Tropospheric air pollution: ozone, airborne toxics, polycyclic aromatic hydrocarbons, and particles

Evaluation of the impact of urban pollution on the quality of skin: a multicentre study in Mexico

OBJECTIVE

After pilot and preliminary studies aimed at identifying pertinent biochemical parameters, a multicenter clinical study was performed to evaluate the effect of pollution on human skin.

METHODS

The clinical study was performed in collaboration with the 'Centre Régional de lutte contre le cancer de Montpellier' and the 'National Institute of Public Health of Mexico' on 96 subjects in Mexico City (exposed to pollution) and 93 subjects in Cuernavaca (less exposed to pollution). Both biochemical and clinical skin parameters were studied.

RESULTS

The study demonstrated significant quantitative and qualitative modifications of parameters related to sebum excretion in Mexico City compared to Cuernavaca one: An increased level of sebum excretion rate, a lower level of vitamin E and squalene in sebum, an increase of lactic acid and a higher erythematous index on the face of the subjects. In the stratum corneum, a significant higher level of carbonylated proteins and a lower level of IL 1α were noticed, as well as a decrease of ATP concentration with a decrease of chymotrysin like activity, without modifications of corneodesmosin content and trypsin like activity. From a clinical point of view, a higher frequency of atopic and urticarial skins, a higher frequency of red dermographism, an important seborrheic status at the forehead level and a lower level of dandruffs were noted in Mexico City population. The analysis taking into account the sex does not modify the observed results.

CONCLUSION

The study demonstrated an important impact of polluted environmental conditions on skin quality, evidencing important modifications of superficial biochemical parameters. The cause/effects relationships of these modifications remain, however, to be further assessed by a complementary in vitro/in vivo approaches.

Unexpected chemistry from the reaction of naphthyl and acetylene at combustion-like temperatures

The hydrogen abstraction/acetylene addition (HACA) mechanism has long been viewed as a key route to aromatic ring growth of polycyclic aromatic hydrocarbons (PAHs) in combustion systems. However, doubt has been drawn on the ubiquity of the mechanism by recent electronic structure calculations which predict that the HACA mechanism starting from the naphthyl radical preferentially forms acenaphthylene, thereby blocking cyclization to a third six-membered ring. Here, by probing the products formed in the reaction of 1- and 2-naphthyl radicals in excess acetylene under combustion-like conditions with the help of photoionization mass spectrometry, we provide experimental evidence that this reaction produces 1- and 2-ethynylnaphthalenes (C12 H8 ), acenaphthylene (C12 H8 ) and diethynylnaphthalenes (C14 H8 ). Importantly, neither phenanthrene nor anthracene (C14 H10 ) was found, which indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead.

Ozone exposure triggers insulin resistance through muscle c-Jun N-terminal kinase activation

A growing body of evidence suggests that exposure to traffic-related air pollution is a risk factor for type 2 diabetes. Ozone, a major photochemical pollutant in urban areas, is negatively associated with fasting glucose and insulin levels, but most aspects of this association remain to be elucidated. Using an environmentally realistic concentration (0.8 parts per million), we demonstrated that exposure of rats to ozone induced whole-body insulin resistance and oxidative stress, with associated endoplasmic reticulum (ER) stress, c-Jun N-terminal kinase (JNK) activation, and disruption of insulin signaling in skeletal muscle. Bronchoalveolar lavage fluids from ozone-treated rats reproduced this effect in C2C12 myotubes, suggesting that toxic lung mediators were responsible for the phenotype. Pretreatment with the chemical chaperone 4-phenylbutyric acid, the JNK inhibitor SP600125, or the antioxidant N-acetylcysteine alleviated insulin resistance, demonstrating that ozone sequentially triggered oxidative stress, ER stress, and JNK activation to impair insulin signaling in muscle. This study is the first to report that ozone plays a causative role in the development of insulin resistance, suggesting that it could boost the development of diabetes. We therefore provide a potential mechanism linking pollutant exposure and the increased incidence of metabolic diseases.

Formation of 5- and 6-methyl-1H-indene (C10H10) via the reactions of the para-tolyl radical (C6H4CH3) with allene (H2CCCH2) and methylacetylene (HCCCH3) under single collision conditions

Flux contour map for the reactions of the p-tolyl radical with allene-d4 and methylacetylene-d4 at collision energies of around 48 kJ mol⁻¹.

Metal cluster-deposited graphene as an adsorptive material for m-xylene

m-Xylene weakly adsorbs on graphene and silver cluster doped graphene, but it has excellent interaction with platinum cluster doped graphene.

A crossed molecular beam and ab initio study on the formation of 5- and 6-methyl-1,4-dihydronaphthalene (C11H12) via the reaction of meta-tolyl (C7H7) with 1,3-butadiene (C4H6)

The crossed molecular beam reactions of the meta-tolyl radical with 1,3-butadiene and D6-1,3-butadiene were conducted at collision energies of 48.5 kJ mol⁻¹ and 51.7 kJ mol⁻¹.

Formation of 2- and 1-methyl-1,4-dihydronaphthalene isomers via the crossed beam reactions of phenyl radicals (C6H5) with isoprene (CH2C(CH3)CHCH2) and 1,3-pentadiene (CH2CHCHCHCH3)

Crossed molecular beam reactions were exploited to elucidate the chemical dynamics of the reactions of phenyl radicals with isoprene and with 1,3-pentadiene at a collision energy of 55 ± 4 kJ mol⁻¹.

A combined crossed molecular beam and theoretical investigation of the reaction of the meta-tolyl radical with vinylacetylene – toward the formation of methylnaphthalenes

Flux contour map for the reactive scattering channel of meta-tolyl radical with vinylacetylene.

Fire in Australian savannas: from leaf to landscape

Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km2) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.

Novel TiO2/graphene oxide functionalized with a cobalt complex for significant degradation of NOx and CO

A TiO₂/FGO composite manifests high photocatalytic properties for NO_x and CO removal as high as three times more than that of bare TiO₂.

Mechanistic and kinetic studies on OH-initiated atmospheric oxidation degradation of benzo[α]pyrene in the presence of O2 and NO(x)

The degradation of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere can lead to toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. This paper aimed to investigate the mechanism of the OH-initiated oxidation degradation of benzo[α]pyrene (BaP), a cancer risk indicator. High-accuracy molecular orbital calculations were carried out, and all of the possible degradation pathways were discussed. The theoretical results were compared with the available experimental observation. The possible secondary reactions were also investigated. The rate constants of the crucial elementary steps were evaluated by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The dominant degradation products involve benzo[α]pyren-ol, nitro-benzo[α]pyrene, benzo[α]pyrene-7,10-dione as well as several ring-opened products such as alkyl substituted benzanthraldehyde et al. In particular, water plays an important role in the degradation pathways leading to the formation of nitro-benzo[α]pyrene. This work provides a comprehensive investigation of the OH-initiated degradation of BaP and should help to clarify its potential risk.

Assessment of ethylene diurea-induced protection in plants against ozone phytotoxicity

Urbanization, industrialization and unsustainable utilization of natural resources have made tropospheric ozone (03) one of the world's most significant air pollutants. Past studies reveal that 0 3 is a phytotoxic air pollutant that causes or enhances food insecurity across the globe. Plant sensitivity, tolerance and resistance to 0 3 involve a wide array of responses that range from growth to the physiological, biochemical and molecular. Although plants have an array of defense systems to combat oxidative stress from 0 3 exposure, they still suffer sizable yield reductions. In recent years, the ground-level 0 3 concentrations to which crop plants have been exposed have caused yield loses that are economically damaging. Several types of chemicals have been applied or used to mitigate the effects produced by 0 3 on plants. These include agrochemicals (fungicides, insecticides, plant growth regulators), natural antioxidants, and others. Such treatments have been effective to one degree to another, in ameliorating Or generated stress in plants. Ethylene diurea (EDU) has been the most effective protectant used and has also served as a monitoring agent for assessing plant yield losses from 0 3 exposure. In this review, we summarize the data on how EDU has been used, the treatment methods tested, and application doses found to be both protective and toxic in plants. We have also summarized data that address the nature and modes of action (biophysical and biochemical) of EDU. In general, the literature discloses that EDU is effective in reducing ozone damage to plants, and indicates that EDU should be more widely used on 0 3 sensitive plants as a tool for biomonitoring of 0 3 concentrations. Biomonitoring studies that utilize EDU are very useful for rural and remote areas and in developing countries where 0 3 monitoring is constrained from unavailability of electricity. The mechanism(s) by which EDU prevents 0 3 toxicity in plants is still not completely known. EDU possesses great utility for screening plant sensitivity under field conditions in areas that experience high 0 3 concentrations, because EDU prevents 0 3 toxicity only in 0 3 sensitive plants. Ozone-resistant plants do not respond positively to EDU applications. However, EDU application dose and frequency must be standardized before it can be effectively and widely used for screening 0 3 sensitivity in plants. EDU acts primarily by enhancing biochemical plant defense and delaying Or induced senescence, thereby reducing chlorophyll loss, and maintaining physiological efficiency and primary metabolites; these actions enhance growth, biomass and yield of plants. We believe that future studies are needed to better address the EDU dose response relationship for many plant species, and to screen for new cultivars that can resist 0 3 stress. Although some research on the physiological and biochemical mechanisms of action of EDU have been performed, the new 'omics' tools have not been utilized to evaluate EDUs mechanism of action. Such data are needed, as is gene expression and proteome profiling studies on EDU-treated and -untreated plants.

Formation of 6-methyl-1,4-dihydronaphthalene in the reaction of the p-tolyl radical with 1,3-butadiene under single-collision conditions

Crossed molecular beam reactions of p-tolyl (C7H7) plus 1,3-butadiene (C4H6), p-tolyl (C7H7) plus 1,3-butadiene-d6 (C4D6), and p-tolyl-d7 (C7D7) plus 1,3-butadiene (C4H6) were carried out under single-collision conditions at collision energies of about 55 kJ mol(-1). 6-Methyl-1,4-dihydronaphthalene was identified as the major reaction product formed at fractions of about 94% with the monocyclic isomer (trans-1-p-tolyl-1,3-butadiene) contributing only about 6%. The reaction is initiated by barrierless addition of the p-tolyl radical to the terminal carbon atom of the 1,3-butadiene via a van der Waals complex. The collision complex isomerizes via cyclization to a bicyclic intermediate, which then ejects a hydrogen atom from the bridging carbon to form 6-methyl-1,4-dihydronaphthalene through a tight exit transition state located about 27 kJ mol(-1) above the separated products. This is the dominant channel under the present experimental conditions. Alternatively, the collision complex can also undergo hydrogen ejection to form trans-1-p-tolyl-1,3-butadiene; this is a minor contributor to the present experiment. The de facto barrierless formation of a methyl-substituted aromatic hydrocarbons by dehydrogenation via a single event represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated analogues in combustion flames and the interstellar medium.

Spatiotemporal modeling of ozone levels in Quebec (Canada): a comparison of kriging, land-use regression (LUR), and combined Bayesian maximum entropy-LUR approaches

BACKGROUND

Ambient air ozone (O3) is a pulmonary irritant that has been associated with respiratory health effects including increased lung inflammation and permeability, airway hyperreactivity, respiratory symptoms, and decreased lung function. Estimation of O3 exposure is a complex task because the pollutant exhibits complex spatiotemporal patterns. To refine the quality of exposure estimation, various spatiotemporal methods have been developed worldwide.

OBJECTIVES

We sought to compare the accuracy of three spatiotemporal models to predict summer ground-level O3 in Quebec, Canada.

METHODS

We developed a land-use mixed-effects regression (LUR) model based on readily available data (air quality and meteorological monitoring data, road networks information, latitude), a Bayesian maximum entropy (BME) model incorporating both O3 monitoring station data and the land-use mixed model outputs (BME-LUR), and a kriging method model based only on available O3 monitoring station data (BME kriging). We performed leave-one-station-out cross-validation and visually assessed the predictive capability of each model by examining the mean temporal and spatial distributions of the average estimated errors.

RESULTS

The BME-LUR was the best predictive model (R2 = 0.653) with the lowest root mean-square error (RMSE ;7.06 ppb), followed by the LUR model (R2 = 0.466, RMSE = 8.747) and the BME kriging model (R2 = 0.414, RMSE = 9.164).

CONCLUSIONS

Our findings suggest that errors of estimation in the interpolation of O3 concentrations with BME can be greatly reduced by incorporating outputs from a LUR model developed with readily available data.

Validation of OMI HCHO data and its analysis over Asia

OMI HCHO is validated over the continental US (CONUS), and used to analyze regional sources in Northeast Asia (NA) and Southeast Asia (SA). OMI HCHO Version 2.0 data show unrealistic trends, which prompted the production of a corrected OMI HCHO data set. EOF and SVD are utilized to compare the spatial and temporal variability between OMI HCHO against GOME and SCIAMACHY, and against GEOS-Chem. CONUS HCHO chemistry is well studied; its concentrations are greatest in the southeastern US with annual cycle maximums corresponding to the summer vegetation. The corrected OMI HCHO agrees with this understanding as well as with the other sensors measurements and has no unrealistic trends. In NA the annual cycle is super-posed by extremely large concentrations in polluted mega-cities. The other sensors generally agree with NA's OMI HCHO regional distribution, but megacity signal is not seen in GEOS-Chem. Our study supports the findings proposed by others that the emission inventory used in GEOS-Chem significantly underestimates anthropogenic influence on HCHO emission over megacities. The persistent mega-city signal is also present in SA. In SA the spatial and temporal patterns of OMI HCHO show a maximum in the dry season. The patterns are in remarkably good agreement with fire counts, which illustrates that the variability of HCHO over SA is strongly influenced by biomass burning. The corrected OMI HCHO data has realistic trends, conforms to well-known sources over CONUS, and has shown a stationary large concentration over polluted Asian mega-cities, and a widespread biomass burning in SA.

Dynamics of chlorine atom reactions with hydrocarbons: insights from imaging the radical product in crossed beams

We present a comprehensive overview of our ongoing studies applying dc slice imaging in crossed molecular beams to probe the dynamics of chlorine atom reactions with polyatomic hydrocarbons. Our approach consists in measuring the full velocity-flux contour maps of the radical products using vacuum ultraviolet "soft" photoionization at 157 nm. Our overall goal is to extend the range of chemical dynamics investigations from simple triatomic or tetraatomic molecules to systematic investigations of a sequence of isomers or a homologous series of reactants of intermediate size. These experimental investigations are augmented by high-level ab initio calculations which, taken together, reveal trends in product energy and angular momentum partitioning and offer deep insight into the reaction mechanisms as a function of structure, bonding patterns, and kinematics. We explore these issues in alkanes, for which only direct reactive encounters are found, and in unsaturated hydrocarbons, for which an addition-elimination mechanism competes with direct abstraction. The results for alkene addition-elimination in particular suggest a new view of these reactions: The only pathway to HCl elimination is accessed by means of roaming excursions of the Cl atom from the strongly bound adduct.

Formation of nitroanthracene and anthraquinone from the heterogeneous reaction between NO2 and anthracene adsorbed on NaCl particles

Oxidative derivatives of polycyclic aromatic hydrocarbons (PAHs), that is, nitro-PAHs and quinones, are classed as hazardous semivolatile organic compounds but their formation mechanism from the heterogeneous reactions of PAHs adsorbed on atmospheric particles is not well understood. The heterogeneous reaction of NO2 with anthracene adsorbed on NaCl particles under different relative humidity (RH 0-60%) was investigated under dark conditions at 298 K. The formation of the major products, 9,10-anthraquinone (9,10-AQ) and 9-nitroanthracene (9-NANT), were determined to be second-order reactions with respect to NO2 concentration. The rate of formation of 9,10-AQ under low RH (0-20%) increased as the RH increased but decreased when the RH was further increased in high RH (40-60%). In contrast, the rate of formation of 9-NANT across the whole RH range (0-60%) decreased significantly with increasing RH. Two different reaction pathways are discussed for the formation of 9,10-AQ and 9-NANT, respectively, and both are considered to be coupled to the predominant reaction of NO2 with the NaCl substrate. These results suggest that relative humidity, which controls the amount of surface adsorbed water on NaCl particles, plays an important role in the heterogeneous reaction of NO2 with adsorbed PAHs.

Mo-modified Pd/Al₂O₃ catalysts for benzene catalytic combustion

Mo-modified Pd/Al₂O₃ catalysts were prepared by an impregnation method and tested for the catalytic combustion of benzene. The catalysts were characterized by N₂ isothermal adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of NH₃ (NH₃-TPD), H₂ temperature-programmed reduction (H₂-TPR), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The results showed that the addition of Mo effectively improved the activity and stability of the Pd/Al₂O₃ catalyst by increasing the dispersion of Pd active components, changing the partial oxidation state of palladium and increasing the oxygen species concentration on the surface of catalyst. In the case of the Pd-Mo/Al₂O₃ catalyst, benzene conversion of 90% was obtained at temperatures as low as 190°C, which was 45°C lower than that for similar performance with the Pd/Al₂O₃ catalyst. Moreover, the 1.0% Pd-5% Mo/Al₂O₃ catalyst was more active than the 2.0% Pd/Al₂O₃ catalyst. It was concluded that Pd and Mo have a synergistic effect in benzene catalytic combustion.

Multiple regression analysis in modeling of columnar ozone in Peninsular Malaysia

This study aimed to predict monthly columnar ozone (O3) in Peninsular Malaysia by using data on the concentration of environmental pollutants. Data (2003-2008) on five atmospheric pollutant gases (CO2, O3, CH4, NO2, and H2O vapor) retrieved from the satellite Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) were employed to develop a model that predicts columnar ozone through multiple linear regression. In the entire period, the pollutants were highly correlated (R = 0.811 for the southwest monsoon, R = 0.803 for the northeast monsoon) with predicted columnar ozone. The results of the validation of columnar ozone with column ozone from SCIAMACHY showed a high correlation coefficient (R = 0.752-0.802), indicating the model's accuracy and efficiency. Statistical analysis was utilized to determine the effects of each atmospheric pollutant on columnar ozone. A model that can retrieve columnar ozone in Peninsular Malaysia was developed to provide air quality information. These results are encouraging and accurate and can be used in early warning of the population to comply with air quality standards.

Role of water molecule in the gas-phase formation process of nitrated polycyclic aromatic hydrocarbons in the atmosphere: a computational study

Nitro-PAHs are globally worrisome air pollutants because their high direct-acting mutagenicity and carcinogenicity. A mechanistic understanding of their formation is of crucial importance for successful prevention of their atmospheric pollution. Here, the formation of nitro-PAHs arising from the OH-initiated and NO3-initiated atmospheric reactions of PAHs was investigated by using quantum chemical calculations. It is widely assumed that OH or NO3 radicals attack on the C atoms of the aromatic rings in the PAH molecule, followed by the addition of NO2 to the OH-PAH or NO3-PAH adducts at the ortho position and the loss of water or nitric acid to form nitro-PAHs. However, calculations show that the direct loss of water from the OH-NO2-PAH adducts via the unimolecular decomposition is energetically unfavorable. This study reveals for the first time that water molecule plays an important catalytic effect on the loss of water from the OH-NO2-PAH adducts and promotes the formation of nitro-PAHs. In addition, the introduction of water unwraps new formation pathway through the addition of NO2 to the OH-PAH or NO3-PAH adduct at the para position. The individual and overall rate constants for the addition reactions of PAHs with OH and NO3 radicals were deduced by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory.

Polycyclic aromatic hydrocarbons (PAHs) in ambient aerosols from Beijing: characterization of low volatile PAHs by positive-ion atmospheric pressure photoionization (APPI) coupled with Fourier transform ion cyclotron resonance

Aromatic fractions derived from aerosol samples were characterized by gas chromatography and mass spectrometry (GC-MS), high temperature simulated distillation (SIMDIS), and positive-ion atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. It was found that about 27 wt % compounds in aromatic fractions could not be eluted from a GC column and some large molecule PAHs were neglected in GC-MS analysis. APPI FT-ICR MS was proven to be a powerful approach for characterizing the molecular composition of aromatics, especially for the large molecular species. An aromatic sample from Beijing urban aerosol was successfully characterized by APPI FT-ICR MS. Results showed that most abundant aromatic compounds in PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) were highly condensed hydrocarbons with 4-8 aromatic rings and their homologues with very short alkyl chains. Furthermore, heteroatom-containing hydrocarbons were found as the significant components of the aromatic fractions: O1, O2, N1, and S1 class species with 10-28 DBEs (double bond equivalents) and 14-38 carbon numbers were identified by APPI FT-ICR MS. The heteroatom PAHs had similar DBEs and carbon number distribution as regular PAHs.

Evaluation of the reaction artifacts in an annular denuder-based sampler resulting from the heterogeneous ozonolysis of naphthalene

The heterogeneous ozonolysis of naphthalene adsorbed on XAD-4 resin was studied using an annular denuder technique. The experiments involved depositing a known quantity of naphthalene on the XAD-4 resin and then measuring the quantity of the solid naphthalene that reacted away under a constant flow of gaseous ozone (0.064 to 4.9 ppm) for a defined amount of time. All experiments were performed at room temperature (26 to 30 °C) and atmospheric pressure. The kinetic rate coefficient for the ozonolysis reaction of naphthalene adsorbed on XAD-4 resin is reported to be (10.1 ± 0.4) × 10(-19) cm(3) molecule(-1) s(-1) (error is 2σ, precision only). This value is five times greater than the currently recommended literature value for the homogeneous gas phase reaction of naphthalene with ozone. The obtained rate coefficient is used to evaluate reaction artifacts from field concentration measurements of naphthalene, acenaphthene, and phenanthrene. The observed uncertainties associated with field concentration measurements of naphthalene, acenaphthene, and phenanthrene are reported to be much higher than the uncertainties associated with the artifact reactions. Consequently, ozone reaction artifact appears to be negligible compared to the observed field measurement uncertainty results.

Oxidation and nitration of tyrosine by ozone and nitrogen dioxide: reaction mechanisms and biological and atmospheric implications

The nitration of tyrosine by atmospheric oxidants, O3 and NO2, is an important cause for the spread of allergenic diseases. In the present study, the mechanism and pathways for the reaction of tyrosine with the atmospheric oxidants O3 and NO2 are studied using DFT-M06-2X, B3LYP, and B3LYP-D methods with the 6-311+G(d,p) basis set. The energy barrier for the initial oxidation reactions is also calculated at the CCSD(T)/6-31+G(d,p) level of theory. The reaction is studied in gas, aqueous, and lipid media. The initial oxidation of tyrosine by O3 proceeds by H atom abstraction and addition reactions and leads to the formation of six different intermediates. The subsequent nitration reaction is studied for all the intermediates, and the results show that the nitration affects both the side chain and the aromatic ring of tyrosine. The rate constant of the favorable oxidation and nitration reaction is calculated using variational transition state theory over the temperature range of 278-350 K. The spectral properties of the oxidation and nitration products are calculated at the TD-M06-2X/6-311+G(d,p) level of theory. The fate of the tyrosine radical intermediate is studied by its reaction with glutathione antioxidant. This study provides an enhanced understanding of the oxidation and nitration of tyrosine by O3 and NO2 in the context of improving the air quality and reducing the allergic diseases.

Distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in forest soils from urban to rural areas in the Pearl River Delta of Southern China

The upper layer of forest soils (0-20 cm depth) were collected from urban, suburban, and rural areas in the Pearl River Delta of Southern China to estimate the distribution and the possible sources of polycyclic aromatic hydrocarbons (PAHs). Total concentrations of PAHs in the forest soils decreased significantly along the urban-suburban-rural gradient, indicating the influence of anthropogenic emissions on the PAH distribution in forest soils. High and low molecular weight PAHs dominated in the urban and rural forest soils, respectively, implying the difference in emission sources between the areas. The values of PAH isomeric diagnostic ratios indicated that forest soil PAHs were mainly originated from traffic emissions, mixed sources and coal/wood combustion in the urban, suburban and rural areas, respectively. Principal component analysis revealed that traffic emissions, coal burning and residential biomass combustion were the three primary contributors to forest soil PAHs in the Pearl River Delta. Long range transportation of PAHs via atmosphere from urban area might also impact the PAHs distribution in the forest soils of rural area.

Source, distribution, and health risk assessment of polycyclic aromatic hydrocarbons in urban street dust from Tianjin, China

To better assess and understand potential health risk of urban residents exposed to urban street dust, the total concentration, sources, and distribution of 16 polycyclic aromatic hydrocarbons (PAHs) in 87 urban street dust samples from Tianjin as a Chinese megacity that has undergone rapid urbanization were investigated. In the meantime, potential sources of PAHs were identified using the principal component analysis (PCA), and the risk of residents' exposure to PAHs via urban street dust was calculated using the Incremental Lifetime Cancer Risk (ILCR) model. The results showed that the total PAHs (∑PAHs) in urban street dust from Tianjin ranged from 538 μg kg(-1) to 34.3 mg kg(-1), averaging 7.99 mg kg(-1). According to PCA, the two to three- and four to six-ring PAHs contributed 10.3 and 89.7 % of ∑PAHs, respectively. The ratio of the sum of major combustion specific compounds (ΣCOMB) / ∑PAHs varied from 0.57 to 0.79, averaging 0.64. The ratio of Ant/(Ant + Phe) varied from 0.05 to 0.41, averaging 0.10; Fla/(Fla + Pyr) from 0.40 to 0.68, averaging 0.60; BaA/(BaA + Chry) from 0.29 to 0.51, averaging 0.38; and IcdP/(IcdP + BghiP) from 0.07 to 0.37, averaging 0.22. The biomass combustion, coal combustion, and traffic emission were the main sources of PAHs in urban street dust with the similar proportion. According to the ILCR model, the total cancer risk for children and adults was up to 2.55 × 10(-5) and 9.33 × 10(-5), respectively.

Reaction dynamics of the 4-methylphenyl radical (C6H4CH3; p-tolyl) with isoprene (C5H8) – formation of dimethyldihydronaphthalenes

Reaction dynamics and energetics of 4-methylphenyl radical with isoprene are reported under single collision condition at collision energy of 58 kJ mol⁻¹ by exploiting the crossed molecular beam technique and electronic structure calculations.

Polycyclic aromatic hydrocarbons in surface soil across the Tibetan Plateau: spatial distribution, source and air-soil exchange

There are limited data on polycyclic aromatic hydrocarbons (PAHs) in both the atmosphere and soil of the Tibetan Plateau (TP). Concentrations of PAHs were therefore measured in 13 XAD resin-based passive air samplers and 41 surface (0-5 cm) soil samples across the TP. The average concentration of atmospheric PAHs was 5.55 ng/m(3), which was lower than that reported for other background areas, but higher than the Arctic. Concentrations in the soils fell in a wide range from 5.54 to 389 ng/g, with an average of 59.9 ng/g. Elevation was found to play an important role in determining the spatial distribution of soil PAHs. The air-soil exchange state showed that the soils of the TP will likely remain as a sink for high molecular weight PAHs, but may become a potential "secondary source" for low molecular weight PAHs.

Heterogeneous uptake and adsorption of gas-phase formic acid on oxide and clay particle surfaces: the roles of surface hydroxyl groups and adsorbed water in formic acid adsorption and the impact of formic acid adsorption on water uptake

Organic acids in the atmosphere are ubiquitous and are often correlated with mineral dust aerosol. Heterogeneous chemistry and the uptake of organic acids on mineral dust particles can potentially alter the properties of the particle. In this study, heterogeneous uptake and reaction of formic acid, HCOOH, the most abundant carboxylic acid present in the atmosphere, on oxide and clays of the most abundant elements, Si and Al, present in the Earth's crust are investigated under dry and humid conditions. In particular, quantitative adsorption measurements using a Quartz Crystal Microbalance (QCM) coupled with spectroscopic studies using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy are combined to allow for both quantification of the amount of uptake and identification of distinct adsorbed species formed on silica, alumina, and kaolinite particle surfaces at 298 K. These oxides and clay particles show significant differences in the extent and speciation of adsorbed HCOOH due to inherent differences in surface -OH group reactivity. Adsorbed water, controlled by relative humidity, can increase the irreversible uptake of formic acid. Interestingly, the resulting layer of adsorbed formate on the particle surface decreases the particle hydrophilicity thereby decreasing the amount of water taken up by the surface as measured by QCM. Atmospheric implications of this study are discussed.

Exposure to elevated ozone levels differentially affects the antioxidant capacity and the redox homeostasis of two subtropical Phaseolus vulgaris L. varieties

Ozone (O3) has become one of the most toxic air pollutants to plants worldwide. However, investigations on O3 impacts on crops health and productivity in South America countries are still scarce. The present study analyzed the differences on the enzymatic and non-enzymatic antioxidant system in foliar tissue of two subtropical Phaseolus vulgaris varieties exposed to high O3 concentration. Both varieties were negatively impacted by the pollutant, but the responses between each variety were quite distinct. Results revealed that Irai has higher constitutive levels of reactive oxygen species (ROS) and ascorbate (AsA) concentration, but lower total thiol levels and catalase immunocontent. In this variety catalase protein concentration was increased after O3 exposure, indicating a better cellular capacity to reduce hydrogen peroxide. On the opposite, Fepagro 26-exposed plants increased ROS generation and AsA concentration, but had the levels of total thiol content and catalase protein unchanged. Furthermore, O3 treatment reduced the levels of chlorophylls a and b, and the relationship analysis between the chlorophyll ratio (a/b) and protein concentration were positively correlated indicating that photosynthetic apparatus is compromised, and thus probably is the biomass acquisition on Fepagro 26. Differently, O3 treatment of Irai did not affect chlorophylls a and b content, and loss on the protein content was lower. Altogether, these data suggest that early accumulation of ROS on Fepagro 26 are associated with an insufficient leaf antioxidant capacity, which leads to cell structure disruption and impairs the photosynthesis. Irai seems to be more tolerant to O3 toxic effects than Fepagro 26, and the observed differences on O3 sensitivity between the two varieties are apparently based on constitutive differences involved in the maintenance of intracellular redox homeostasis.

Development of a biphasic electroreactor with a wet scrubbing system for the removal of gaseous benzene

An efficient, continuous flow electroreactor system comprising a scrubbing column (for absorption) and a biphasic electroreactor (for degradation) was developed to treat gas streams containing benzene. Initial benzene absorption studies using a continuous flow bubble column containing absorbents like 40% sulfuric acid, 10% silicone oil (3, 5, 10 cSt), or 100% silicone oil showed that 100% silicone oil is the most suitable. A biphasic batch electroreactor based on 50 mL of silicone oil and 100 mL of activated Co(III) (activated electrochemically) in 40% sulfuric acid demonstrated that indirect oxidation of benzene is possible by Co(III). Combined experiments on the wet scrubbing column and biphasic electroreactor (BP-ER) were performed to determine the feasibility of benzene removal, which is reside in the silicone oil medium. In semidynamic scrubbing with BP-ER experiments using an aqueous electroreactor volume of 2 L, and an inlet gas flow and a gaseous benzene concentration were 10 Lmin(-1) and 100 ppm, respectively, benzene removal efficiency is 75% in sustainable way. The trend of CO2 evolution is well correlated with benzene recovery in the BP-ER. The addition of sodiumdodecyl sulfate (SDS) enhanced the recovery of silicone oil without affecting benzene removal. This process is promising for the treatment of high concentrations of gaseous benzene.

Phototransformations of dinitropyrene isomers on models of the atmospheric particulate matter

The 1,6 and 1,8-dinitropyrenes (DNP) isomers are strong mutagens and carcinogens encountered in diesel exhaust and airborne particles. Relative photodegradation rates were determined and some products were characterized when these isomers were irradiated adsorbed onto models of the atmospheric matter. These are compared to their photochemical behavior in a polar nonprotic solvent. The 1,8-DNP isomer is three times more reactive than the 1,6-DNP when irradiated adsorbed onto silica gel surfaces, while the reverse order is observed in solution, demonstrating the influence of structural differences and environmental effects on the photoreactivity. Oxygen is a key factor in the formation of pyrenediones from 1,8-DNP in solution and on silica gel which is not the case for 1,6-DNP. The average pore diameter (2.5 versus 6.0 nm) of the silica surfaces induces a significant change in the product distribution and relative yields of 1,8-DNP because pyrenediones or 8-hydroxy-1-nitropyrene are not produced in the smaller pore silica. A 6-hydroxy-1-nitropyrene product is observed both in acidic alumina and silica (6.0 nm) surfaces. On acidic alumina the rates of phototransformation of the isomers are equal, a significant increase in the relative yield of the hydroxynitropyrene product is observed compared to the silica and unidentified products in which the absence of NO₂ and pyrene absorption bands were observed, demonstrating the surface effect on the photodegradation. Overall, the presence of some products indicates the occurrence of a nitro-nitrite rearrangement on the surface with the participation of a pyrenoxy radical as their precursor.

Unexpectedly high indoor hydroxyl radical concentrations associated with nitrous acid

The hydroxyl (OH) radical is the most important oxidant in the atmosphere since it controls its self-oxidizing capacity. The main sources of OH radicals are the photolysis of ozone and the photolysis of nitrous acid (HONO). Due to the attenuation of solar radiation in the indoor environment, the possibility of OH formation through photolytic pathways indoors has been ignored up to now. In the indoor air, the ozonolysis of alkenes has been suggested as an alternative route of OH formation. Models and indirect measurements performed up to now according to this hypothesis suggest concentrations of OH radicals on the order of 10(4)-10(5) molecules per cubic centimeter. Here, we present direct measurements of significant amounts of OH radicals of up to 1.8⋅10(6) molecules per cubic centimeter during an experimental campaign carried out in a school classroom in Marseille. This concentration is on the same order of magnitude of outdoor OH levels in the urban scenario. We also show that photolysis of HONO is an important source of OH radicals indoors under certain conditions (i.e., direct solar irradiation inside the room). Additionally, the OH concentrations were found to follow a linear dependence with the product J(HONO)⋅[HONO]. This was also supported by using a simple quasiphotostationary state model on the OH radical budget. These findings force a change in our understanding of indoor air quality because the reactivity linked to OH would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air.

A wintertime study of polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor air in a big student residence in Algiers, Algeria

The wintertime concentrations and diel cycles of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) associated to atmospheric particulate matter with aerodynamic diameter lesser than 10 μm were determined at the biggest student residence in Algeria located in Bab-Ezzouar, 15 km southeast from Algiers city area. Samplings were carried out from December 2009 to March 2010, and organic compounds were characterized using gas chromatography coupled with mass spectrometric detection. Volatile PAHs were also monitored inside some student residence rooms in order to evaluate the impact of indoor air pollution to student health. For the sake of comparison, aerial concentrations of n-alkanes and PAHs were determined in parallel in the Oued Smar industrial zone and two suburban areas, all located in Algiers. Total concentrations recorded in CUB1 student residence ranged from 101 to 204 ng m(-3) for n-alkanes and from 8 to 87 ng m(-3) for PAHs. Diel cycles have shown that, while concentrations of n-alkanes peaked at morning and afternoon-evening and dropped at night, those of PAHs exhibited higher levels at morning and night and lower levels at afternoon-evening, likely due to the reactivity of some PAHs. As expected, the indoor levels of PAHs were larger than in the outdoor of the student residence and were of serious health concern. Overall, the concentrations of n-alkanes and PAHs were as high as those observed in the industrial zone and higher than the two suburban sites.