Solubility of iron from combustion source particles in acidic media linked to iron speciation

Dominant Contribution of Non-dust Primary Emissions and Secondary Processes to Dissolved Aerosol Iron

Solubility largely determines the impacts of aerosol Fe on marine ecosystems and human health. Currently, modeling studies have large uncertainties in aerosol Fe solubility due to inadequate understanding of the sources of dissolved Fe. This work investigated seasonal variations of Fe solubility in coarse and fine aerosols in Qingdao, a coastal city in the Northwest Pacific, and utilized a receptor model for source apportionment of total and dissolved aerosol Fe. Desert dust was found to be the main source of total Fe, contributing 65 and 81% annually to total Fe in coarse and fine particles, respectively; in contrast, dissolved aerosol Fe originated primarily from combustion, industrial, and secondary sources. The annual average contributions to dissolved Fe in coarse and fine particles were 68 and 47% for the secondary source and 32 and 33% for the combustion source, respectively. Aerosol Fe solubility was found to be highest in summer and lowest in spring, showing seasonal patterns similar to those of aerosol acidity. Increase in Fe solubility in atmospheric particles, when compared to desert dust, was mainly caused by secondary processing and combustion emission, and the effect of secondary processes was dictated by aerosol acidity and liquid water content.

Comparison of river and coastal water as potential sources of bioavailable iron

The assimilation of dissolved iron by phytoplankton depends on its chemical speciation and/or oxidation state. In this study river and coastal water was irradiated with a sunlight simulator and monitored for photoproduction of bioavailable reduced iron using a colorimetric method. The 0.01 μΜ steady-state concentration of ferrous ion was detected in river water during irradiation. The apparent quantum yield, an estimate of process efficiency, suggests qualitative differences between organic iron complexes in river and coastal water. The amount of photoproduced bioavailable iron may be of importance in relieving iron stress in potentially toxic diazotrophs in the area affected by the river plume.

Impact of Molecular Chlorine Production from Aerosol Iron Photochemistry on Atmospheric Oxidative Capacity in North China

Elevated levels of atmospheric molecular chlorine (Cl2) have been observed during the daytime in recent field studies in China but could not be explained by the current chlorine chemistry mechanisms in models. Here, we propose a Cl2 formation mechanism initiated by aerosol iron photochemistry to explain daytime Cl2 formation. We implement this mechanism into the GEOS-Chem chemical transport model and investigate its impacts on the atmospheric composition in wintertime North China where high levels of Cl2 as well as aerosol chloride and iron were observed. The new mechanism accounts for more than 90% of surface air Cl2 production in North China and consequently increases the surface air Cl2 abundances by an order of magnitude, improving the model's agreement with observed Cl2. The presence of high Cl2 significantly alters the oxidative capacity of the atmosphere, with a factor of 20-40 increase in the chlorine radical concentration and a 20-40% increase in the hydroxyl radical concentration in regions with high aerosol chloride and iron loadings. This results in an increase in surface air ozone by about 10%. This new Cl2 formation mechanism will improve the model simulation capability for reactive chlorine abundances in the regions with high emissions of chlorine and iron.

Microscopic and spectroscopic analysis of atmospheric iron-containing single particles in Lhasa, Tibet

The Tibetan Plateau, known as the "Third Pole", is currently in a state of perturbation caused by intensified human activity. In this study, 56 samples were obtained at the five sampling sites in typical area of Lhasa city and their physical and chemical properties were investigated by TEM/EDS, STXM, and NEXAFS spectroscopy. After careful examination of 3387 single particles, the results showed that Fe should be one of the most frequent metal elements. The Fe-containing single particles in irregular shape and micrometer size was about 7.8% and might be mainly from local sources. Meanwhile, the Fe was located on the subsurface of single particles and might be existed in the form of iron oxide. Interestingly, the core-shell structure of iron-containing particles were about 38.8% and might be present as single-, dual- or triple-core shell structure and multi-core shell structure with the Fe/Si ratios of 17.5, 10.5, 2.9 and 1.2, respectively. Meanwhile, iron and manganese were found to coexist with identical distributions in the single particles, which might induce a synergistic effect between iron and manganese in catalytic oxidation. Finally, the solid spherical structure of Fe-containing particles without an external layer were about 53.4%. The elements of Fe and Mn were co-existed, and might be presented as iron oxide-manganese oxide-silica composite. Moreover, the ferrous and ferric forms of iron might be co-existed. Such information can be valuable in expanding our understanding of Fe-containing particles in the Tibetan Plateau atmosphere.

Distinct photochemistry of adsorbed and coprecipitated dicarboxylates with ferrihydrite: Implications for iron reductive dissolution and carbon stabilization

Although ligand-promoted photodissolution of ferrihydrite (FH) has long been known for low molecular weight organic acids (LMWOAs), such as oxalate (Oxa) and malonate (Mal), photochemistry of coprecipitated FH with Oxa and Mal remains unknown, despite the importance of these mineral-organic associations in carbon retention has been acknowledged recently. In this study, ferrihydrite-LMWOAs associations (FLAs) were synthesized under circumneutral conditions. Photo-dissolution kinetics of FLAs were compared with those of adsorbed LMWOAs on FH surface and dissolved Fe-LMWOAs complexes through monitoring Fe(II) formation and organic carbon decay. For aqueous Fe(III)-LMWOAs complexes, Fe(II) yield was controlled by the initial concentration of LMWOAs and nature of photochemically generated carbon-centered radicals. Inner-sphere mononuclear bidentate (MB) configuration dominated while LMWOAs were adsorbed on the FH surface. MB complex of FH-Oxa was more photoreactive, leading to the rapid depletion of Oxa. Oxa can be readsorbed but in the form of binuclear bidentate and outer-sphere complexation, with much lower photoreactivity. While LMWOAs was coprecipitated with FH, the combination mode of LMWOAs with FH includes surface adsorption with a mononuclear bidentate structure and internal physical inclusion. Higher content of LMWOAs in the FLAs promoted the photo-production of Fe(II) as compared to pure FH, while it was not the case for FLAs containing moderate amounts of LMWOAs. The distinct photochemistry of adsorbed and coprecipitated Fe-LMWOAs complexes is attributed to ligand availability and configuration patterns of LMWOAs on the surface or entrapped in the interior structure. The present findings have significant implications for understanding the photochemical redox cycling of iron across the interface of Fe-organic mineral associates.

Quantifying anthropogenic emission of iron in marine aerosol in the Northwest Pacific with shipborne online measurements

Anthropogenic emissions are recognized as significant contributors to atmospheric soluble iron (Fe) in recent years, which may affect marine primary productivity, especially in Fe-limited areas. However, the contribution of different emission sources to Fe in marine aerosol has been primarily estimated by modeling approaches. Quantifying anthropogenic Fe based on field measurements remains a great challenge. In this study, online multi-element measurements and Positive Matrix Factorization (PMF) were combined for the first time to quantify sources of atmospheric Fe and soluble Fe in the Northwest Pacific during a cruise in spring 2015. Fe concentration in 624 atmospheric PM2.5 samples measured online was 74.58 ± 90.87 ng/m3. The PMF results showed anthropogenic activities, including industrial coal combustion, biomass burning, and maritime transport, were important in this region, contributing 31.4 % of atmospheric Fe on average. In addition, anthropogenic Fe concentration resolved by PMF was comparable to the simulation results of the CMAQ (Community Multiscale Air Quality) and GEOS-Chem (Goddard Earth Observing System-Chemical transport) models, with better correlation to CMAQ (r = 0.76) than GEOS-Chem (r = 0.26). This study developed a new method to estimate atmospheric soluble Fe, which integrates Fe source apportionment results and Fe solubility from different sources. Soluble Fe concentration was estimated as 3.93 ± 5.14 ng/m3, of which 87.0 % was attributed to anthropogenic emissions. Notably, ship emission alone contributed 27.5 % of soluble Fe, though its contribution to total Fe was only 2.2 %. Finally, the total deposition fluxes of atmospheric Fe (37.11 ± 38.43 μg/m2/day) and soluble Fe (1.85 ± 2.13 μg/m2/day) were estimated. This study developed a new methodology for quantifying contribution of anthropogenic emissions to Fe in marine aerosol, which could greatly help the assessment of impacts of human activities on marine environment.

Impacts of coexisting mineral on crystallinity and stability of Fe(II) oxidation products: Implications for neutralization treatment of acid mine drainage

The neutralization treatment of acid mine drainage involves the oxidation of Fe(II), but little is known about the effects of co-existing minerals on the oxidation and hydrolysis of Fe(II) to iron oxides. Here we investigated the transformation of fresh and heated Fe(II) oxidation coprecipitates, which were synthesized in the presence and the absence of five co-existing minerals (montmorillonite, kaolin, quartz (SiO₂)_, aluminium oxide (Al₂O₃) and calcium carbonate (CaCO₃)). In the FeSO₄ system with montmorillonite or kaolin, the formation of lepidocrocite was inhibited with the increase of clay mineral contents. In the same system, heated coprecipitates of montmorillonite were mainly comprised of amorphous ferrihydrite and its transformation was retarded by the excess montmorillonite. In the FeCl₂ system with SiO₂, Al₂O₃ or CaCO₃, akaganeite formation was inhibited with the increase in the corresponding mineral contents. In the same system, goethite formation was blocked by either CaCO₃ or Al₂O₃ and the growth of lepidocrocite was inhibited by CaCO₃ or SiO₂. However, magnetite formation was enhanced by addition of CaCO₃. These findings are important for predicting products of abiotic Fe(II) oxidation during the neutralization of acid mine drainage and for better understanding the transformation of amorphous iron oxides in the complicated environmental matrix.

Water-soluble iron in PM2.5 in winter over six Chinese megacities: Distributions, sources, and environmental implications

Water-soluble iron (ws-Fe) in PM_2.5 plays a crucial role in biogeochemical cycles and atmospheric chemical processes. The anthropogenic sources of ws-Fe have attracted considerable attention owing to its high solubility. However, few studies have investigated the content of PM_2.5 ws-Fe in the urban environment. In the present study, we characterized the spatial distributions of ws-Fe in six Chinese megacities in the winter of 2019. Furthermore, we investigated the speciation of PM_2.5 ws-Fe (ws-Fe(II) and ws-Fe(III)), potential sources of ws-Fe, and association between ws-Fe and particle-bound reactive oxygen species (ROS). Higher ws-Fe concentrations were observed in northern cities (Harbin, Beijing, and Xi'an) than in southern cities (Chengdu, Wuhan, and Guangzhou). Moreover, atmospheric ws-Fe concentrations in urban China were several folds higher than those in urban areas of the United States and several orders of magnitude higher than those in remote oceans, indicating that China is a key contributor to global atmospheric ws-Fe. The dominant form of ws-Fe was ws-Fe(III) in Beijing, whereas ws-Fe(II) was more abundant in the other five cities. The concentrations of ws-Fe and ws-Fe(II) concentrations increased with increasing PM_2.5 levels in all the six cities, however, we did not observe any consistent pattern of ws-Fe(III) concentration. Biomass burning was a dominant source of ws-Fe in all cities except Beijing. A strong positive correlation was observed between particle-bound ROS content and ws-Fe; this finding is consistent with those of previous studies indicating that ws-Fe in PM_2.5 notably influences atmospheric chemical processes and human health.

Impact of particle sizes on health risks and source-specific health risks for heavy metals in road dust

To analyze the impact of particle sizes on sources and related health risks for heavy metals, road dust samples in Beijing were collected and sifted into five particle sizes. The positive matrix factorization (PMF), human health risk assessment model (HHRA), and Monte Carlo simulation were used in the health risk assessment and source apportionment. Results showed that mass of particles < 74 μm occupied about 50% of the total particles, while only 8.48% of the particles were > 500 μm. Mass distribution and concentrations of heavy metals in each particle size changed in temporal. Over 85.00% of carcinogenic risks (CR) were from particles <74 μm, whereas CR from particles >250 μm were ignorable. Sources for health risks in each particle size were traffic exhaust, fuel combustion, construction, and use of pesticides and fertilizers. Proportions of sources to CR differed among particle sizes. Traffic exhaust and fuel combustion contributed over 90% to CR in particles <74 μm, whereas construction contributed the highest (31.68-54.14%) among all sources in particles 74-250 μm. Furthermore, the difference between health risks based on sifted road dust and that based on unsifted road dust was quantitatively analyzed. Source-specific health risk apportionment based on unsifted road dust was not presentative to all particle sizes, and true value of health risks could be over 2.5 times of the estimated value based on unsifted road dust, emphasized the importance of sifting of road dust.

Mass fractions, solubility, speciation and isotopic compositions of iron in coal and municipal waste fly ash

Deposition of anthropogenic aerosols may contribute significantly to dissolved Fe in the open ocean, affecting marine primary production and biogeochemical cycles; however, fractional solubility of Fe is not well understood for anthropogenic aerosols. This work investigated mass fractions, solubility, speciation and isotopic compositions of Fe in coal and municipal waste fly ash. Compared to desert dust (3.1 ± 1.1%), the average mass fraction of Fe was higher in coal fly ash (6.2 ± 2.7%) and lower in municipal waste fly ash (2.6 ± 0.4%), and the average Fe/Al ratios were rather similar for the three types of particles. Municipal waste fly ash showed highest Fe solubility (1.98 ± 0.43%) in acetate buffer (pH: 4.3), followed by desert dust (0.43 ± 0.30%) and coal fly ash (0.24 ± 0.28%), suggesting that not all the anthropogenic aerosols showed higher Fe solubility than desert dust. For the samples examined in our work, amorphous Fe appeared to be an important controlling factor for Fe solubility, which was not correlated with particle size or BET surface area. Compared to desert dust (-0.05‰ to 0.21‰), coal and municipal waste fly ash showed similar or even higher δ⁵⁶Fe values for total Fe (range: 0.05‰ to 0.75‰), implying that the presence of coal or municipal waste fly ash may not be able to explain significantly smaller δ⁵⁶Fe values reported for total Fe in ambient aerosols affected by anthropogenic sources.

Aerosol iron speciation and seasonal variation of iron oxidation state over the western Antarctic Peninsula

The iron (Fe) speciation and oxidation state have been considered critical factors affecting Fe solubility in the atmosphere and bioavailability in the surface ocean. In this study, elemental composition and Fe speciation in aerosol samples collected at the Palmer Station in the West Antarctic Peninsula were determined using synchrotron-based X-ray fluorescence (XRF) and X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The elemental composition of coarse-mode (>1 μm) Fe-containing particles suggests that the region's crustal emission is the primary source of aerosol Fe. The Fe minerals in these aerosol particles were predominantly hematite and biotite, but minor fractions of pyrite and ilmenite were observed as well. The Fe oxidation state showed an evident seasonal variation. The Fe(II) content accounted for 71% of the total Fe in the austral summer, while this fraction dropped to 60% in the austral winter. Multivariate linear models involving meteorological parameters suggested that the wind speed, relative humidity, and solar irradiance were the factors that significantly controlled the percentage of Fe(II) in the austral summer. On the contrary, no relationship was found between these factors and the Fe(II) percentage in the austral winter, suggesting that atmospheric photoreduction and regional dust emission were limited. Moreover, the snow depth was significantly (p < 0.05) correlated with the aerosol Fe concentration, confirming the limiting effect of snow/ice cover on the regional dust emission. Given that the Antarctic Peninsula has experienced rapid warming during recent decades, the ice-free areas in the Antarctic Peninsula may act as potential dust sources.

Variations in concentration and solubility of iron in atmospheric fine particles during the COVID-19 pandemic: An example from China

Iron (Fe) in the atmosphere can affect atmospheric chemical processes and human health. When deposited into oceans, it can further influence phytoplankton growth. These roles of Fe fundamentally depend on its concentration and solubility. However, the sources of aerosol Fe and controlling factors of Fe solubility in megacities remain poorly understood. The outbreak of the COVID-19 pandemic causes large changes in human activities, which provides a unique opportunity to answer these key issues. Field observations were conducted before, during, and after the COVID-19 lockdown in Hangzhou, China. Our results show that in the COVID-19 lockdown stage, the concentrations of total Fe (FeT, 75.0 ng m-3) and soluble Fe (FeS, 5.1 ng m-3) in PM2.5 decreased by 78% and 62%, respectively, compared with those (FeT 344.7 ng m-3, FeS 13.5 ng m-3) in the pre-lockdown stage. The sharp reduction (81%) in on-road vehicles was most responsible for the aerosol Fe decrease. Surprisingly, the Fe solubility increased by a factor of 1.9, from 4.2% in the pre-lockdown stage to 7.8% in the COVID-19 lockdown stage. We found that the atmospheric oxidizing capacity was enhanced after lockdown restrictions were implemented, which promoted the formation of more acidic species and further enhanced the dissolution of aerosol Fe.

Trends in particle matter and its elemental composition in Santiago de Chile, 2011 - 2018

Daily fine (PM_2.5) and coarse (PM_10-2.5) particle matter (PM) samples collected at Parque O'Higgins station in downtown Santiago de Chile have been studied to find the trends in concentration from 1998 to 2018. Elemental concentration was obtained using X-ray fluorescence (XRF). Regression models from previous studies indicate that the PM_2.5 and PM_10-2.5 fractions have had a continuous decrease since 1988 mostly due to several policy control measures carried out over several decades. PM_2.5 has decreased from 68.3 in 1988 to 27.6 μg/m³ in 2018 (60.4%). However, if only the last 8 years are considered (2011-2018), a leveling off can be observed in PM_10-2.5 and PM_2.5, which points to a change in the tendency. Cluster analysis of the elements in the fine and coarse fractions were identified to evaluate trends in the contributing sources. In the fine fraction, the mass contribution of crustal elements (Si, Al, Ca, and Fe) has remained stable in the last 8 years, and mass contribution of elements (Pb, Br, and Cl) associated to anthropogenic sources (traffic, wood burning) has also remained stable in the same period. For the coarse fraction, the contribution of one group of elements associated to crustal or anthropogenic sources has remained stable, and another group has decreased in the last 8 years. The leveling off can be ascribed to decreased rainfall during the last 8 years that have promoted soil dryness and resuspension of dust facilitated by wind or vehicular traffic. Mean temperatures have increased in the last 30 years, but have not contributed directly to the leveling of the concentration.Implications: Regression models indicate that the PM_2.5 (fine) and PM_10-2.5 (coarse) fractions at Parque O'Higgins station in Santiago de Chile have had a continuous decrease since 1988 mostly due to several policy control measures carried out over several decades. However, in the last 8 years (2011-2018), a leveling off can be observed in PM_10-2.5 and PM_2.5. X-ray fluorescence (XRF) analysis was performed in the fine fractions indicating that the mass contribution of crustal elements (Ca, Al, Si, Fe) to the fine fraction has remained stable. This phenomenon can be ascribed to decreased rainfall during the last 8 years that have promoted soil dryness and resuspension of dust facilitated by wind or vehicular traffic. The crustal elements in the coarse fraction have also remained stable.

Atmospheric outflow of anthropogenic iron and its deposition to China adjacent seas

Atmospheric deposition of iron (Fe) can increase marine primary productivity, consequently affect ocean biogeochemical cycles and climate change. In this study, we develop an adaptor to generate anthropogenic Fe emission inventories for China in 2012 and 2016 via anthropogenic PM_2.5 emissions from Multi-resolution Emission Inventory for China (MEIC) using local source-specific mass fractions of Fe in PM_2.5. Using the generated emission inventories, we simulated Fe concentrations as well as dry deposition fluxes to China marginal seas using a WRF-CMAQ model during four campaign periods. The simulated Fe concentrations are in good agreement with observations except for those in presence of severe dust-intrusion events (NMB -13% ~ -27%), indicating a reasonably good performance of the generated Fe emissions and leaving the large underestimation of Fe concentrations mainly due to nature dust emissions. Simulated Fe concentrations over China marginal seas are in the range of 62-6.5 × 10² ng m^-3, providing 2.0-12.5 μg m^-2 d^-1 to the seas during the study periods. We also found that inputs of total Fe in PM_2.5 to the seas in presence of dust-intrusion events are 3 and 13 times larger than those in presence of haze events or on less polluted days. Due to lower Fe solubility in nature mineral aerosols than in anthropogenic aerosols, dry deposition fluxes of bioavailable Fe on haze days almost double that in dust days. The total anthropogenic emissions of Fe over China in 2012 and 2016 are estimated as 5.5 × 10² Gg and 3.3 × 10² Gg, respectively. Iron and steel industry are the dominant sources of Fe, accounting for 59-63% of the total anthropogenic Fe emissions. Geotropically, stronger emissions per area were distributed in eastern China, e.g., 2.3 to 15.4 ng m^-2 s^-1 in eastern China versus <0.4 ng m^-2 s^-1 in western China.

Iron solubility in fine particles associated with secondary acidic aerosols in east China

Soluble iron (Fe_S) in aerosols contributes to free oxygen radical generation with implications for human health, and potentially catalyzes sulfur dioxide oxidation. It is also an important external source of micronutrients for ocean ecosystems. However, factors controlling Fe_S concentration and its contribution to total iron (Fe_T) in aerosols remain poorly understand. Here, Fe_S and Fe_T in PM_2.5 was studied at four urban sites in eastern China from 21 to 31 December, 2017. Average Fe_T (869-1490 ng m^-3) and Fe_S (24-68 ng m^-3) concentrations were higher in northern than southern China cities, but Fe solubility (%Fe_S, 2.7-5.0%) showed no spatial pattern. Correlation analyses suggested %Fe_S was strongly correlated with Fe_S and PM_2.5 instead of Fe_T concentrations. Individual particle observations confirmed that more than 65% of nano-sized Fe-containing particles were internally mixed with sulfates and nitrates. Furthermore, there was a high correlation between sulfates or nitrates/Fe_T molar ratio and %Fe_S. We also found that the sulfates/nitrates had weaker effects on %Fe_S at RH < 50% than at RH > 50%, suggesting RH as indirect factor can influence %Fe_S in PM_2.5. These results suggest an important role of chemical processing in enhancing %Fe_S in the polluted atmosphere.

Endogenous doesn't always mean innocuous: a scoping review of iron toxicity by inhalation

Ambient air pollution is a leading risk factor for the global burden of disease. One possible pathway of particulate matter (PM)-induced toxicity is through iron (Fe), the most abundant metal in the atmosphere. The aim of the review was to consider the complexity of Fe-mediated toxicity following inhalation exposure focusing on the chemical and surface reactivity of Fe as a transition metal and possible pathways of toxicity via reactive oxygen species (ROS) generation as well as considerations of size, morphology, and source of PM. A broad term search of 4 databases identified 2189 journal articles and reports examining exposure to Fe via inhalation in the past 10 years. These were sequentially analyzed by title, abstract and full-text to identify 87 articles publishing results on the toxicity of Fe-containing PM by inhalation or instillation to the respiratory system. The remaining 87 papers were examined to summarize research dealing with in vitro, in vivo and epidemiological studies involving PM containing Fe or iron oxide following inhalation or instillation. The major findings from these investigations are summarized and tabulated. Epidemiological studies showed that exposure to Fe oxide is correlated with an increased incidence of cancer, cardiovascular diseases, and several respiratory diseases. Iron PM was found to induce inflammatory effects in vitro and in vivo and to translocate to remote locations including the brain following inhalation. A potential pathway for the PM-containing Fe-mediated toxicity by inhalation is via the generation of ROS which leads to lipid peroxidation and DNA and protein oxidation. Our recommendations include an expansion of epidemiological, in vivo and in vitro studies, integrating research improvements outlined in this review, such as the method of particle preparation, cell line type, and animal model, to enhance our understanding of the complex biological interactions of these particles.

Heterogeneous reaction of NO2 with hematite, goethite and magnetite: Implications for nitrate formation and iron solubility enhancement

Atmospheric processing may significantly increase solubility of iron in mineral dust, but the effects of heterogeneous reactions on iron solubility have been poorly understood. In this work, we investigated heterogeneous reaction of NO₂ (15 ± 1 and 2.5 ± 0.1 ppmv, equal to ∼3.7 × 10¹⁴ and ∼6.2 × 10¹³ molecule cm^-3) with hematite, magnetite and goethite at different relative humidities (RH, 0-90%), and changes in particulate nitrate and soluble iron due to heterogeneous reaction with NO₂ were quantified as a function of time (up to 24 h). After reaction with 2.5 ± 0.1 ppmv NO₂ for 24 h (or less time), hematite and magnetite were fully saturated, while goethite was only partly deactivated. Nitrate yield was largest for goethite, and the mass ratio of formed nitrate to unreacted mineral only reached ∼1% or less after 24 h reaction. All the three minerals showed low reactivities towards NO₂, and the average reactive uptake coefficients of NO₂ in the first 3 h were found to be < 5 × 10^-8. In addition, the increase in iron solubility was found to be small and in some cases even insignificant for the three minerals after heterogeneous reaction with NO₂ for 24 h. Overall, the impacts of heterogeneous reaction of NO₂ with hematite, magnetite and goethite on nitrate aerosol formation and iron solubility could be very limited.

Atmospheric particulate matters in an Indian urban area: Health implications from potentially hazardous elements, cytotoxicity, and genotoxicity studies

The nature of the atmospheric particulate matters (PMs) varies depending on their sizes and their origin from different activities in the background environment. These PMs are associated with potentially hazardous elements (PHEs) such as organic compounds (e.g. Polyaromatic Hydrocarbons) that can be harmful to health. The main objective of this work is the identification and investigation of the toxicological aspects of PHEs in PMs during pre-monsoon and post-monsoon season in an urban area of Northeast region (NER) of India. In the course of the study, the 24 -hs average concentrations of PMs were detected to be more than two-times higher than the Indian standard limit (NAAQ, category) which indicates poor air quality in both the seasons around the sampling sites. This study demonstrates that the concentrations of PM-bound PAHs are mutagenic and that the Excess Cancer Risks exceed the USEPA standard limits. PMs cause cytotoxicity and can also induce genotoxicity to human health analyzed by cell culture and gel electrophoresis. This study helps to promote research to evaluate the PMs bound PHEs toxicity in diverse human cell lines and also their relationship with climatic factors as well as quantitative source apportionment for mitigation purposes.

Pyrogenic iron: The missing link to high iron solubility in aerosols

Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity.

Efficient removal of several estrogens in water by Fe-hydrochar composite and related interactive effect mechanism of H2O2 and iron with persistent free radicals from hydrochar of pinewood

Recently, hydrochar (HC) with existed persistent free radicals (PFRs) has attracted researches' attention for the potential application in heterogeneous Fenton-like reactions, but studies on the interactive effects of H₂O₂, iron, and HC in removal of organic pollutants are still limited. In this paper, magnetic iron (hydr)oxides immobilized hydrochar composite (Fe/HC) derived from hydrothermal carbon (HTC) of pinewood were synthesized and characterized. The interactive effects of H₂O₂, iron, and HC in the removal of several estrogens were systematically investigated to understand the removal performance and related mechanism, especially at a pH range close to natural water environment. Batch experiments results showed that estrogens could be efficiently removed over Fe/HC material under a wide pH range of 4-9. Based on the analysis of electron spin resonance, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and electrochemical impedance spectroscopy, mechanism study indicated that the carbon-centered PFRs on the surface of hydrochar can act as electron donors, and transfer the electrons on adsorbed O₂ to generate O₂^- rapidly, while the addition of H₂O₂ enhanced the transmission ability of electron to produce OH_(ads) on the material surface. The iron and hydrochar components contributed to the desirable removal of estrogens via the synergistic effect between catalysis and adsorption. This study provides a promising application for the use of Fe/HC materials on remediation of pollution with trace estrogens in water environment.

Primary Particulate Matter Emitted from Heavy Fuel and Diesel Oil Combustion in a Typical Container Ship: Characteristics and Toxicity

Container ships have been widely recognized as an important emission source within maritime transport. Heavy fuel oil (HFO) and diesel oil (DO) are the two most commonly used fuels. This study reports the characteristics and toxicities of particulate matter (PM) emissions from HFO and DO combustion in a typical container ship. The PM number size distribution possesses a bimodal structure with peaks at ∼20 nm and ∼100 nm. The PM_2.5 emission factors (EFs) are 3.15 ± 0.39 and 0.92 ± 0.02 g/kg fuel for HFO and DO, respectively. The benzo[a]pyrene equivalent carcinogenic potency (BaP_eq) of 16 polycyclic aromatic hydrocarbons contained in HFO and DO PM_2.5 is approximately 0.81 ± 0.10 and 0.12 ± 0.04 mg/kg fuel, respectively. BaP_eq concentration shows an increasing tendency with decreased PM size. The reactive oxygen species activity and cytotoxicity of HFO PM_2.5 samples are ∼2.1 and ∼2.5 times higher than those of DO PM_2.5 samples, respectively. These health risks are both significantly attributed to the BaP_eq content in PM_2.5 with correlations of 0.86-0.92. Furthermore, the examined biological effects are much greater than those of atmospheric PM_2.5 collected in Shanghai. Our results imply that better fuel quality is important for improving air quality and reducing health risks.

Characterization and acid-mobilization study for typical iron-bearing clay mineral

In this study, iron speciation in five standard clay samples was characterized. Iron mobilization from these clays was then measured in acidic media. For comparison, a commercially available Arizona test dust (ATD) was also observed. The results showed that the free-Fe contents of clays were commonly lower than that of dust aerosols. The components of clays were dominant by the structural Fe held in the aluminosilicate lattice. The iron solubility of the clays were in the order of KGa-2 > SWy-2 > CCa-2 > IMt-2 > NAu-2. Based upon the Mössbauer spectrum and transmission electron microscopy (TEM) analysis, the Fe(II) fraction and the Fe/Si ratio of clay particles changed after dissolution, suggesting the total Fe solubility depended on the Fe atom states existing within the aluminosilicate lattice. The Fe in KGa-2 and SWy-2 was most likely substituted for alkaline elements as the interlayer ions held by ionic bonds in the aluminosilicate, which are more liable to dissolution. However, the Fe in NAu-2 was more likely to be bound by strong covalent bonds in aluminosilicate mineral, which is less soluble. The much highly soluble Fe in ATD was not only linked to the dissolution of an appreciable fraction of Fe(II), but also could be attributed to the fact that the Fe bonds in the clay fraction of ATD were mainly present as ionic bonds. The TEM images showed that reacted clay particles displayed less aggregate particles, with nanoparticle aggregates and the Fe/S-rich tiny particles attached to the remains.

Radiative forcing by light-absorbing aerosols of pyrogenetic iron oxides

Iron (Fe) oxides in aerosols are known to absorb sun light and heat the atmosphere. However, the radiative forcing (RF) of light-absorbing aerosols of pyrogenetic Fe oxides is ignored in climate models. For the first time, we use a global chemical transport model and a radiative transfer model to estimate the RF by light-absorbing aerosols of pyrogenetic Fe oxides. The model results suggest that strongly absorbing Fe oxides (magnetite) contribute a RF that is about 10% of the RF due to black carbon (BC) over East Asia. The seasonal average of the RF due to dark Fe-rich mineral particles over East Asia (0.4–1.0 W m⁻²) is comparable to that over major biomass burning regions. This additional warming effect is amplified over polluted regions where the iron and steel industries have been recently developed. These findings may have important implications for the projection of the climate change, due to the rapid growth in energy consumption of the heavy industry in newly developing countries.

The variability in iron speciation in size fractionated residual oil fly ash particulate matter (ROFA PM)

Ambient particulate matter (PM) containing iron can catalyze Fenton reaction leading to the production of reactive oxygen species in cells. It can also catalyze atmospheric redox reaction. These reactions are governed by the physicochemical characteristics of iron in ambient PM. As a surrogate for ambient PM, we prepared residual oil fly ash PM (ROFA PM) in a practical fire tube boiler firing residual oils with varying sulfur and ash contents. The ROFA particles were resolved into fine PM or PM2.5 (aerodynamic diameter (AD)<2.5μm) and coarse PM or PM2.5+ (AD between 2.5μm and 50μm). The iron speciation in PM2.5+ was ascertained using X-ray absorption spectroscopy and leaching method while that in PM2.5 was reported earlier. The results of both studies are compared to get an insight into the variability in the iron speciation in different size fractions. The results show the predominance of ferric sulfate, with a minor spinal ferrite in both PM (i.e. ZnxNi1-xFe2O4 in PM2.5, ZnFe2O4 in PM2.5+). The iron solubility in ROFA PM depends on its speciation, mode of incorporation of iron into particle's carbonaceous matrix, the grade and composition of oils, and pH of the medium. The soluble fraction of iron in PM is critical in assessing its interaction with the biological systems and its toxic potential.

Influence of anthropogenic aerosol deposition on the relationship between oceanic productivity and warming

Satellite data and models suggest that oceanic productivity is reduced in response to less nutrient supply under warming. In contrast, anthropogenic aerosols provide nutrients and exert a fertilizing effect, but its contribution to evolution of oceanic productivity is unknown. We simulate the response of oceanic biogeochemistry to anthropogenic aerosols deposition under varying climate from 1850 to 2010. We find a positive response of observed chlorophyll to deposition of anthropogenic aerosols. Our results suggest that anthropogenic aerosols reduce the sensitivity of oceanic productivity to warming from -15.2 ± 1.8 to -13.3 ± 1.6 Pg C yr^-1 °C^-1 in global stratified oceans during 1948-2007. The reducing percentage over the North Atlantic, North Pacific, and Indian Oceans reaches 40, 24, and 25%, respectively. We hypothesize that inevitable reduction of aerosol emissions in response to higher air quality standards in the future might accelerate the decline of oceanic productivity per unit warming.

Fractional iron solubility of aerosol particles enhanced by biomass burning and ship emission in Shanghai, East China

In terms of understanding Fe mobilization from aerosol particles in East China, the PM2.5 particles were collected in spring at Shanghai. Combined with the backtrajectory analysis, the PM2.5/PM10 and Ca/Al ratios, a serious dust-storm episode (DSE) during the sampling was identified. The single-particle analysis showed that the major iron-bearing class is the aluminosilicate dust during DSE, while the Fe-bearing aerosols are dominated by coal fly ash, followed by a minority of iron oxides during the non-dust storm days (NDS). Chemical analyses of samples showed that the fractional Fe solubility (%FeS) is much higher during NDS than that during DSE, and a strong inverse relationship of R(2)=0.967 between %FeS and total atmospheric iron loading were found, suggested that total Fe (FeT) is not controlling soluble Fe (FeS) during the sampling. Furthermore, no relationship between FeS and any of acidic species was established, suggesting that acidic process on aerosol surfaces are not involved in the trend of iron solubility. It was thus proposed that the source-dependent composition of aerosol particles is a primary determinant for %FeS. Specially, the Al/Fe ratio is poorly correlated (R(2)=0.113) with %FeS, while the apparent relationship between %FeS and the calculated KBB(+)/Fe ratio (R(2)=0.888) and the V/Fe ratio (R(2)=0.736) were observed, reflecting that %FeS could be controlled by both biomass burning and oil ash from ship emission, rather than mineral particles and coal fly ash, although the latter two are the main contributors to the atmospheric Fe loading during the sampling. Such information can be useful improving our understanding on iron solubility on East China, which may further correlate with iron bioavailability to the ocean, as well as human health effects associated with exposure to fine Fe-rich particles in densely populated metropolis in China.

Iron dissolution of dust source materials during simulated acidic processing: the effect of sulfuric, acetic, and oxalic acids

Atmospheric organic acids potentially display different capacities in iron (Fe) mobilization from atmospheric dust compared with inorganic acids, but few measurements have been made on this comparison. We report here a laboratory investigation of Fe mobilization of coal fly ash, a representative Fe-containing anthropogenic aerosol, and Arizona test dust, a reference source material for mineral dust, in pH 2 sulfuric acid, acetic acid, and oxalic acid, respectively. The effects of pH and solar radiation on Fe dissolution have also been explored. The relative capacities of these three acids in Fe dissolution are in the order of oxalic acid > sulfuric acid > acetic acid. Oxalate forms mononuclear bidentate ligand with surface Fe and promotes Fe dissolution to the greatest extent. Photolysis of Fe-oxalate complexes further enhances Fe dissolution with the concomitant degradation of oxalate. These results suggest that ligand-promoted dissolution of Fe may play a more significant role in mobilizing Fe from atmospheric dust compared with proton-assisted processing. The role of atmospheric organic acids should be taken into account in global-biogeochemical modeling to better access dissolved atmospheric Fe deposition flux at the ocean surface.

Effects of Eyjafjallajökull volcanic ash on innate immune system responses and bacterial growth in vitro

BACKGROUND

On 20 March 2010, the Icelandic volcano Eyjafjallajökull erupted for the first time in 190 years. Despite many epidemiological reports showing effects of volcanic ash on the respiratory system, there are limited data evaluating cellular mechanisms involved in the response to ash. Epidemiological studies have observed an increase in respiratory infections in subjects and populations exposed to volcanic eruptions.

METHODS

We physicochemically characterized volcanic ash, finding various sizes of particles, as well as the presence of several transition metals, including iron. We examined the effect of Eyjafjallajökull ash on primary rat alveolar epithelial cells and human airway epithelial cells (20-100 µg/cm(2)), primary rat and human alveolar macrophages (5-20 µg/cm(2)), and Pseudomonas aeruginosa (PAO1) growth (3 µg/104 bacteria).

RESULTS

Volcanic ash had minimal effect on alveolar and airway epithelial cell integrity. In alveolar macrophages, volcanic ash disrupted pathogen-killing and inflammatory responses. In in vitro bacterial growth models, volcanic ash increased bacterial replication and decreased bacterial killing by antimicrobial peptides.

CONCLUSIONS

These results provide potential biological plausibility for epidemiological data that show an association between air pollution exposure and the development of respiratory infections. These data suggest that volcanic ash exposure, while not seriously compromising lung cell function, may be able to impair innate immunity responses in exposed individuals.