Air pollution adversely affects human health, with studies consistently linking it to exposure to particulate matter. However, differential toxicity remains to be established to improve monitoring and mitigation efforts. This study examines the oxidative potential (OP) of fine particulate matter using the dithiothreitol (DTT) assay as a proxy for toxicity. We analyzed 42 ambient particle filter samples from Frankfurt, Germany, and Beijing, China, focusing on water-soluble organic compounds. The aqueous extracts were analyzed for metal content via inductively coupled plasma–mass spectrometry and for organic compounds through ultrahigh performance liquid chromatography–high-resolution mass spectrometry. Utilizing a chelating agent to remove metals allowed separation of the effects of bulk aerosol and organics only. A hierarchical cluster analysis identified key compounds linked to OP, including yet unknown quinones, C₉H₆O₆ (an oxidation product of o-xylene), and C₉H₈O₄ (an oxidation product of trimethylbenzene), suggesting secondary products from aromatic precursors. We also found phthalic acid, a tracer for biomass burning and vehicular exhaust, and nitrosalicylic acid, an OP-enhancing compound. A volume-normalized OP of up to 4 nmol DTT min^–1 m^–3 was observed after metal removal, underscoring the importance of stable organic compounds and isolating metals to understand their relationship with OP in ambient particulate matter.

This paper presents the findings from a collaborative interlaboratory comparison exercise designed to assess oxidative potential (OP) measurements conducted by 20 laboratories worldwide. This study represents an innovative effort as the first exercise specifically aimed at harmonising this type of OP assay, setting a new benchmark in the field. Over the last decade, there has been a noticeable increase in OP studies, with numerous research groups investigating the effects of exposure to air pollution particles through the evaluation of OP levels. However, the absence of standardised methods for OP measurements has resulted in variability in results across different groups, rendering meaningful comparisons challenging. To address this issue, this study engages in an international effort to compare OP measurements using a simplified method (with a dithiothreitol (DTT) assay). Here, we quantify the OP in liquid samples to focus on the protocol measurement itself, while future international OP interlaboratory comparisons (ILCs) should aim to assess the whole chain process, including the sample extraction. We analyse the similarities and discrepancies observed in the results, identifying the critical parameters (such as the instrument used, the use of a simplified protocol, the delivery and analysis time) that could influence OP measurements and provide recommendations for future studies and interlaboratory comparisons even if other crucial aspects, such as sampling PM methods, sample storage, extraction methods and conditions, and the evaluation of other OP assays, still need to be standardised. This collaborative approach enhances the robustness of the OP DTT assay and paves the way for future studies to build on a unified framework. This pioneering work concludes that interlaboratory comparisons provide essential insights into the OP metric and are crucial to move toward the harmonisation of OP measurements.

This study investigated the impact of Diesel Particulate Filter (DPF) regeneration on the composition and toxicity of exhaust emissions from a Euro 6d diesel passenger vehicle. Multiple real-world–simulated driving cycles were performed under two DPF conditions: normal operation and active regeneration. Exhaust emissions were characterized in real time for gaseous and particulate pollutants, while the nanoparticle fraction of the particulate mass was chemically analyzed for its organic and inorganic components. The toxicological effects of DPF regeneration were evaluated using an in vitro Air–Liquid Interface (ALI) exposure system with human lung cells. The results indicate that DPF regeneration accounted for more than 95 % of total particle number emissions, while significant amounts of carbon monoxide and methane were emitted as well. Exposures in the absence of particles led to similar reductions in cell viability and inflammatory responses, regardless of the DPF condition. In contrast, when particles were present, the cellular response became significantly stronger, indicating that the increased toxicity is primarily driven by the particulate fraction. Chemical analyses of nanoparticle mass revealed higher concentrations of water-soluble elements and oxygenated polycyclic aromatic hydrocarbons during regeneration. Overall, DPF regeneration transiently but substantially alters emission characteristics and significantly increases their toxicological potential.

Uncontrolled waste burning and accidental waste fires are an important source of emissions into the air. However, there are currently only few field studies providing data on these emissions. In this study, we investigated the emission rates, pollutant dispersion and particle composition for a large waste fire in Stockholm county, Sweden. Our results show that the waste fire, while burning, may have contributed as much as 5 times the mean PM₁₀ emissions from road traffic of the municipality it was located in (ca 95 000 inhabitants), which highlights the potential impact of temporary events such as waste fires on air quality. Gaussian dispersion calculations were used to model the spatial distribution of measured PM₁₀ data, demonstrating its use for assessment of exposure and deposition. Particles impacted by the waste fire were enriched in several potentially toxic metals and metalloids including arsenic, copper, cadmium and, in particular, lead when compared to particles collected after the fire. In addition, they may also pose an increased cancer risk on a per-mass basis compared to the post-fire period due to the larger mass fraction of relevant PAHs.

The emission of volatile organic compounds (VOCs) from brake wear is a relatively underexplored aspect of nonexhaust traffic emissions. We employed a proton-transfer-reaction time-of-flight mass spectrometer to investigate the real-time emissions of VOCs from two commercially prevalent brake materials: low-metallic copper-free (LMCF) and nonasbestos organic (NAO). Experiments were conducted using a pin-on-a-disc tribometer integrated with a fast-mobility particle sizer spectrometer. The results reveal that NAO brake pads emit higher concentrations of VOCs than LMCF pads. Over 200 different sum formulas were identified for both materials, and siloxanes were observed as characteristic of NAO emissions. The ultrafine particle formation was systematically preceded by an increase in gaseous emissions. This observation supports the thesis that ultrafine particle formation emitted by brake wear occurs through VOCs nucleation, addressing a significant gap in the literature.

The Italian Po Valley is one of the most polluted regions in Europe. During winter, meteorological conditions favor long and dense fogs, which strongly affect visibility and human health. In spring, the frequency of nighttime fogs reduces while daytime new particle formation events become more common. This transition is likely caused by a reduction in particulate matter (PM_2.5), leading to a decrease in the relevant condensation sink. The physics and chemistry of fog and aerosol have been studied at the San Pietro Capofiume site since the 1980s, but the detailed processes driving the observed trends are not fully understood. Hence, during winter and spring 2021/22, the Fog and Aerosol Interaction Research Italy (FAIRARI) campaign was carried out, using a wide spectrum of approaches, including in situ measurements, outdoor chamber experiments, and remote sensing. Atmospheric constituents and their properties were measured ranging from gas molecules and molecular clusters to fog droplets. One unique aspect of this study is the direct measurement of the aerosol composition inside and outside of fog, showing a slightly greater dominance of organic compounds in the interstitial compared to the droplet phase. Satellite observations of fog provided a spatial context and agreed well with in situ measurements of droplet size. They were complemented with in situ chamber experiments, providing insights into oxidative processes and revealing a large secondary organic aerosol-forming potential of ambient air upon chemical aging. The oxidative potential of aerosol and fog water inferred the impact of aerosol–fog interactions on particle toxicity.

Exposure to airborne particulate matter (PM) has been attributed to millions of deaths annually. However, the PM components responsible for observed health effects remain unclear. Oxidative potential (OP) has gained increasing attention as a key property that may explain PM toxicity. Using online measurement methods that impinge particles for OP quantification within seconds, we reveal that 60 to 99% of reactive oxygen species (ROS) and OP in secondary organic aerosol and combustion-generated PM have a lifetime of minutes to hours and that the ROS activity of ambient PM decays substantially before offline analysis. This implies that current offline measurement methods substantially underestimate the true OP of PM. We demonstrate that short-lived OP components activate different toxicity pathways upon direct deposition onto reconstituted human bronchial epithelia. Therefore, we suggest that future air pollution and health studies should include online OP quantification, allowing more accurate assessments of links between OP and health effects.

Traffic-related air pollution is a major public health concern, contributing to respiratory and cardiovascular diseases worldwide. The aim of this study was to investigate the feasibility of using a mobile Air-Liquid Interface (ALI) system to assess the cytotoxicity and inflammatory potential of freshly generated PM_2.5 (particle matter with aerodynamic diameter <2.5 μm) in a road tunnel in Stockholm. We hypothesized that cellular effects would be detectable at lower doses compared to submerged exposures. The mean particle dose in ALI was 1.4 ± 0.8 μg/cm², whereas a wide range of doses was used for submerged exposures. ALI and submerged results showed that PM_2.5 from the road tunnel did not affect the viability of A549 cells, whereas a significant and dose-dependent decrease in viability of dTHP-1 (in submerged exposure) was observed. Furthermore, in A549 in ALI a slight increase in inflammatory response (IL-8, IL-6, and IL-1β) was observed. In submerged exposure, the inflammatory response was clearer, particularly in the dTHP-1 cells. In conclusion, this study presents the first successfully conducted in situ ALI exposure in a road tunnel. The results demonstrate that dTHP-1 cells exhibit clear cytotoxic and inflammatory responses, while A549 show only weak effects. These findings suggest that co-cultures of A549 and dTHP-1 may be valuable in future ALI studies.

Nanoparticles (ultrafine particles) are prevalent in various environments and raise concerns due to their potential health effects. In this study, we aimed to enhance the understanding of the toxicity associated with nanoparticles generated within subway systems. Specifically, we investigated nanoparticles produced using spark discharge from electrodes made of the same material as the third rail (which provides electric power), rail, and wheel components in the Stockholm subway system. Characterization revealed that the generated nanoparticles typically had a primary size of 6–10 nm and exhibited high agglomeration. They consisted mainly of iron, along with varying amounts of manganese and silicon. Despite having low oxidative potential, they showed some cytotoxicity and clearly induced DNA strand breaks in both dTHP-1 cells (monocyte-derived macrophages) and A549 cells (lung epithelial cells). In addition, gene expression analysis showed an upregulation of the cytokine IL-8 in dTHP-1 cells. No increased release of IL-1β, IL-8, IL-6, and TNF-a was noted. Consistent differences in toxicity between the nanoparticles from different materials were not observed. In conclusion, the results show that subway-related nanoparticles can cause DNA damage in cultured lung cells, but the inflammatory potential in terms of cytokine release was limited.