ( λ ) at all wavelengths (>60%). The brown carbon contribution decreased with λ from (8–40) % at 375 nm to (1–23) % at 532 nm, and was higher in Cluster 1 than Cluster 2. Anthropogenic mineral dust in Cluster 2 appeared to be more light absorbing than pure desert dust and was a significant contributor to β abs ( λ ), constant with wavelength at ∼16%. The levels of light‐absorbing aerosols identified have implications for the radiation budget and atmospheric stability. Although BC dominates light absorption on the South African Highveld, mineral dust contributes significantly to aerosol mass concentrations and enhanced light‐absorption.

Airborne biological particles, such as pollen, fungi, bacteria, viruses, and plant or animal detritus, are known as bioaerosols. Understanding bioaerosols’ behavior, especially their reaction to pollutants and atmospheric conditions, is crucial for addressing environmental and health issues related to air quality. Such complex investigations can benefit from experiments in controlled but realistic environments, such as the Atmospheric Simulation Chamber facility ChAMBRe (Chamber for Aerosol Modeling and Bio-aerosol Research). In this work, we report on the results of several experiments that were conducted at ChAMBRe using three strains of bacteria: E. coli, B. subtilis, and P. fluorescens. The goal of these experiments was to quantitively study how the culturability of these bacteria is affected by exposure to NO, NO2, and light. The experimental approach was simple but carefully controlled: before being introduced into ChAMBRe, the bacteria samples were characterized using three different methods to determine the ratio of viable to total bacteria. The bacteria suspension was then aerosolized and introduced into ChAMBRe, where it was exposed to two different concentrations of NO and NO2, in dark conditions and with simulated solar radiation. The culturability of the bacteria was assessed by collecting bacteria samples directly onto Petri dishes by an Andersen impactor at various time intervals after the end of injection. Finally, the formed bacteria colonies were counted after 24–48 h of incubation to measure their culturability and the temporal trend. The results show a reduction of culturability for all bacteria strains when exposed to NO2 (from 50 to 70%) and to high concentrations of NO (i.e. around 30% at more than 1200 ppb) at concentration values higher than the typical urban ambient values. Even higher effects were observed exposing the bacteria strain to a proxy of solar light. The findings show how atmospheric simulation chambers help the comprehension of interactions between pollutants and bioaerosols in controlled atmospheric environments.

Soot aerosol generated from the incomplete combustion of biomass and fossil fuels is a major light-absorber; however its spectral optical properties for varying black carbon (BC) and brown carbon (BrC) content remain uncertain. In this study, soot aerosols with varying maturity and composition, i.e. elemental-to-total-carbon ratio (EC/TC), have been studied systematically in a large simulation chamber to determine their mass absorption, scattering, and extinction cross sections (MAC, MSC, MEC); single-scattering albedo (SSA); and absorption and scattering & Aring;ngstr & ouml;m exponents (AAE, SAE). The MAC, MEC, SSA, and AAE show a variability between the different types of soot with varying EC/TC ratios. The MAC (MEC) at 550 nm increases for increasing EC/TC, with values of 1.0 (1.4) m2 g-1 for EC/TC = 0.0 (BrC-dominated soot) and 4.6 (5.1) m2 g-1 for EC/TC = 0.79 (BC-dominated soot). The AAE and SSA (550 nm) decrease from 3.79 and 0.29 (EC/TC = 0.0) to 1.27 and 0.10 (EC/TC = 0.79). Combining present results for soot from propane combustion with literature data for flame soot from diverse fuels supports a generalised exponential relationship between particle EC/TC and its MAC and AAE values (MAC550=(1.3 +/- 0.05) e(1.8 +/- 0.1)ECTC; AAE=(0.73 +/- 0.12)+(3.29 +/- 0.12) e-(2.32 +/- 0.30)ECTC), which represents the optical continuum of spectral absorption for soot with varying maturity. From this, it is possible to extrapolate a MAC of 7.9 and 1.3 m2 g-1 (550 nm) and an AAE (375-870 nm) of 1.05 and 4.02 for pure EC (BC-like) and pure OC (BrC-like) soot. The established relationship can provide a useful parameterisation for models to estimate the absorption from combustion aerosols and their BC and BrC contributions.

South Africa, with its industrialised economy, faces unique air pollution challenges. Our study investigates aerosol composition and absorption in the Highveld region. Understanding aerosol absorption is critical as it affects climate, air quality, and public health. Aerosol absorption in the lower atmosphere affects the evolution of the boundary layer and the dispersion of pollutants, which in turn affects air quality and public health. Aerosol filter samples (PM10 fractions) were collected from residential, traffic, and industrial sites during the dry season. Chemical analyses, including X-ray fluorescence, thermo-optical analysis, and ion chromatography, were carried out to determine elemental species, carbonaceous species, and water-soluble ions, respectively. Based on this, a mass closure calculation was performed to define the contribution of five major aerosol components. The calculated aerosol mass concentrations were in good agreement with the measurements (Normalised Mean Bias, NMB < 7%). No significant variation in PM10 concentration was observed between site types. Mineral dust appeared to be the main contributor to PM10, varying from about 48%-60% at different sites, followed by organic matter (OM, 22%-35%), secondary inorganic aerosols (SIA, 9%-12%), elemental carbon (EC, 4%-7%), and sea salt (ss, 1%-2%). Aerosol spectral absorption was obtained from multi-wavelength absorbance analysis (MWAA) measurements at 375, 407, 532, 635, and 850 nm. High absorption was measured in the following order: industrial> residential> traffic sites. The estimated absorption Ångström exponent (AAE) varied from 0.8 to 2 at different sites, indicating the contribution of several sources. At 850 nm absorption correlates well with EC as expected (r = 0.85). The obtained mass absorption efficiency (8 m2/g) is in line with expectations. Specific tracers were used to determine the contribution of the main absorbing aerosol components - black carbon (BC), brown organic carbon (BrC) from incomplete biomass combustion, and mineral dust - using correlations between estimated mass and measured absorption. Preliminary results indicate that although BC is the major contributor to absorption, accounting for 30%-60% absorption at 375 nm, followed by BrC 10%-50%, the contribution of the less absorbing but more abundant mineral dust is not negligible and can range from 2% to 50% in different samples. These results underline the complexity of aerosols in the region and their high absorption properties, and the need for a comprehensive understanding of its various components to accurately assess its impact.

Bioaerosol is generally defined as solid airborne particles of biological origin suspended in the gaseous medium ubiquitously with an aerodynamic diameter of up to 100 µm. They can either be naturally released from the biosphere to the atmosphere or are released due to human activities. Here, we present the results of several experiments, performed inside a confined and controlled artificial environment, such as the Atmospheric Simulation Chamber, providing valuable information on bio-aerosol viability, dispersion, and impact. At ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research), managed by INFN at the Physics Department of the University of Genoa, Italy, the research on bioaerosol is focused on the investigation of the airborne bacteria behavior in different atmospheric and air quality conditions (Massabò et al., 2018). A multi-step protocol was developed (Vernocchi et al, 2023) and thoroughly tested to cultivate a suitable bacteria population (E. coli, B. subtilis, B. licheniformis, and P. fluorescens). Then, bacteria are nebulized, and injected inside ChAMBRe, where they are exposed to different gas concentration values. The viability variation, due to the pollutant exposure inside ChAMBRe, was determined by monitoring the concentration of viable bacteria. The bacteria survival rate inside ChAMBRe is first evaluated by a set of baseline experiments (clean air condition) and successively exposing the bacterial strands to NO2 and NO concentration values up to 1200 ppb for both pollutants. A WIBS-NEO instrument measured bacteria total concentration inside ChAMBRe while the viable concentration was determined by active sampling on Petri dishes by an Andersen impactor and then counting the Colonies Forming Units (CFU). In addition, a liquid impinger was used to maintain the integrity of the microorganisms and their physiological state to investigate a sampling strategy to assess viability and simultaneously cultivability, taking into account the VBNC status (viable but not cultivable). To this end, we present the results of impactor experiments and preliminary assessments with live and dead assays examined by fluorescence microscopy for quantitative and qualitative analysis.ReferencesMassabò, D., Danelli, S. G., Brotto, P., Comite, A., Costa, C., Di Cesare, A., Doussin, J. F., Ferraro, F., Formenti, P., Gatta, E., Negretti, L., Oliva, M., Parodi, F., Vezzulli, L., and Prati, P.: ChAMBRe: a new atmospheric simulation chamber for aerosol modelling and bio-aerosol research, Atmos. Meas. Tech., 11, 5885–5900, https://doi.org/10.5194/amt-11-5885-2018, 2018.Vernocchi, V., Abd El, E., Brunoldi, M., Danelli, S. G., Gatta, E., Isolabella, T., Mazzei, F., Parodi, F., Prati, P., and Massabò, D. (2023) Atmos. Meas. Tech., 16, 5479–5493. https://doi.org/10.5194/amt-16-5479-2023, 2023.

We introduce a new instrument to measure spectral light absorption by aerosol particles. BLAnCA (Broadband Light Analyzer of Complex Aerosol) is an automatic laboratory instrument for offline measurement of aerosol collected on suitable media. BLAnCA is equipped with a white light source and a high-resolution spec-trometer, and measures in the range between 375 and 1000 nm with a spectral resolution of 5 nm. This allows for the determination of fine structure of the ab-sorption properties of a sampled aerosol, which can lead to improvement in the robustness and scope of source apportionment and the evaluation of climate-relevant properties such as the aerosol mass absorption cross-section. The new instrument has been validated against a multi-wavelength absorbance analyzer, obtaining an agreement of up to 99 % between absorption coefficient measurements. The absorption coefficient limit of detection for BLAnCA has been estimated at 1.20 Mm-1 (2.70 Mm-1 ) for standard EU (EPA) sampling conditions, corresponding to an elemental carbon detection limit of about 1.3 mu g cm-2 , if a mass absorption cross-section of 4.7 m 2 g-1 at 1000 nm is considered. The instrument has been used to characterize several types of aerosol samples, each with its own distinct absorp-tion features, which show the potential for BLAnCA to identify different kinds of particulate matter based on their optical properties.

This study investigates how chemical composition, atmospheric aging, and environmental conditions affect the oxidative potential (OP) and cellular toxicity of soot particles using an atmospheric simulation chamber (ASC). In the ASC ChAMBRe were simulated real-world summer and winter scenarios, exposing pure soot particles (generated by using the mini-inverted soot generator) and various secondary aerosol precursors (i.e., toluene, 2,5-dimethylfuran and α-pinene) alternatively to light or dark conditions and different oxidants. OP was assessed using multiple assays (namely, 2',7'-dichlorofluorescein - DCFH, Dithiothreitol - DTT and Ascorbic Acid - AA), revealing that soot particles exposed to light, especially in presence of toluene, exhibited higher OP. The presence of toluene also increased cellular reactive oxygen species (ROS) production, leading to elevated cytotoxicity, DNA damage, and release of the proinflammatory cytokine interleukin-8 (IL-8) in BEAS-2B cells. Ammonium sulfate addition reduced OP and do not enhance toxicological responses, suggesting that non-toxic components in aged particulate matter (PM) may mitigate some harmful effects. Toxicological assessment showed increased cytotoxicity, genotoxicity, oxidative stress, and inflammatory responses in soot generated under high irradiance conditions typical of summer and traffic environments, compared to low irradiance winter scenarios. Strong correlations were observed between OP and toxicological endpoints, such as ROS formation, LDH release, micronuclei formation, and IL-8 secretion underscoring the role of chemical composition and environmental aging in determining PM toxicity. The study highlights OP assays as a reliable tool for predicting PM-induced oxidative stress and potential health effects, emphasizing the importance of considering soot chemical composition and aging processes in urban air pollution assessments.

Abstract. The joint use of hourly resolution sampling and analyses with accelerated ion beams such as Particle Induced X-ray Emission (PIXE) technique has allowed the measurement of hourly temporal patterns of particulate matter (PM) composition at many sites in different parts of the world. The demand within the scientific community for this type of analysis has been continuously increasing in recent years, but hourly resolution samplers suitable for PIXE analysis are now discontinued and/or suffer from some technical limitations. In this framework, a new hourly sampler, STRAS (Size and Time Resolved Aerosol Sampler), was developed for the collection of PM10, PM2.5 or PM1. It allows automatic sequential sampling of up to 168 hourly samples (1 week), it is mechanically robust, compact, and easily transportable. To increase PIXE sensitivity, each sample is concentrated on a small surface area on a polycarbonate membrane. The comparison between the elemental concentrations retrieved by STRAS samples and samples collected using a standard sequential sampler operated in parallel shows a very good agreement; indeed, if both the samplers use the same kind of membrane, the concentrations of all detected elements are in agreement within 10 %.

In this paper, we applied the Dispersion Normalised Positive Matrix Factorisation (DN-PMF) approach recently proposed in the literature to provide a more realistic picture of the relative importance of emission strength vs. atmospheric dispersion conditions. The disentanglement of such effects is of great concern in pollution hot spots like the Po Valley (Italy), where particulate matter limit values are exceeded despite the existing abatement measures. To explore the potentiality of the DN-PMF approach - still scarcely applied in the literature - a well -chemically characterised PM1 (atmospheric particles with aerodynamic diameter <1 mu m) dataset comprising samples collected at different time resolutions at an urban background site (Bologna) in the southern Po Valley was used. Indeed, it is well known that shallow mixing layers promote pollutant accumulation but this obser-vation is not enough to exclude an enhancement of emission strength which could be tackled by appropriate abatement strategies.The source apportionment of sub-micron sized aerosols having a quite long atmospheric residence time in a complex environment like the Po Valley -which is also strongly impacted by secondary aerosol formation on a basin-scale -is generally quite challenging when using receptor models. Due to the availability of a huge dataset with variables having multiple time resolutions, in this work the DN-PMF was implemented in a multi-time resolution approach (MT) to achieve a better source identification and to gain knowledge about the relative importance of atmospheric dilution vs. emissions. A comparison between results obtained by the application of the regular multi time resolution (REG-MT) vs. the DN-MT approach is presented here for the five factors identified (nitrate-dominated, sulphate-dominated, biomass burning, mineral dust, and urban aerosol). The first interesting outcome is that REG-MT and DN-MT results do not point at significant differences in temporal pat-terns for aerosol components and sources impacting at the basin-scale (i.e. sulphate-and nitrate-dominated aerosol, biomass burning) thus suggesting that the diel modulation of these PM1 emissions is somehow masked by the stronger variability of the mixing layer. Conversely, contributions from local sources with more pronounced diel variation like traffic are quite well reproduced by DN-MT and the ambient concentrations are enhanced compared to REG-MT. This is an important piece of information highlighting that PM1 concentrations from local sources have been likely underestimated by REG-MT assessments.To our knowledge, this is one of the very few applications of DN-MT and the first one at a European site where the huge effort made to implement air pollution containment measures is still not very much effective in reducing PM levels; moreover, in this paper a detailed discussion about the possible interpretation of the output of DN-MT in terms of temporal patterns is reported.

Instruments measuring aerosol light absorption, such as the Aethalometer and the Multi-Wavelength Absorbance Analyzer (MWAA), have been extensively used to characterize optical absorption of atmospheric particulate matter. Data retrieved with such instruments can be analysed with mathematical models to apportion different aerosol sources (Aethalometer model) and components (MWAA model). In this work we present an upgrade to the MWAA optical apportionment model. In addition to the apportionment of the absorption coefficient babs in its components (black carbon and brown carbon) and sources (fossil fuels and wood burning), the extended model allows for the retrieval of the absorption Ångström exponent of each component and source, thereby avoiding initial assumptions regarding these parameters. We also present a new open-source software toolkit, the MWAA model toolkit (MWAA_MT), written in both Python and R, that performs the entire apportionment procedure.

The effects of bioaerosol, the biological component of atmospheric aerosol, on the environment and health are numerous but still little known, studies on the subject are continually growing. Experiments conducted in Atmospheric Simulation Chambers (ASCs), can provide valuable information on the viability, dispersion and interactions of microorganisms in the aerosols. For this purpose, a multi-step experimental procedure was developed; systematic studies have been carried out in our ASC, to expose bioaerosol to controlled atmospheric conditions. This study reports the results of the experiments conducted on Escherichia coli and Bacillus subtilis, , which highlight how the two bacterial strains react, in terms of viability, to the aerosolization process and to remaining in an aerosolized state in controlled atmospheric conditions.