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

Aromatic photonitration in homogeneous and heterogeneous aqueous systems

This work describes the nitration of aromatics upon near-UV photolysis of nitrate and nitrite in aqueous solution and upon photocatalytic oxidation of nitrite in TiO2 suspensions. Phenol is used in this work as a model aromatic molecule and as a probe for *NO2/N2O4. The photoinduced nitration of phenol in aqueous systems occurs upon the reaction between phenol and *NO2 or N2O4, and is enhanced by the photocatalytic oxidation of nitrite to *NO2 by TiO2. Aromatic photonitration in the liquid phase can play a relevant role in the formation of nitroaromatics in natural waters and atmospheric hydrometeors, thus being a potential pathway for the condensed-phase nitration of aromatics. Furthermore, the photoinduced oxidation of nitrite to nitrogen dioxide suggests a completely new role for nitrite in natural waters and atmospheric aerosols.

Laser-induced fluorescence and UV detection of derivatized aldehydes in air samples using capillary electrophoresis

In this work, two capillary zone electrophoresis methodologies using UV absorption detection (214 nm) and laser-induced fluorescence detection (He/Cd laser, 325 nm excitation, 520 nm emission) of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde and acrolein) derivatized with dansylhydrazine (DNSH, 5-dimethylaminonaphthalene-1-sulfohydrazide) were proposed and validated. The aldehydes react with DNSH to form negatively charged molecules in methanolic medium. In both methodologies, nine DNSH-derivatives, including isomers of acetaldehyde, propionaldehyde and acrolein and two impurities were baseline separated in 20 mmol l(-1) phosphate buffer at pH 7.02, in less than 9 min. The limits of detection for the UV and LIF methodologies ranged from 1.1-9.5 microg l(-1) and 0.29-5.3 microg l(-1), respectively. The applicability of both methodologies to contemplate real samples was confirmed in the analysis of aldehyde-DNSH derivatives in indoor and outdoor air samples.

Quantitative time-resolved monitoring of nitrate formation in sea salt particles using a CCSEM/EDX single particle analysis

Progress of the nitrate formation in individual sea salt particles was detected as a function of time using aerosol samples collected during the TexAQS 2080 experiment We demonstrate that the time-resolved collection approach coupled with the automated EDX single particle analysis made it possible to follow in detail the time evolution of sea salt particles within a diverse aerosol mixture. Using a custom built Time-Resolved Aerosol Collector (TRAC), particulate samples were taken sequentially on grid-supported 50 nm carbon films with a time resolution of 10 min between two consecutive samples. The samples were analyzed in the laboratory using Computer Controlled Scanning Electron Microscopy with Energy-Dispersed analysis of X-rays (CCSEM/EDX). Between midnight of 08/16/00 and the early morning of 08/17/00, a steady, particularly sea salt rich aerosol was observed at the measurement site, which later showed the effects of atmospheric processing. During the night of 08/17/00 the sea salt particles were almost unprocessed, having elemental composition close to that of seawater. By 12 noon, the evolving atmosphere was able to completely convert them, predominantly to sodium nitrate particles. During the next night this process had nearly stopped and fairly virgin sea salt particles appeared again.

Formation and decomposition of hazardous chemical components contained in atmospheric aerosol particles

Air particulate matter contains a wide range of substances, some of which pose a threat to human health. Chemical reactions occurring on aerosol particles in the atmosphere can transform hazardous components and increase or decrease their potential for adverse health effects. Especially organic compounds react readily with atmospheric oxidants, and since fine aerosol particles have a high surface-to-volume ratio, their chemical composition can be efficiently changed by interaction with trace gases such as ozone and nitrogen oxides. In this paper the concepts required to understand and describe the formation and decomposition of hazardous chemical components contained in atmospheric aerosol particles are outlined. The processes at work on a molecular level in the chemical transformation of atmospheric particle components are illustrated for soot and polycyclic aromatic compounds (PACs), in particular for benzo[a]pyrene (BaP) which is one of the most prominent hazardous pollutants in the class of polycyclic aromatic hydrocarbons (PAHs). Recent results on the reaction kinetics and mechanisms of BaP degradation by ozone and nitrogen dioxide are presented. These results indicate faster degradation by atmospheric oxidants than previously estimated, which implies a higher potential for sampling artifacts and underestimation of the actual atmospheric abundance of BaP and other PAHs. Thus human exposure close to the sources of these compounds such as busy roadways may be significantly higher than previously assumed.

An analysis of factors that influence personal exposure to nitrogen oxides in residents of Richmond, Virginia

Nitrogen oxides (NO(x)) are ubiquitous pollutants in outdoor and indoor air. However, epidemiologic studies that evaluate health effects associated with NO(x) commonly rely upon outdoor concentrations of NO(x), nitrogen dioxide (NO(2)), or residence characteristics as surrogates for personal exposure. In this study, personal exposures (48 h) and corresponding indoor and outdoor concentrations of nitric oxide (NO), NO(2), and NO(x) were measured (July-September) in 39 adults and 9 children from 23 households in Richmond, Virginia, using Ogawa passive NO(x) monitors. Demographic, time-activity patterns, and household data were collected by questionnaire and used to develop exposure prediction models. Adults had higher NO(2), NO, and NO(x) exposures (means: 16, 63, and 79 ppb, respectively) than children (13, 49, and 62 ppb). Measurements taken in bedrooms (18, 57, and 75 ppb) and living rooms (19, 65, and 84 ppb) surpassed measurements taken outdoors (15, 21, and 36 ppb). In indoor locations, NO(x) concentrations were influenced largely by NO, and consequently, personal exposure prediction models for NO(x) were reflective of models for NO. Statistical models that best predicted personal exposures included indoor measurements; outdoor measurements contributed relatively little to personal exposure. Close to 70% of the variation in personal NO(2) and NO(x) exposure was explained by two variable models (bedroom NO(2) and time spent in other indoor locations; bedroom NO(x) and time spent in kitchen). Given appropriate resources, measurement error in epidemiologic studies can be reduced significantly with the use of personal exposure measurements or prediction models developed from indoor measurements and survey data.

Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed and relocated in the environment as a result of the incomplete combustion of organic matter. Many PAHs and their epoxides are highly toxic, mutagenic and/or carcinogenic to microorganisms as well as to higher systems including humans. Although various physicochemical methods have been used to remove these compounds from our environment, they have many limitations. Xenobiotic-degrading microorganisms have tremendous potential for bioremediation but new modifications are required to make such microorganisms effective and efficient in removing these compounds, which were once thought to be recalcitrant. Metabolic engineering might help to improve the efficiency of degradation of toxic compounds by microorganisms. However, efficiency of naturally occurring microorganisms for field bioremediation could be significantly improved by optimizing certain factors such as bioavailability, adsorption and mass transfer. Chemotaxis could also have an important role in enhancing biodegradation of pollutants. Here, we discuss the problems of PAH pollution and PAH degradation, and relevant bioremediation efforts.

Ozone effects on Sphagnum mosses, carbon dioxide exchange and methane emission in boreal peatland microcosms

Microcosms of a boreal peatland originating from an oligotrophic fen in Eastern Finland were fumigated under four ozone concentrations (0, 50, 100 and 150 ppb O3) in laboratory growth chambers during two separate experiments (autumn and summer) for 4 and 6 weeks, respectively. Ozone effects on Sphagnum mosses and the fluxes of carbon dioxide and methane were evaluated. In both experiments, the three Sphagnum species studied showed only a few significant responses to ozone. In the autumn experiment, membrane permeability of S. angustifolium, measured as conductivity and magnesium leakage, was significantly higher under ozone fumigation (P = 0.005 and < 0.001, respectively), and there was a distinct dose-dependence. S. magellanicum showed no clear responses, either for membrane leakage or pigment content. There were no substantial ozone responses in the gross photosynthesis or net CO2 exchange during the 6-week-long summer experiment, but dark ecosystem respiration was transiently increased by ozone concentration of 100 ppb after 14 days of exposure (P < 0.05). Fumigation with 100 ppb of ozone, however, more than doubled (P < 0.05) methane emission from the peatland monoliths. Our results suggest that increasing tropospheric ozone concentration may cause substantial changes in the carbon gas cycling of boreal peatlands, even though these changes are not closely associated with the changes in Sphagnum vegetation.

The surface charge of visible particulate matter predicts biological activation in human bronchial epithelial cells

The physicochemical complexity of airborne particulate matter (PM) has hampered identifying a specific mechanism(s) for its toxicity. In this study, selected physicochemical characteristics (i.e., size, particle number, acidity, and surface charge) were measured on various field PM, derived from urban ambient (St. Louis, Ottawa, Canada), residential (Woodstove), volcanic dust from Mt. St. Helen (MSH), and industrial [oil fly ash (OFA) coal fly ash (CFA)] sources. Morphometric analysis of visible (< or = 2.0 to >10 microm) field particles indicated that the industrial PM (OFA, CFA) had the smallest diameter and lowest total number of particles per weight while Woodstove and Ottawa had the largest diameter and highest number of particles. All PM lowered the pH of an unbuffered 10 mM NaCl solution from pH 7.4 to pH 4.7-6.8 but did not change the neutral pH of the cell culture medium, keratinocyte growth media (KGM). The surface charge (i.e., zeta potential) of microscopically visible (> or = 2.0 microm) field particles, suspended in either a Hepes-buffered KCl solution or in KGM, was measured by microelectrophoresis. In KCl solution, the mean zeta potential of all tested PM ranged from -36 +/- 2 (Woodstove) to -27 +/- 4.3 mV (MSH). When measured in KGM medium, the mean zeta potential value of each PM was significantly less (p > 0.001) than those measured in KCl solution, with values ranging from -17 +/- 0.3 mV (St. Louis) to -9 +/- 0.6 mV (MSH). Suspensions of field PM, its soluble and washed particulate fractions, were next prepared from each PM. The biological effects (i.e., increases in intracellular calcium ([Ca2+]i), cytokine release) of their exposure were measured in human, immortalized, tracheal-bronchial epithelial cells (BEAS-2B). Exposure of BEAS-2B cells to each fraction produced an immediate, but differential increase in [Ca2+]i and the subsequent release of the inflammatory cytokine IL-6, 4 and 16 h later. Increases in [Ca2+]i by field PM significantly correlated with the IL-6 released by each fraction (r2 > or = 0.76) after both 4 and 16 h exposures. The biological effects of each PM were compared with their physicochemical characteristics. No correlation was found between increases in [Ca2+]i or cytokine release and a PM's acidity or the number or size of its visible (> or = 2.0 microm) particles. However, the surface charge of PM field particles, when measured in the KGM exposure medium, showed a high correlation (r2 > or = 0.94) with the IL-6 release by field PM after both 4 and 16 h exposure. Increases in [Ca2+]i also correlated (r2 = 0.85) with the surface charge of PM field particles when measured in KGM. These data indicate that the surface charge (i.e., zeta potential) carried on PM's visible field particles predicts their differential release of the inflammatory cytokine IL-6 in cultures of human respiratory epithelial cells.

Neurogenic inflammation and particulate matter (PM) air pollutants

Exposure to a class of airborne pollutants known as particulate matter (PM) is an environmental health risk of global proportions. PM is thought to initiate and/or exacerbate respiratory disorders, such as asthma and airway hyper-responsiveness and is epidemiologically associated with causing death in the elderly and those with pre-existing respiratory, or cardiopulmonary disease. Plausible mechanisms of action to explain PM inflammation and its susceptible sub-population component are lacking. This review describes a series of published studies which indicate that PM initiates airway inflammation through sensory neural pathways, specifically by activation of capsaicin-sensitive vanilloid (e.g. VRI) irritant receptors. These acid-sensitive receptors are located on the sensory C nerve fibers that innervate the airways as well as on various immune and non-immune airway target cells. The activation of these receptors results in the release of neuropeptides from the sensory terminals that innervate the airways. Their interactions with airway target cells, result in signs of inflammation (e.g. bronchoconstriction, vasodilation, histamine release, mucous secretion etc.). Our data have linked the activation of the VR1 receptors to the surface charge carried on the colloidal particulates which constitute PM pollution. Related studies have examined how genetic and non-genetic factors modify the sensitivity of these irritant receptors and enhance the inflammatory responsiveness to PM. In summary, this review proposes a mechanism by which neurogenic elements initiate and sustain PM-mediated airway inflammation. Although neurogenic influences have been appreciated in normal airway homeostasis, they have not, until now, been associated with PM toxicity. The sensitivity of the sensory nervous system to irritants and its interactions with pulmonary target tissues, should encourage neuroscientists to explore the relevance of neurogenic influences to toxic disorders involving other peripheral target systems.

Negative-ion photoelectron spectroscopy, gas-phase acidity, and thermochemistry of the peroxyl radicals CH(3)OO and CH(3)CH(2)OO

Methyl, methyl-d(3), and ethyl hydroperoxide anions (CH(3)OO(-), CD(3)OO(-), and CH(3)CH(2)OO(-)) have been prepared by deprotonation of their respective hydroperoxides in a stream of helium buffer gas. Photodetachment with 364 nm (3.408 eV) radiation was used to measure the adiabatic electron affinities: EA[CH(3)OO, X(2)A' '] = 1.161 +/- 0.005 eV, EA[CD(3)OO, X(2)A' '] = 1.154 +/- 0.004 eV, and EA[CH(3)CH(2)OO, X(2)A' '] = 1.186 +/- 0.004 eV. The photoelectron spectra yield values for the term energies: Delta E(X(2)A' '-A (2)A')[CH(3)OO] = 0.914 +/- 0.005 eV, Delta E(X(2)A' '-A (2)A')[CD(3)OO] = 0.913 +/- 0.004 eV, and Delta E(X(2)A' '-A (2)A')[CH(3)CH(2)OO] = 0.938 +/- 0.004 eV. A localized RO-O stretching mode was observed near 1100 cm(-1) for the ground state of all three radicals, and low-frequency R-O-O bending modes are also reported. Proton-transfer kinetics of the hydroperoxides have been measured in a tandem flowing afterglow-selected ion flow tube (FA-SIFT) to determine the gas-phase acidity of the parent hydroperoxides: Delta(acid)G(298)(CH(3)OOH) = 367.6 +/- 0.7 kcal mol(-1), Delta(acid)G(298)(CD(3)OOH) = 367.9 +/- 0.9 kcal mol(-1), and Delta(acid)G(298)(CH(3)CH(2)OOH) = 363.9 +/- 2.0 kcal mol(-1). From these acidities we have derived the enthalpies of deprotonation: Delta(acid)H(298)(CH(3)OOH) = 374.6 +/- 1.0 kcal mol(-1), Delta(acid)H(298)(CD(3)OOH) = 374.9 +/- 1.1 kcal mol(-1), and Delta(acid)H(298)(CH(3)CH(2)OOH) = 371.0 +/- 2.2 kcal mol(-1). Use of the negative-ion acidity/EA cycle provides the ROO-H bond enthalpies: DH(298)(CH(3)OO-H) = 87.8 +/- 1.0 kcal mol(-1), DH(298)(CD(3)OO-H) = 87.9 +/- 1.1 kcal mol(-1), and DH(298)(CH(3)CH(2)OO-H) = 84.8 +/- 2.2 kcal mol(-1). We review the thermochemistry of the peroxyl radicals, CH(3)OO and CH(3)CH(2)OO. Using experimental bond enthalpies, DH(298)(ROO-H), and CBS/APNO ab initio electronic structure calculations for the energies of the corresponding hydroperoxides, we derive the heats of formation of the peroxyl radicals. The "electron affinity/acidity/CBS" cycle yields Delta(f)H(298)[CH(3)OO] = 4.8 +/- 1.2 kcal mol(-1) and Delta(f)H(298)[CH(3)CH(2)OO] = -6.8 +/- 2.3 kcal mol(-1).

DNA adduct formation by the ubiquitous environmental contaminant 3-nitrobenzanthrone in rats determined by (32)P-postlabeling

Diesel exhaust is known to induce tumors in animals and is suspected of being carcinogenic in humans. Of the compounds found in diesel exhaust and in airborne particulate matter, 3-nitrobenzanthrone (3-NBA), is a particularly powerful mutagen. We investigated the capacity of 3-NBA to form DNA adducts in vivo that could be used as agent-specific biomarkers of exposure. Female Sprague-Dawley rats were treated orally with 2 mg/kg body weight of 3-NBA, and DNA from various organs was analyzed by (32)P-postlabeling. High levels of 3-NBA-specific adducts were detectable in all organs. Both enrichment versions nuclease P1 digestion and n-butanol extraction resulted in patterns consisting of either 3 or 4 adducts remarkably similar in all tissues examined. The highest level of DNA adducts was found in the small intestine (38 adducts per 10(8) nucleotides) followed by forestomach, glandular stomach, kidney, liver, lung and bladder. To provide information on the nature of the adducts formed in vivo in rats, DNA adducts were cochromatographed in 2 independent systems with standardized deoxyguanosine adducts and deoxyadenosine adducts produced by reaction of 3-NBA in the presence of xanthine oxidase with deoxyribonucleoside 3'-monophosphates in vitro. In both systems, each of the rat adducts comigrated either with a deoxyguanosine or a deoxyadenosine-derived 3-NBA adduct. Our results demonstrate that 3-NBA binds covalently to DNA after metabolic activation, forming multiple DNA adducts in vivo, all of which are products derived from reductive metabolites bound to the purine bases (deoxyguanosine 60% and deoxyadenosine 40%).

Serum clara cell protein: a sensitive biomarker of increased lung epithelium permeability caused by ambient ozone

Ozone in ambient air may cause various effects on human health, including decreased lung function, asthma exacerbation, and even premature mortality. These effects have been evidenced using various clinical indicators that, although sensitive, do not specifically evaluate the O(3)-increased lung epithelium permeability. In the present study, we assessed the acute effects of ambient O(3) on the pulmonary epithelium by a new approach relying on the assay in serum of the lung-specific Clara cell protein (CC16 or CC10). We applied this test to cyclists who exercised for 2 hr during episodes of photochemical smog and found that O(3) induces an early leakage of lung Clara cell protein. The protein levels increased significantly into the serum from exposure levels as low as 0.060-0.084 ppm. Our findings, confirmed in mice exposed to the current U.S. National Ambient Air Quality Standards for O(3) (0.08 ppm for 8 hr) indicate that above the present natural background levels, there is almost no safety margin for the effects of ambient O(3) on airway permeability. The assay of CC16 in the serum represents a new sensitive noninvasive test allowing the detection of early effects of ambient O(3) on the lung epithelial barrier.

DNA adduct formation from the mutagenic air pollutant 3-nitrobenzanthrone

The environmental contaminant 3-nitrobenzanthrone (3-nitro-7H-benz[d, e]anthracen-7-one) was recently shown to be a very strong bacterial mutagen, suggesting a new class of mutagenic compounds present in airborne particulate matter and diesel exhaust. Using the 32P-postlabeling assay, we investigated the capacity for 3-nitrobenzanthrone to form DNA adducts in vitro. Calf thymus DNA was incubated with 3-nitrobenzanthrone and either xanthine oxidase, a mammalian nitroreductase or rat liver S9 or zinc. Under these conditions 3-nitrobenzanthrone formed a total of seven adducts detectable by 32P-postlabeling. Using enrichment by butanol extraction the highest level of DNA adduct formation was found with activation by zinc (RAL: 88.4+/-32 per 108 nucleotides) followed by activation with xanthine oxidase (RAL: 75.5+/-12) and activation by rat liver S9 (RAL: 48.6+/-8). Three of the seven adduct spots were detected in all activation systems, however different amounts of individual spots were obtained in the different in vitro systems. The adduct pattern observed for the enzymatic incubations consisted of three major spots and was essentially identical. Chemical reduction of 3-nitrobenzanthrone by zinc resulted in five adduct spots whose formation was found to be concentration dependent. All adducts of 3-nitrobenzanthrone observed in this study migrated primarily along a diagonal zone, typical for DNA adducts derived from extracts of airborne particulate matter. When butanol enrichment was compared with nuclease P1 enrichment one adduct was clearly sensitive to the 3'-monophosphatase activity of nuclease P1. Our results demonstrate that 3-nitrobenzanthrone binds covalently to DNA after metabolic activation, forming multiple DNA adducts in vitro all of which are reduction products. These adducts may contribute to the known genotoxicity and carcinogenicity of extracts from airborne particulates.

The impact of aerosols on solar ultraviolet radiation and photochemical smog

Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.