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.

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 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.

Road traffic is an important source of urban air pollutants. Due to increasingly strict controls of exhaust emissions from road traffic, their contribution to the total emissions has strongly decreased over time in high-income countries. In contrast, non-exhaust emissions from road vehicles are not yet legislated and now make up the major proportion of road traffic emissions in many countries. Brake wear, which occurs due to friction between brake linings and their rotating counterpart, is one of the main non-exhaust sources contributing to particle emissions. Since the focus of brake wear emission has largely been on particulate pollutants, little is currently known about gaseous emissions such as volatile organic compounds from braking and their fate in the atmosphere. This study investigates the oxidative ageing of gaseous brake wear emissions generated with a pin-on-disc tribometer, using an oxidation flow reactor. The results demonstrate, for the first time, that the photooxidation of gaseous brake wear emissions can lead to formation of secondary particulate matter, which could amplify the environmental impact of brake wear emissions.

Fires in waste facilities are a common occurrence. Since many waste facilities are located adjacent to densely populated areas, these fires could potentially expose large populations to the emitted pollutants. However, at the moment there are only few field studies investigating the impact of waste fire emissions on air quality since the unpredictable nature of these events makes them challenging to capture. This study investigated the impact of a large and persistent un-prescribed fire in a waste storage facility in Stockholm county, Sweden, on the local air quality of two residential areas in close proximity to the fire. In-situ measurements of particulate matter, black carbon and nitrogen oxide concentrations were conducted both during open burning and after the fire was fully covered. In addition, filter samples were collected for offline analysis of organic composition, metal content and toxicity. Strongly increased concentrations of PM10, PM2.5 and black carbon were found during the open burning period, especially when the wind was coming from the direction of the fire. In addition, elevated concentrations of particulate heavy metals and polycyclic aromatic hydrocarbons were observed in the air during the open burning period. These results show that waste fires can have a strong impact on the air quality of nearby residential areas.

Cellular exposure to diluted exhaust gas is a promising method to assess the adverse effects of road traffic on human health. To fully understand the potential correlation between emission patterns, vehicle technologies and cellular toxicity in real-world scenarios, further research is needed. This study evaluates the toxicity of exhaust emissions from two advanced technology vehicles in real-world driving conditions. One vehicle is a gasoline direct injection (GDI) with a particle filter (GPF), while the other is a gasoline port fuel injection (PFI) hybrid without a GPF. The vehicles were tested on a chassis dyno using a Real Driving Emissions (RDE) test cycle that replicates on-road conditions. The test cycle included both cold and hot starting engine conditions. Human epithelial A549 cells were exposed to diluted exhaust using an Air Liquid Interface (ALI) system to assess toxicity. The particle dose during cell exposure simulated human inhalation in an urban environment. The ALI system was equipped with cell insert points, with or without HEPA filters, allowing the study of the effect of filtered and unfiltered exhaust. Exposed cells were subjected to Alamar Blue staining and lactate dehydrogenase (LDH) measurements were performed. The results indicate that both gaseous and particulate emissions are associated with reduction of cell viability in all cases (3-21.1%). Furthermore, higher levels of toxicity were observed during cold-start cycles of the GDI car.

Exposure to particulate matter (PM) has been associated with a wide range of adverse health effects, but it is still unclear how particles from various transport modes differ in terms of toxicity and associations with different human health outcomes. This literature review aims to summarize toxicological and epidemiological studies of the effect of ultrafine particles (UFPs), also called nanoparticles (NPs, <100 nm), from different transport modes with a focus on vehicle exhaust (particularly comparing diesel and biodiesel) and non-exhaust as well as particles from shipping (harbor), aviation (airport) and rail (mainly subway/underground). The review includes both particles collected in laboratory tests and the field (intense traffic environments or collected close to harbor, airport, and in subway). In addition, epidemiological studies on UFPs are reviewed with special attention to studies aimed at distinguishing the effects of different transport modes. Results from toxicological studies indicate that both fossil and biodiesel NPs show toxic effects. Several in vivo studies show that inhalation of NPs collected in traffic environments not only impacts the lung, but also triggers cardiovascular effects as well as negative impacts on the brain, although few studies compared NPs from different sources. Few studies were found on aviation (airport) NPs, but the available results suggest similar toxic effects as traffic-related particles. There is still little data related to the toxic effects linked to several sources (shipping, road and tire wear, subway NPs), but in vitro results highlighted the role of metals in the toxicity of subway and brake wear particles. Finally, the epidemiological studies emphasized the current limited knowledge of the health impacts of source-specific UFPs related to different transport modes. This review discusses the necessity of future research for a better understanding of the relative potencies of NPs from different transport modes and their use in health risk assessment.