Spatial and seasonal heterogeneity of atmospheric particles induced reactive oxygen species in urban areas and the role of water-soluble metals

Laboratory study on the characteristics of fresh and aged PM1 emitted from typical forest vegetation combustion in Southwest China

The frequency and intensity of forest fires are amplified by climate change. Substantial quantities of PM1 emitted from forest fires can undergo gradual atmospheric dispersion and long-range transport, thus impacting air quality far from the source. However, the chemical composition and physical properties of PM emitted from forest fires and its changes during atmospheric transport remain uncertain. In this study, the evolution of organic carbon (OC), elemental carbon (EC), water-soluble ions, and water-soluble metals in the particulate phase of smoke emitted from the typical forest vegetation combustion in Southwest China before and after photo-oxidation was investigated in the laboratory. Two aging periods of 5 and 9 days were selected. The OC and TC mass concentrations tended to decrease after 9-days aged compared to fresh emissions. OP, OC2, and OC3 in PM1 are expected to be potential indicators of fresh smoke, while OC3 and OC4 may serve as suitable markers for identifying aged carbon sources from the typical forest vegetation combustion in Southwest China. K+ exhibited the highest abundant water-soluble ion in fresh PM1, whereas NO3- became the most abundant water-soluble ion in aged PM1. NH4NO3 emerged as the primary secondary inorganic aerosol emitted from typical forest vegetation combustion in Southwest China. Notably, a 5-day aging period proved insufficient for the complete formation of the secondary inorganic aerosols NH4NO3 and (NH4)2SO4. After aging, the mass concentration of the water-soluble metal Ni in PM1 from typical forest vegetation combustion in Southwest China decreased, while the mean mass concentrations of all other water-soluble metals increased in varying degrees. These findings provide valuable data support and theoretical guidance for studying the atmospheric evolution of forest fire aerosols, as well as contribute to policy formulation and management of atmospheric environment safety and human health.

Size-segregated characteristics of water-soluble oxidative potential in urban Xiamen: Potential driving factors and implications for human health

Oxidative potential (OP), defined as the ability of particulate matter (PM) to generate reactive oxygen species (ROS), has been considered as a potential health-related metric for PM. Particles with different sizes have different OP and deposition efficiencies in the respiratory tract and pose different health risks. In this study, size-segregated PM samples were collected at a coastal urban site in Xiamen, a port city in southeastern China, between August 2020 and September 2021. The water-soluble constituents, including inorganic ions, elements and organic carbon, were determined. Total volume-normalized OP based on the dithiothreitol assay was highest in spring (0.241 ± 0.033 nmol min-1 m-3) and lowest in summer (0.073 ± 0.006 nmol min-1 m-3). OP had a biomodal distribution with peaks at 0.25-0.44 μm and 1.0-1.4 μm in spring, summer, and winter and a unimodal pattern with peak at 0.25-0.44 μm in fall, which were different from the patterns of redox-active species. Variations in the seasonality of fine and coarse mode OP and their correlations with water-soluble constituents showed that the size distribution patterns of OP could be attributed to the combined effects of the size distributions of transition metals and redox-active organics and the interactions between them which varied with emissions, meteorological conditions and atmospheric processes. Respiratory tract deposition model indicated that the deposited OP and the toxic elements accounted for 47.9 % and 36.8 % of their measured concentrations, respectively. The highest OP doses and the excess lifetime carcinogenic risk (ELCR) were found in the head airway (>70 %). However, the size distributions of OP deposition and ELCR in the respiratory tract were different, with 63.9 % and 49.4 % of deposited ELCR and OP, respectively, coming from PM2.5. Therefore, attention must be paid to coarse particles from non-exhaust emissions and road dust resuspension.

Contribution of water-soluble extracts to the oxidative and inflammatory effects of atmospheric aerosols: A critical review

Exposure to atmospheric particulate matter (PM) has been associated with heightened risks of lung cancer, cardiovascular and respiratory diseases. PM exposure also affects the immune system, leading to an increased susceptibility to infections, exacerbating pre-existent inflammatory and allergic lung diseases. Atmospheric PM can primarily impact human health through the generation of reactive oxygen species (ROS) that subsequently induce or exacerbate inflammation. These cytotoxic effects have been related with PM concentration, and its chemical constituents, including metals, solvent extractable organics (e.g., polycyclic aromatic hydrocarbons), and water-soluble ions. Although not receiving much attention, the fine aerosol water-soluble organic matter (WSOM) can account for a substantial portion of the overall fine PM mass and has been shown to present strong oxidative and immunomodulatory effects. Thus, the objective of this review is to provide a comprehensive analysis of the role of the water-soluble fraction of PM, with a specific focus on the contribution of the WSOM component to the cytotoxic properties of atmospheric PM. The chemical properties of the water-soluble PM fraction are briefly discussed, while emphasis is put on how PM size, composition, and temporal variations (e.g., seasonality) can impact the pro-oxidative activity, the modulation of inflammatory response, and the cytotoxicity of the water-soluble PM extracts.

Size-segregated source identification of water-soluble and water-insoluble metals and trace elements of coarse and fine PM in central Los Angeles

In this study, the water-solubility and sources of metals and trace elements in both fine and coarse particulate matter (PM) were investigated in Central Los Angeles. Sampling was performed in the winter, spring, and summer of 2022 at the Particle Instrumentation Unit (PIU) of the University of Southern California located in the proximity of I-110 freeway. Both fine and coarse PM samples were collected using Personal Cascade Impactors (PCIS) and chemically analyzed to determine their water-soluble and water-insoluble metal content. Principal Component Analysis (PCA) and Multiple Linear Regression (MLR) were used to determine the sources of soluble and insoluble metals and obtain their contributions to total metal concentration. Our results indicate that the water-solubility of most of the metals is higher in the fine size fraction compared to the coarse fraction. Seasonal variations in the water solubility of selected metals for both coarse and fine fractions were observed, with higher water-soluble metal concentrations in summer for several species (e.g., Fe , S, Pb, Cu, La, Ni, and Al ), possibly due to higher photochemical processing, while in winter, almost all species exhibited higher insoluble fraction concentrations. The PCA and MLR analyses results showed that tire and brake wear was the most significant contributor to the total metals for both fine soluble and insoluble portions, accounting for 35% and 75% of the total metals, respectively. Combustion sources also contributed substantially to water-soluble metals for fine and coarse size ranges, representing 40% and 32% of the total metal mass, respectively. In addition, mineral dust and soil and re-suspended dust were identified as the highest contributors to coarse metals. The MLR analysis also revealed that secondary aerosols contributed 11% to the fine water-soluble metals. Our results suggest that non-tailpipe emissions significantly contribute to both coarse and fine PM metals in the Central Los Angeles region.

Chemical Characteristics and Cytotoxicity to GC-2spd(ts) Cells of PM2.5 in Nanjing Jiangbei New Area from 2015 to 2019

PM_2.5 is an air pollutant with complex components. After entering the body through respiration, PM_2.5 can not only cause respiratory diseases, but also break through the blood-testis barrier and influence the reproductive system. PM_2.5 with different components may result in different toxic effects. In the first five years of Nanjing Jiangbei New Area, industrial transformation would change the concentration and chemical fraction of PM_2.5 in the local environment to a certain extent. In this study, PM_2.5 collected in Nanjing Jiangbei New Area every autumn and winter from 2015 to 2019 was analyzed. PM_2.5 concentration generally decreased year by year. The large proportion of secondary inorganic ions indicated the presence of secondary pollution at the sampling site. PM_2.5 was mainly emitted from fossil fuel combustion and vehicle exhaust. The cytotoxicity of PM_2.5 samples was evaluated by PM_2.5 exposure to mouse spermatocytes (GC-2spd(ts) cells). Cell viability was relatively low in 2016 and 2018, and relatively high in 2017 and 2019. Reactive oxygen species levels and DNA damage levels followed similar trends, with an overall annual decrease. The cytotoxicity of PM_2.5 on GC-2spd(ts) cells was significantly correlated with water-soluble ions, water-soluble organic carbon, heavy metals and polycyclic aromatic hydrocarbons (p < 0.01). According to principal component analysis and multiple linear regression, fossil fuel combustion, secondary transformation of pollutants and construction dust were identified as the major contributors to cytotoxic effects, contributing more than 50%.

Optical properties, molecular characterizations, and oxidative potentials of different polarity levels of water-soluble organic matters in winter PM2.5 in six China's megacities

Humic-like substances (HULIS) accounted for a great fraction of water-soluble organic matter (WSOM) in PM_2.5, which efficiently absorb ultraviolet (UV) radiation and pose climate and health impacts. In this study, the molecular structure, optical properties, and oxidative potential (OP) of acid- and neutral-HULIS (denoted as HULIS-a, and HULIS-n, respectively), and high-polarity WSOM (HP-WSOM) were investigated in winter PM_2.5 collected at six China's megacities. For both carbon levels and optical absorption coefficients (b_{abs_365}), HULIS-a/HULIS-n/HP-WSOM showed significant spatial differences. For each city, the carbon levels and b_{abs_365} follow a similar order of HULIS-n > HULIS-a > HP-WSOM. Besides, the b_{abs_365} of HULIS-n and HULIS-a showed the same order of Harbin > Beijing ≈ Wuhan > Xi'an > Guangzhou > Chengdu, while HP-WSOM exhibited an order of Wuhan > Chengdu > Xi'an > Harbin > Beijing > Guangzhou. Both HULIS-a and HULIS-n were abundant in aromatic and aliphatic compounds, whereas HP-WSOM was dominated by a carboxylic acid group. The OP (in unit of nmol H₂O₂ μg^-1C) followed the order of HP-WSOM > HULIS-a > HULIS-n in all the cities. The OPs of HULIS-a, HULIS-n, and HP-WSOM in Harbin and Beijing were much higher than those of other cities, attributing to the high contribution from biomass burning. Highly positive correlations between reactive oxygen species (ROS) of HULIS-a and MAE₃₆₅ were obtained in Chengdu, Wuhan, and Harbin, but ROS of HULIS-n had stronger correlation with MAE₃₆₅ in Harbin, Chengdu, and Xi'an.

Role of semi-volatile particulate matter in gas-particle partitioning leading to change in oxidative potential

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM_2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM_2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200 °C) to characterize PM physico-chemical properties. While the mass concentrations of PM_2.5 and p-PAHs reduced to ∼34% at 200 °C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200 °C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50 °C, 100 °C, and 200 °C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200 °C. This provided a good estimate of the contribution of SVOCs in ROS production in PM_2.5, where decreased SVOCs concentration at 200 °C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

Effects of atmospheric aging processes on in vitro induced oxidative stress and chemical composition of biomass burning aerosols

Biomass burning (BB) has an important impact on local/regional air quality and human health in China, but most previous studies overlooked the influence of atmospheric aging processes on cytotoxicity and chemical composition of BB aerosols. In this study, we combined a combustion chamber and an oxidation flow reactor to generate fresh and aged BB PM_2.5. Human bronchial epithelial BEAS-2B cells were exposed to PM_2.5 preparation for 24 h, and then determined for particle-induced reactive oxygen species (ROS) in vitro. The particle-induced ROS production increased by 11 %-64 % after two days of aging, suggesting an enhancement of in vitro-induced oxidative stress (OS) of aged BB particles. Chemical analysis showed that organic matter (OM) was the dominant component with no changes in relative abundance for the fresh and aged BB particles. Organic polycyclic aromatic compounds and some metals showed strong correlations with ROS in fresh particles, indicating the important effects of these harmful components on the OS of fresh BB aerosols. However, such correlations were not found for the aged particles, which is possibly related to the loss of non- or low-toxic semivolatile compounds and the formation of secondary harmful OM (such as some N-containing organic compounds) during the atmospheric aging processes.

Characteristics and toxicological effects of commuter exposure to black carbon and metal components of fine particles (PM2.5) in Hong Kong

Epidemiological studies have demonstrated significant associations between traffic-related air pollution and adverse health outcomes. Personal exposure to fine particles (PM_2.5) in transport microenvironments and their toxicological properties remain to be investigated. Commuter exposures were investigated in public transport systems (including the buses and Mass Transit Railway (MTR)) along two sampling routes in Hong Kong. Real-time sampling for PM_2.5 and black carbon (BC), along with integrated PM_2.5 sampling, were performed during the warm and cold season of 2016-2017, respectively. Commuter exposure to BC during 3-hour commuting time exhibited a wider range, from 3.4 to 4.6 μg/m³ on the bus and 5.5 to 8.7 μg/m³ in MTR cabin (p < .05). PM_2.5 mass and major chemical constituents (including organic carbon (OC), elemental carbon (EC), and metals) were analyzed. Cytotoxicity, including cellular reactive oxygen species (ROS) production, was determined in addition to acellular ROS generation. PM_2.5 treatment promoted the ROS generation in a concentration-dependent manner. Consistent diurnal variations were observed for commuter exposure to BC and PM_2.5 components, along with cellular and acellular ROS generation, which marked with two peaks during the morning (08:00-11:00) and evening rush hours (17:30-20:30). Commuter exposures in the MTR system were characterized by higher levels of PM_2.5 and elemental components (e.g., Ca, Cr, Fe, Zn, Ba) compared to riding the bus, along with higher cellular and acellular ROS production (p < .01). These metals were attributed to different sources: rail tracks, wheels, brakes, and crustal origin. Weak to moderate associations were shown for the analyzed transition metals with PM_2.5-induced cell viability and cellular ROS. Multiple linear regression analysis revealed that Ni, Zn, Mn, Fe, Ti, and Co attributed to cytotoxicity and ROS generation. These findings underscore the importance of commuter exposures and their toxic effects, urging effective mitigating strategies to protect human health.

Photo-oxidation of particle phase iron species dominates the generation of reactive oxygen species in secondary aerosol

This study presents an experimental investigation on the photochemical transformation of iron species in aerosol including dissolution of insoluble iron species into soluble fraction, and soluble ferric oxidation to ferrous form. This process has significantly contributed to the aerosol oxidative potential in generation of reactive oxygen species (ROS). We conducted both laboratory experiment of UV irradiation and real world solar irradiation on large variation of aerosol samples for the characterization of iron speciation in insoluble and soluble fractions to investigate their transformation under photooxidation process. The results showed that the real world solar irradiation significantly increased the soluble Fe(II) fraction, and this is corroborated by laboratory simulation of UV irradiation showing increasing soluble Fe(II) fraction with elongating aging time. The results further exhibited that the dissolution of iron component into soluble fraction was a dominant process, followed by the conversion of soluble ferric to ferrous ions. Further, the study confirmed that the oxidative potential of particulate matter (PM) is attributed dominantly to the abundance of transition metals, i.e. Fe, and the incremental ROS generation after photochemical process is attributed largely to the transformation of solid phase iron species to soluble Fe(II). The results suggest that transition metals, for example by iron in this study, play an important role in secondary aerosol process.

Diurnal trends in redox characteristics of water-soluble and -insoluble PM components

Densely populated cities with a compact urban built environment have concerns over health risks derived from high levels of airborne particulate matter (PM) exposure. Understanding the association between PM and reactive oxygen species (ROS) is an important step towards unravelling the mechanisms behind. This study investigated the role of time-integrated PM sampling on cellular toxicity mechanism on a diurnal scale. The sampling took place in a highly urbanized part of Hong Kong at two contrast roadside and background sites, with simultaneous solid-PM and semi-volatile-PM (SV-PM) collection in both summer and winter seasons. A sampling day consisted three sampling intervals of 6 h each - 04:00-10:00, 12:00-18:00 and 20:00-02:00 h, representing morning rush hours, afternoon and night periods, respectively. Water and organic extracts of PM were prepared, with and without filtration, and exposed to RAW264.7 and A549  cell lines on a dose and time-dependent manner. Solid-PM and SV-PM contribution to total PM_2.5 mass concentration was 9:1, with much higher SV-PM fraction at roadside over urban background (p < 0.001, n = 36). Also, the SV-PM mass concentration increased by 10-20% during 20:00-02:00 h compared to morning and afternoon sampling periods. Organic PM extract was observed to cause 23-29% higher cell death compared to water-soluble PM, which is complemented with increased ROS production in both cell lines. The cellular damage caused by oxidative stress, determined from increased HO-1 and TNF-α expression in RAW264.7 was higher compared to the A549, which demonstrated the greater induction of toxicity from organic PM extract over soluble PM. Similarly, the SV-PM induced greater than 2-fold cellular ROS generation on PM mass basis compared to solid-PM. Lack of phagocytic action in A549 compared to RAW264.7 suggested novel toxicity routes for water-soluble and organic PM that can be expected to occur during human PM inhalation-bronchi-alveolar exposure.

Health effects of particulate matter air pollution in underground railway systems - a critical review of the evidence

BACKGROUND

Exposure to ambient airborne particulate matter is a major risk factor for mortality and morbidity, associated with asthma, lung cancer, heart disease, myocardial infarction, and stroke, and more recently type 2 diabetes, dementia and loss of cognitive function. Less is understood about differential effects of particulate matter from different sources. Underground railways are used by millions of people on a daily basis in many cities. Poor air exchange with the outside environment means that underground railways often have an unusually high concentration of airborne particulate matter, while a high degree of railway-associated mechanical activity produces particulate matter which is physicochemically highly distinct from ambient particulate matter. The implications of this for the health of exposed commuters and employees is unclear.

MAIN BODY

A literature search found 27 publications directly assessing the potential health effects of underground particulate matter, including in vivo exposure studies, in vitro toxicology studies, and studies of particulate matter which might be similar to that found in underground railways. The methodology, findings, and conclusions of these studies were reviewed in depth, along with further publications directly relevant to the initial search results. In vitro studies suggest that underground particulate matter may be more toxic than exposure to ambient/urban particulate matter, especially in terms of endpoints related to reactive oxygen species generation and oxidative stress. This appears to be predominantly a result of the metal-rich nature of underground particulate matter, which is suggestive of increased health risks. However, while there are measureable effects on a variety of endpoints following exposure in vivo, there is a lack of evidence for these effects being clinically significant as may be implied by the in vitro evidence.

CONCLUSION

There is little direct evidence that underground railway particulate matter exposure is more harmful than ambient particulate matter exposure. This may be due to disparities between in vivo exposures and in vitro models, and differences in exposure doses, as well as statistical under powering of in vivo studies of chronic exposure. Future research should focus on outcomes of chronic in vivo exposure, as well as further work to understand mechanisms and potential biomarkers of exposure.

Toxicity of the readily leachable fraction of urban PM2.5 to human lung epithelial cells: Role of soluble metals

Fine airborne particulate matter (PM_2.5) has been repeatedly associated with adverse health effects in humans. The PM_2.5 soluble fraction, and soluble metals in particular, are thought to cause lung damage. Literature data, however, are not consistent and the role of leachable metals is still under debate. In this study, Winter and Summer urban PM_2.5 aqueous extracts, obtained by using a bio-compatible solution and different contact times at 37 °C, were used to investigate cytotoxic effects of PM_2.5 in cultured lung epithelial cells (A549) and the role played by the leachable metals Cu, Fe, Zn, Ni, Pb and Cd. Cell viability and migration, as well as intracellular glutathione, extracellular cysteine, cysteinylglycine and homocysteine concentrations, were evaluated in cells challenged with both PM_2.5 extracts before and after ultrafiltration and artificial metal ion solutions mimicking the metal composition of the genuine extracts. The thiol oxidative potential was also evaluated by an abiotic test. Results demonstrate that PM_2.5 bioactive components were released within minutes of PM_2.5 interaction with the leaching solution. Among these are i) low MW (<3 kDa) solutes inducing oxidative stress and ii) high MW and/or water-insoluble compounds largely contributing to thiol oxidation and to increased homocysteine levels in the cell medium. Cu and/or Ni ions likely contributed to the effects of Summer PM_2.5 extracts. Nonetheless, the strong bio-reactivity of Winter PM_2.5 extracts could not be explained by the presence of the studied metals. A possible role for PM_2.5 water-extractable organic components is discussed.

Metal composition of ambient PM2.5 influences the pulmonary function of schoolchildren: A case study of school located nearby of an electric arc furnace factory

The present study combined air sampling with pulmonary function tests (PFTs) to determine both the extent of air pollution proximal to an electric arc furnace (EAF) and its impact on human health. The mass concentrations of particulate matter with aerodynamic diameters less than 2.5 µm (PM_2.5) in exposure areas were not significantly higher than the samples taken at a control area. However, the concentrations of five metal elements, Cd, Cr, Cu, Ni, and Zn in PM_2.5 were significantly higher in the exposure area than that of the control area. PFTs showed that the average forced vital capacity (FVC) of boys was decreased with decreasing distance from the EAF factory. With normalization of pulmonary function by age, height, and weight, we found that the FVC became more negative with a decrease in distance from the EAF. Lastly, regression analysis was performed to analyze the impact of the concentrations of the five metals in PM_2.5 on the performance of pulmonary function. The results showed that the metals can be ranked from the highest to the lowest in terms of impact on the FVC of boys as follows: Cr, Cd, Ni, Cu, and Zn. This finding is consistent with the ranking of metal toxicity reported in the literature for a rat lung epithelial cell line. The results of this study showed that only measuring PM_2.5 mass concentrations may not provide a full explanation of its toxicity and health effects. The chemical composition of the PM_2.5 can be an important factor that determined the health impact of PM_2.5.

Introductory lecture: atmospheric chemistry in the Anthropocene

The term “Anthropocene” was coined by Professor Paul Crutzen in 2000 to describe an unprecedented era in which anthropogenic activities are impacting planet Earth on a global scale. Greatly increased emissions into the atmosphere, reflecting the advent of the Industrial Revolution, have caused significant changes in both the lower and upper atmosphere. Atmospheric reactions of the anthropogenic emissions and of those with biogenic compounds have significant impacts on human health, visibility, climate and weather. Two activities that have had particularly large impacts on the troposphere are fossil fuel combustion and agriculture, both associated with a burgeoning population. Emissions are also changing due to alterations in land use. This paper describes some of the tropospheric chemistry associated with the Anthropocene, with emphasis on areas having large uncertainties. These include heterogeneous chemistry such as those of oxides of nitrogen and the neonicotinoid pesticides, reactions at liquid interfaces, organic oxidations and particle formation, the role of sulfur compounds in the Anthropocene and biogenic–anthropogenic interactions. A clear and quantitative understanding of the connections between emissions, reactions, deposition and atmospheric composition is central to developing appropriate cost-effective strategies for minimizing the impacts of anthropogenic activities. The evolving nature of emissions in the Anthropocene places atmospheric chemistry at the fulcrum of determining human health and welfare in the future.

Investigation on the mechanism of non-photocatalytically TiO2 -induced reactive oxygen species and its significance on cell cycle and morphology

Titanium dioxide (TiO2 ) nanoparticles are widely used in daily human life, and were reported to elicit biological effects such as oxidative stress either generating reactive oxygen species (ROS) or causing cell necrosis without generating ROS, whose underlying molecular mechanisms are not yet known. In this study, the role of dissolved oxygen in TiO2 catalytic activity in dark environment, and long-term cytotoxic effects of TiO2 exposure were investigated. To determine the effect of dissolved oxygen, the anatase-TiO2 nanoparticle suspension was prepared both in deoxygenated and regular MilliQ water, and a ~ 9-fold higher ROS in regular MilliQ samples was observed compared to deoxygenated samples while in the dark, which suggested dissolved oxygen as the driving agent behind the TiO2 catalytic reaction. On the other hand, the differential cell viability and endogenous ROS activity was demonstrated through a sensitive macrophage-based assay, on a dose- and time-dependent manner. Both the cell number and endogenous ROS activity increased with increase in time till 48 h, followed by a reduction at 72 h exposure period. Long-term exposures to these nanoparticles even at low concentrations were found detrimental to cells, where late apoptosis until 48 h and necrosis at 72 h leading to cell death were noted. Late apoptotic events and cell membrane cytoskeletal actin rearrangement observed were hypothesized to be induced by particle-mediated cellular ROS. This in addition to radical generation ability of TiO2 in the dark will help further in better understanding of the toxicity mechanism in cells beyond ROS generation. Copyright © 2016 John Wiley & Sons, Ltd.

ROS-generating/ARE-activating capacity of metals in roadway particulate matter deposited in urban environment

In this study we investigated the possible causal role for soluble metal species extracted from roadway traffic emissions in promoting particulate matter (PM)-induced reactive oxygen species (ROS) production and antioxidant response element (ARE) promoter activation. To this end, these responses have been evaluated in alveolar macrophage and epithelial lung cells that have been exposed to 'Unfiltered', 'Filtered' and 'Filtered+Chelexed' water extracts of PM samples collected from the roadway urban environments of Thessaloniki, Milan and London. Except for Thessaloniki, our results demonstrate that filtration resulted in a minor decrease in ROS activity of the fine PM fraction, suggesting that ROS activity is attributed mainly to water-soluble PM species. In contrast to ROS, ARE activity was mediated predominantly by the water-soluble component of PM present in both the fine and coarse extracts. Further removal of metals by Chelex treatment from filtered water extracts showed that soluble metal species are the major factors mediating ROS and ARE activities of the soluble fraction, especially in the London PM extracts. Finally, utilizing step-wise multiple-regression analysis, we show that 87% and 78% of the total variance observed in ROS and ARE assays, respectively, is accounted for by changes in soluble metal concentration. Using a statistical analysis we find that As, Zn and Fe best predict the ROS-generating/ARE-activating capacity of the near roadway particulate matter in the pulmonary cells studied. Collectively, our findings imply that soluble metals present in roadside PM are potential drivers of both pro- and anti-oxidative effects of PM in respiratory tract.

Source apportionment and water solubility of metals in size segregated particles in urban environments

Metals in atmospheric particulate matter (PM) have been associated with various adverse health effects. Different factors contributing to the characterization and distribution of atmospheric metals in urban environments lead to uncertainty of the understanding of their impact on public health. However, few studies have provided a comprehensive picture of the spatial and seasonal variability of metal concentration, solubility and size distribution, all of which have important roles in their contribution to health effects. This study presents an experimental investigation on the characteristics of metals in PM2.5 and coarse PM in two seasons from four urban sites in Hong Kong. The PM samples were extracted separately with aqua regia and water, and a total of sixteen elements were analyzed using ICP-MS and ICP-OES to determine the size segregated concentration and solubility of metals. The concentrations of major metals were distributed in similar patterns with the same order of magnitude among different urban sites. Source apportionment using Positive Matrix Factorization (PMF) indicated that three sources namely road dust, vehicular exhaust and ship emission are major contributors to the urban atmospheric metal concentrations in Hong Kong with distinctly different profiles between coarse PM and PM2.5 fractions. The individual metals were assigned to different sources, consistent with literature documentation, except potassium emerging with substantial contribution from vehicle exhaust emission. Literature data from past studies on both local and other cities were compared to the results from the present study to investigate the impact of different emission sources and control policies on metal distribution in urban atmosphere. A large variation of solubility among the metals reflected that the majority of metals in PM2.5 were more soluble than those in coarse PM indicating size dependent chemical states of metals. The data from this study provides a rich dataset of metals in urban atmosphere and can be useful for targeted emission control to mitigate the adverse impact of metallic pollution on public health.

OH-Radical Specific Addition to Glutathione S-Atom at the Air-Water Interface: Relevance to the Redox Balance of the Lung Epithelial Lining Fluid

Antioxidants in epithelial lining fluids (ELF) prevent inhaled air pollutants from reaching lung tissue. This process, however, may upset ELF's redox balance, which is deemed to be expressed by the ratio of the major antioxidant glutathione (GSH) to its putative oxidation product GSSG. Previously, we found that at physiological pH O3(g) rapidly oxidizes GS(2-)(aq) (but not GSH(-)) to GSO3(-) rather than GSSG. Here, we report that in moderately acidic pH ≤ 5 media ·OH(g) oxidizes GSH(-)(aq) to sulfenic GSOH(-), sulfinic GSO2(-), and sulfonic GSO3(-) acids via ·OH specific additions to reduced S-atoms. The remarkable specificity of ·OH on water versus its lack of selectivity in bulk water implicates an unprecedented steering process during [OH···GSH] interfacial encounters. Thus, both O3 and ·OH oxidize GSH to GSOH(-) under most conditions, and since GSOH(-) is reduced back to GSH in vivo by NADPH, redox balance may be in fact signaled by GSH/GSOH ratios.