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

Dry deposition fluxes and inhalation risks of toxic elements in total suspended particles in the Bohai Rim region: Long-term trends and potential sources

Long-term changes in dry deposition fluxes (DDF) and health risks for toxic elements (TE) in total suspended particles (TSP) in the Bohai Rim region are important for assessing control effects of pollution sources. Thus, we investigated the trends in DDF and concentrations for TSP and TE and health risks of TE in eight cities in the region from 2011-2020. TSP concentration and DDF showed general downward trends. Compared to the before Clear Air Action Plan (BCAAP, 2011-2012) period, concentration and DDF of TE over the Clear Air Action Plan (CAAP, 2013-2017) period substantially decreased, with the highest decrease rates in Zn, Cd, and Cr. During the study period, non-carcinogenic (HI) and total carcinogenic (TCR) risks for children and adults were 0.09 and 0.04, and 1.54 × 10-5 and 2.65 × 10-5, respectively, with Cr6+ and As being dominant contributors. Compared to the BCAAP period, HI and TCR over the CAAP period decreased by 36.8 % and 32.4 %, respectively. However, their risks increased over the Blue Sky Protection Campaign (BSPC, 2018-2020) period. Potential source contribution function suggested substantial changes in potential risk areas over different control periods, with the BSPC primarily being on land and the Yellow Sea.

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.

Chemical characteristics, distribution patterns, and source apportionment of particulate elements and inorganic ions in snowpack in Harbin, China

Snowpack, which serves as a natural archive of atmospheric deposition of multiple pollutants, is a practical environmental media that can be used for assessing atmospheric records and input of the pollutants to the surface environments and ecosystems. A total of 29 snowpack samples were collected at 20 sampling sites covering three different functional areas of a major city (Harbin) in Northeast China. Two samples at the "snow layer" and one or two samples at the "particulate layer" were collected at each sampling site in the industrial areas characterized by multi-layer snowpack, and only one sample at the "snow layer" was collected at each sampling site in the cultural and recreational as well as agricultural areas. The snow contents of 31 elements (Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Pb) and six major water-soluble inorganic ions (WSIIs, NH4+, K+, Ca2+, NO2-, NO3-, and SO42-) were analyzed. The total mass of the measured elements is dominated (95.8%-99.2%) by crustal elements. Heavy metals only account for 0.77%-4.07% of the total mass of the elements, but are occasionally close to or even above the standard limit in the "Environmental Quality Standards for Surface Water" of China (GB3838-2002). SO42- and Ca2+ are the main anion and cation, accounting for 34.9%-81.1% and 1.43%-29.9%, respectively, of the measured total ions. Total atmospheric deposition of crustal elements and heavy metals is dominated by wet deposition in areas near the petrochemical plant and by dry deposition in areas near the cement plant. Coal combustion, industrial emissions, and traffic-related activities lead to the enrichment of heavy metals in the snowpacks of urban and suburban areas, while coal combustion and biomass burning contribute to pollution in rural areas. The cities and regions situated in the western, northwestern, northern, and northeastern directions from Harbin are potential source regions of these pollutant species.

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.

Aerosol Oxidative Potential in the Greater Los Angeles Area: Source Apportionment and Associations with Socioeconomic Position

Oxidative potential (OP) has been proposed as a possible integrated metric for particles smaller than 2.5 μm in diameter (PM_2.5) to evaluate adverse health outcomes associated with particulate air pollution exposure. Here, we investigate how OP depends on sources and chemical composition and how OP varies by land use type and neighborhood socioeconomic position in the Los Angeles area. We measured OH formation (OP^OH), dithiothreitol loss (OP^DTT), black carbon, and 52 metals and elements for 54 total PM_2.5 samples collected in September 2019 and February 2020. The Positive Matrix Factorization source apportionment model identified four sources contributing to volume-normalized OP^OH: vehicular exhaust, brake and tire wear, soil and road dust, and mixed secondary and marine. Exhaust emissions contributed 42% of OP^OH, followed by 21% from brake and tire wear. Similar results were observed for the OP^DTT source apportionment. Furthermore, by linking measured PM_2.5 and OP with census tract level socioeconomic and health outcome data provided by CalEnviroScreen, we found that the most disadvantaged neighborhoods were exposed to both the most toxic particles and the highest particle concentrations. OP^OH exhibited the largest inverse social gradients, followed by OP^DTT and PM_2.5 mass. Finally, OP^OH was the metric most strongly correlated with adverse health outcome indicators.

Solubility of aerosol minor and trace elements in Xiamen Island, Southeast China: Size distribution, health risk and dry deposition

Aerosol element solubility is essential to evaluate the damage to the environment and human health. In this work, the size distribution of total and soluble elements in eight particle size ranges with diameter <0.25, 0.25-0.44, 0.44-1.0, 1.0-1.4, 1.4-2.5, 2.5-10, 10-16 and >16 μm was investigated in Xiamen Island, southeast China from March 2018 to June 2020. The results showed that both total and soluble elements exhibited significant size dependence without obvious seasonal variations, and their relative contributions to PM₁ mass were much lower than in particles larger than 1 μm. The correlations between some elements in soluble fraction were quite different from those in total fraction and the correlations also varied with particle size due to their different solubility. The solubility of Al, Fe, Ag and Cr was relatively low compared with other elements. Moreover, the solubility of Na, Mg, Ca, Mn and Ag was less dependent on particle size while Al, Fe and other trace elements exhibited the highest solubility in PM₁ and the lowest in PM_>10. Overall, the solubility of elements is primarily a function of aerosol origin and size. The carcinogenic risks of metal exposure via inhalation for children (3.31 × 10^-6) and adults (4.42 × 10^-6) were slightly higher than the guideline of cancer risk with >60 % from V. As for non-carcinogenic risk, the hazard index values for children and adults were 1.59 and 0.53, respectively, with Mn, V and Ni together accounting for >85 % of the risk. >85 % of the size-dependent dry deposition fluxes of the selected soluble elements over the Xiamen Bay were contributed by particles larger than 10 μm due to their high deposition velocities. The atmospheric inputs of bioavailable Fe and Cu to the sea exceeded the required amounts relative to inorganic nitrogen to meet the growth of phytoplankton.

Malondialdehyde and anion patterns in exhaled breath condensate among subway workers

BACKGROUND

Underground transportation systems can contribute to the daily particulates and metal exposures for both commuter and subway workers. The redox and metabolic changes in workers exposed to such metal-rich particles have yet to be characterized. We hypothesize that the distribution of nitrosative/oxidative stress and related metabolic biomarkers in exhaled breath condensate (EBC) are modified depending on exposures.

RESULTS

Particulate number and size as well as mass concentration and airborne metal content were measured in three groups of nine subway workers (station agents, locomotive operators and security guards). In parallel, pre- and post-shift EBC was collected daily during two consecutive working weeks. In this biological matrix, malondialdehyde, lactate, acetate, propionate, butyrate, formate, pyruvate, the sum of nitrite and nitrate (ΣNO_x) and the ratio nitrite/nitrate as well as metals and nanoparticle concentrations was determined. Weekly evolution of the log-transformed selected biomarkers as well as their association with exposure variables was investigated using linear mixed effects models with the participant ID as random effect. The professional activity had a strong influence on the pattern of anions and malondialdehyde in EBC. The daily number concentration and the lung deposited surface area of ultrafine particles was consistently and mainly associated with nitrogen oxides variations during the work-shift, with an inhibitory effect on the ΣNO_x. We observed that the particulate matter (PM) mass was associated with a decreasing level of acetate, lactate and ΣNO_x during the work-shift, suggestive of a build-up of these anions during the previous night in response to exposures from the previous day. Lactate was moderately and positively associated with some metals and with the sub-micrometer particle concentration in EBC.

CONCLUSIONS

These results are exploratory but suggest that exposure to subway PM could affect concentrations of nitrogen oxides as well as acetate and lactate in EBC of subway workers. The effect is modulated by the particle size and can correspond to the body's cellular responses under oxidative stress to maintain the redox and/or metabolic homeostasis.

Concentrations, sizes distributions, and seasonal variations of ambient air pollutants (particulates, trace metals) in Daya/Xitun District, Taichung, Central Taiwan: a case study at Taichung Science Park

Taichung Science Park in central Taiwan releases ambient air pollutants to the atmosphere. This issue has attracted much attention over the past few years. This study concerns seasonal concentrations of atmospheric particles and metallic elements and particle size distributions. A M.O.U.D.I sampler is used at a Taichung Science Park sampling site to obtain relevant data. Fe, followed by Al, had the highest average metallic element concentrations in particles of various sizes (PM₁₈, PM₁₀, PM_2.5, PM₁ and PM_<1(0.3)); Cd had the lowest. The average concentrations of metallic elements in particles of various sizes were lowest in the summer. Fe, Al and Cr had the three highest concentrations among all metallic elements for all particles sizes in all seasons. Ambient air particulate pollutants (crustal and anthropogenic metallic elements) were released from a single emission source at Taichung Science Park site.

Aquatic toxicity of particulate matter emitted by five electroplating processes in two marine microalgae species

Electroplating is a widely used group of industrial processes that make a metal coating on a solid substrate. Our previous research studied the concentrations, characteristics, and chemical composition of nano- and microparticles emitted during different electroplating processes. The objective of this study was to evaluate the environmental toxicity of particulate matter obtained from five different electrochemical processes. We collected airborne particle samples formed during aluminum cleaning, aluminum etching, chemical degreasing, nonferrous metals etching, and nickel plating. The toxicity of the particles was evaluated by the standard microalgae growth rate inhibition test. Additionally, we evaluated membrane potential and cell size changes in the microalgae H. akashiwo and P. purpureum exposed to the obtained suspensions of electroplating particles. The findings of this research demonstrate that the aquatic toxicity of electroplating emissions significantly varies between different industrial processes and mostly depends on particle chemical composition and solubility rather than the number of insoluble particles. The sample from an aluminum cleaning workshop was significantly more toxic for both microalgae species compared to the other samples and demonstrated dose and time-dependent toxicity. The samples obtained during chemical degreasing and nonferrous metals etching processes induced depolarization of microalgal cell membranes, demonstrated the potential of chronic toxicity, and stimulated the growth rate of microalgae after 72 h of exposure. Moreover, the sample from a nonferrous metals etching workshop revealed hormetic dose-response toxicity in H. akashiwo, which can lead to harmful algal blooms in the environment.

Dissolved and Suspended Forms of Metals and Metalloids in Snow Cover of Megacity: Partitioning and Deposition Rates in Western Moscow

Concentrations and ratio of dissolved and suspended forms of metals and metalloids (MMs) in snow cover and their deposition rates from the atmosphere in the western part of Moscow were studied. Forms of MMs were separated using a filter with pore diameter of 0.45 μm; their concentrations were measured by ICP-MS and ICP-AES methods. Anthropogenic impact in Moscow caused a significant increase in dust load (2–7 times), concentration of solid particles in snow cover (2–5 times), and mineralization of snow meltwater (5–18 times) compared to the background level. Urban snow contains Sn, Ti, Bi, Al, W, Fe, Pb, V, Cr, Rb, Mo, Mn, As, Co, Cu, Ba, Sb, Mg mainly in suspended form, and Ca and Na in dissolved form. The role of suspended MMs in the city significantly increases compared to the background region due to high dust load, usage of de-icing salts, and the change of acidic background conditions to alkaline ones. Anthropogenic emissions are the main sources of suspended Ca, W, Co, V, Sr, Ti, Mg, Na, Mo, Zn, Fe, Sb, and Cu in the snow cover of traffic zone. These elements’ concentrations in roadside snow cover exceed the background values more than 25 times. The highest concentrations and deposition rates of MMs in the snow of Moscow are localized near the large and medium roads.

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.

The permissive role of TCTP in PM2.5/NNK-induced epithelial-mesenchymal transition in lung cells

Background

Translationally controlled tumor protein (TCTP) is linked to lung cancer. However, upon lung cancer carcinogens stimulation, there were no reports on the relationship between TCTP and lung cell carcinogenic epithelial–mesenchymal transition (EMT). This study was designed to investigate the molecular mechanism of regulation of TCTP expression and its role in lung carcinogens-induced EMT.

Methods

To study the role of TCTP in lung carcinogens [particulate matter 2.5 (PM_2.5) or 4-methylnitrosamino-l-3-pyridyl-butanone (NNK)]-induced EMT, PM_2.5/NNK-treated lung epithelial and non-small cell lung cancer (NSCLC) cells were tested. Cell derived xenografts, human lung cancer samples and online survival analysis were used to confirm the results. MassArray assay, Real-time PCR and Reporter assays were performed to elucidate the mechanism of regulation of TCTP expression. All statistical analyses were performed using GraphPad Prism version 6.0 or SPSS version 20.0.

Results

Translationally controlled tumor protein and vimentin expression were up-regulated in PM_2.5/NNK-treated lung cells and orthotopic implantation tumors. TCTP expression was positively correlated with vimentin in human NSCLC samples. Patients with high expression of TCTP displayed reduced overall and disease-free survival. TCTP overexpression could increase vimentin expression and promote cell metastasis. Furthermore, PM_2.5/NNK stimulation brought a synergistic effect on EMT in TCTP-transfected cells. TCTP knockdown blocked PM_2.5/NNK carcinogenic effect. Mechanically, PM_2.5/NNK-induced TCTP expression was regulated by one microRNA, namely miR-125a-3p, but not by methylation on TCTP gene promoter. The level of TCTP was regulated by its specific microRNA during the process of PM_2.5/NNK stimulation, which in turn enhanced vimentin expression and played a permissive role in carcinogenic EMT.

Conclusions

Our results provided new insights into the mechanisms of TCTP regulatory expression in lung carcinogens-induced EMT. TCTP and miR-125a-3p might act as potential prognostic biomarkers and therapeutic targets for NSCLC.

Ambient fine particulate matter inhibits 15-lipoxygenases to promote lung carcinogenesis

Background

Epidemiological observations have demonstrated that ambient fine particulate matter with d_p < 2.5 μm (PM_2.5) as the major factor responsible for the increasing incidence of lung cancer in never-smokers. However, there are very limited experimental data to support the association of PM_2.5 with lung carcinogenesis and to compare PM_2.5 with smoking carcinogens.

Methods

To study whether PM_2.5 can contribute to lung tumorigenesis in a way similar to smoking carcinogen 4-methylnitrosamino-l-3-pyridyl-butanone (NNK) via 15-lipoxygenases (15-LOXs) reduction, normal lung epithelial cells and cancer cells were treated with NNK or PM_2.5 and then epigenetically and post-translationally examined the cellular and molecular profiles of the cells. The data were verified in lung cancer samples and a mouse lung tumor model.

Results

We found that similar to smoking carcinogen NNK, PM2.5 significantly enhanced cell proliferation, migration and invasion, but reduced the levels of 15-lipoxygenases-1 (15-LOX1) and 15-lipoxygenases-2 (15-LOX2), both of which were also obviously decreased in lung cancer tissues. 15-LOX1/15-LOX2 overexpression inhibited the oncogenic cell functions induced by PM2.5/NNK. The tumor formation and growth were significantly higher/faster in mice implanted with PM2.5- or NNK-treated NCI-H23 cells, accompanied with a reduction of 15-LOX1/15-LOX2. Moreover, 15-LOX1 expression was epigenetically regulated at methylation level by PM2.5/NNK, while both 15-LOX1 and 15-LOX2 could be significantly inhibited by a set of PM2.5/NNK-mediated microRNAs.

Conclusion

Collectively, PM2.5 can function as the smoking carcinogen NNK to induce lung tumorigenesis by inhibiting 15-LOX1/15-LOX2.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1380-z) contains supplementary material, which is available to authorized users.

Source apportionment and source-to-sink transport of major and trace elements in coastal sediments: Combining positive matrix factorization and sediment trend analysis

Major and trace elemental concentrations in coastal marine sediments were incorporated into positive matrix factorization (PMF) to identify potential sources and source contributions. Transport pathways of fine-grained sediments and sediment-bound elements were inferred from sediment trend analysis (STA). The spatial distribution patterns of 21 elements (Co, Cu, Ni, Sr, Zn, V, Ba, Sc, Ga, Pb, Cr, Zr, SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, K₂O, MnO, TiO₂, and P₂O₅) coupled with sediment grain sizes were investigated. The natural and anthropogenic sources of the elements were distinguished by their medium enrichment factors (EFs). Seven sources were recognized by PMF: weathering products, anthropologic emissions, sand, older sediment, biogenic carbonates, products of siliceous organisms, and mine exploitation. Some land-derived elements, including weathering products, anthropogenic-related elements, and mining-related elements, had a significant positive correlation with sediment silt, clay, and organic carbon contents. The spatial patterns of the land-derived elements' concentrations and source contributions were consistent with the sediment transport pathways inferred from the STA. This result revealed that the delivery of the land-derived elements was determined by marine current flows and the associated sediment transport processes. Conversely, elements originating from marine sources, such as sand and older sediment, and from the biological activities of calcareous and siliceous organisms showed little response to sediment transport and deposition processes. Our study links the outputs of statistically oriented approaches (e.g., PMF) to a process-based understanding of elemental transport in marine environments.

Partitioning of particulate matter and elements of suburban continental aerosols between fine and coarse modes

The results presented in this work demonstrate for the first time a distribution of elements in the spectral analysis of aerosols in the suburban continental Balkan Peninsula. Samples were collected in the suburban area of Belgrade (Serbia) in the period from March 2012 till December 2013. Results presented here are from long-term measurements of masses of size-segregated aerosols and macro- and microelements in the range of PM_0.27-16. The following elements were analyzed: Al, Ag, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Ti, Tl, V, and Zn; levels of Be, Hg, and Se were under the detection limits in all samples. Average concentrations and time and seasonal variations of particulate matter (PM) as well as element contents and their percentage shares are given. The results showed the domination of particle content around the accumulation mode in the range of 0.53 < Dp < 1.06 μm, but the fractional distribution of elements showed maximal average concentrations in different fractions depending on the origin of each element. Crustal elements (Al, Ca, Fe, Mg, Mn, Ti, etc.) dominated in coarse mode, while anthropogenic elements (As, Cd, Cu, Pb, Sb, etc.) were mainly distributed in fine mode fractions. Some elements, such are As and Ni, were detected in investigated aerosols only occasionally, while others, such as Ca, Fe, and Mg, were detected in all analyzed samples. The application of multivariate analysis (PCA) demonstrated the connection between the elements of similar origin, in fine fractions mainly of anthropogenic origin, while in coarse mode of crustal origin, indicating the resuspension with contribution of about 40%. The contents of some measured elements were compared with their contents in aerosols in some European suburban areas.

Chemical characterization of size-segregated PM from different public transport modes and implications of source specific contribution to public exposure

To investigate the chemical properties of particulate matter (PM) in different public transport microenvironments in Hong Kong, the coarse (2.5-10 μm) and fine (<2.5 μm) PM samples were collected in three different types of transport modes including Mass Transit Railway (MTR)-Aboveground (AG), MTR Underground (UG), and Bus routes from October 2013 to April 2014. Average PM_2.5 concentrations through UG, AG, and Bus routes were 47.9, 86.8, and 43.8 μg m^-3, respectively, whereas the coarse PM concentrations were 4-5 folds less. The PM_2.5 total metal concentrations of AG route were 2.3 and 3.7 times of UG and BUS routes, respectively, compared to those in the other two routes. The most abundant metals at three stations in PM_2.5 and coarse PM were quite similar and mainly generated by frictional processes of wheels, rails, and brakes of the system as well as by the mechanical wearing of these parts. The most abundant PAH in three routes in PM_2.5 was ATRQN, followed by 2-MNA, and the sum of them contributed to 35 and 42% of total PAHs in coarse PM and PM_2.5, respectively. Crude oils, lubricant oil, diesel emissions would be the major sources of PAHs from MTR aboveground stations. The relative abundance of the n-alkanes among different samples was similar to the PAHs and the carbon preference index (CPI) values of the whole n-alkanes range were consistently from 0.99 to 1.04 among all samples indicating the significant contribution from the vehicle exhaust and fossil fuel burning. The concentrations of hopanes and steranes were higher in PM_2.5 than in coarse PM due to diesel and coal burning. These results may provide a unique opportunity to investigate source specific contribution of the PM pollutants to the commuter exposure in public transport.

Influence of the vegetative cover on the fate of trace metals in retention systems simulating roadside infiltration swales

Large-scale outdoor mesocosms were designed and co-contaminated with metals (Cd, Pb, Zn) and organic compounds to better understand the complex functioning of urban roadside swale environments. Infiltration systems were planted with macrophytes (P. arundinaceae, J. effusus and I. pseudacorus) or grassed, and natural or spiked target metals were monitored over two years. In the non-spiked mesocosms, atmospheric metal inputs were slightly higher than outputs, leading to low metal accumulation in topsoils and to very low outflow water contamination (<0.7% of the initial metal stock). In the spiked infiltration systems that simulated point pollution through water inflow, transfer of the initial stock of metals to the deeper soil layers was quite low and outflow water contamination was very low (<0.6% of the initial stock). The main metal output from these systems occurred in the first days of their installation because of the high metal solubility in water and insufficient plant cover at that time. The infiltration systems stabilized after a few weeks, probably because of stronger sorption to soil aggregates, and because of plant root development. Mephytoextraction in plant roots was more efficient in mesocosms planted with P. arundinacea and grass. Metal phytoextraction in plant aerial parts was also better for grass and P. arundinacea, when considering metal standing stocks instead of their concentration in plants. J. effusus was a good metal accumulator, but its low aboveground biomass development was less favorable to metal removal through harvesting.

Enrichment factors to assess the anthropogenic influence on PM10 in Gijón (Spain)

Thirty-two chemical species were determined in PM₁₀ sampled at a suburban site on the north coast of Spain. Enrichment factors were applied to infer their soil/non-soil origin. The geochemical ratios were calculated using two databases: soil composition from locations in the surroundings of the sampling station and the Earth's average upper-crust composition. In the present study, dissimilarities were found between the enrichment factors obtained using these two databases. Al, Ti, La and Ce were taken as the reference elements to normalise the data, reaching analogous conclusions. Bi, Cd, Cu, Sb, Se, Sn and Zn were associated with predominantly non-soil apportionments. As the relevance of soil/non-soil sources for the other analysed elements was found to be variable, they were probably of mixed origin. Furthermore, pairs of elements showed strong relationships, thus pointing to a common origin. Na-Mg and Co-Ni, with Pearson correlation coefficients above 0.9, were respectively related to marine and industrial apportionments. Enrichment factors have proved to be a useful tool to distinguish the soil/non-soil origin of chemical species present in airborne particulate matter. However, the choice of the reference database for soil composition considerably determined the accuracy of the conclusions.

Magnetic- and particle-based techniques to investigate metal deposition on urban green

Urban green works as a recorder of atmospheric PM. This paper reports on the utility of combining magnetic- and particle-based techniques to investigate PM leaf deposition as a bio-indicator of metal pollution. Ivy (Hedera helix) leaves were collected from five different land use classes, i.e. forest, rural, roadside, industrial, train. Leaf magnetic measurements were done in terms of saturation isothermal remanent magnetization (leaf SIRM), while ca. 40,000 leaf-deposited particles were analyzed through SEM/EDX to estimate the elemental composition. The influence of the different land use classes was registered both magnetically and in terms of metal content. Leaf area-normalized SIRM values ranged from 19.9 to 444.0μA, in the following order forest<rural<roadside<industrial<train. Leaf SIRM showed to be significantly correlated (p<0.01) with the content in Fe, Zn, and Pb, followed by Mn and Cd (p<0.05), while no significant correlation was found with the metals Cr and Cu. Although presenting a similar metal content, roadside and train were magnetically very distinct. By exhibiting a very high content in Pb, and with an Fe content being comparable to the one observed at the forest and rural land uses, the industrial leaf-deposited particles showed to be mainly due to industrial activity. While SEM/EDX is a suitable approach for detailed particle analysis, leaf SIRM of ivy can be used as a rapid discriminatory tool for metal pollution. Their complementary use delivers further knowledge on land use classes reflecting different PM conditions and/or sources.

Airborne iron across major urban centers in South Korea between 1991 and 2012

In this study, the distribution of airborne iron (Fe), one of the most abundant heavy metals in the Earth's crust was investigated to describe the basic features of i'ts pollution in various urban locations. The spatiotemporal distribution of Fe concentrations in seven major South Korean cities exhibited unique patterns to reflect differences as to Fe sources reflected in the relative enrichment in coastal relative to inland areas. In addition, the analysis of long-term trends of different metal species indicated that Fe levels maintained a fairly constant trend, while there had been a noticeable decline in concentrations of other metals (Cd, Cr, Cu, Mn, and Ni). The relative robustness of our correlation analysis was assessed by comparing (1) the Fe concentrations among cities, and (2) Fe with other metals at a given city. Fe concentrations were also partly explainable by the frequency of Asian dust events in most cities, with the observed spatial gradients in such relationships.