Co-occurrence of extremes in surface ozone, particulate matter, and temperature over eastern North America

Heat waves and air pollution episodes pose a serious threat to human health and may worsen under future climate change. In this paper, we use 15 years (1999-2013) of commensurately gridded (1° x 1°) surface observations of extended summer (April-September) surface ozone (O3), fine particulate matter (PM2.5), and maximum temperature (TX) over the eastern United States and Canada to construct a climatology of the coincidence, overlap, and lag in space and time of their extremes. Extremes of each quantity are defined climatologically at each grid cell as the 50 d with the highest values in three 5-y windows (∼95th percentile). Any two extremes occur on the same day in the same grid cell more than 50% of the time in the northeastern United States, but on a domain average, co-occurrence is approximately 30%. Although not exactly co-occurring, many of these extremes show connectedness with consistent offsets in space and in time, which often defy traditional mechanistic explanations. All three extremes occur primarily in large-scale, multiday, spatially connected episodes with scales of >1,000 km and clearly coincide with large-scale meteorological features. The largest, longest-lived episodes have the highest incidence of co-occurrence and contain extreme values well above their local 95th percentile threshold, by +7 ppb for O3, +6 µg m-3 for PM2.5, and +1.7 °C for TX. Our results demonstrate the need to evaluate these extremes as synergistic costressors to accurately quantify their impacts on human health.

Ozone concentration in the ground atmosphere and morbidity during extreme heat in the summer of 2010

Dependence of the population morbidity on the ground-level ozone concentration in the summer of 2010 was studied in a city with low urbanization (Vyatskie Polyany, Kirov oblast) and in Moscow. At a high air temperature and low ozone concentration, the population morbidity was not associated with these parameters in Vyatskie Polyany. When the average daily ground-level ozone concentration exceeded 60 μg/m³ for 13 successive days, the correlation coefficient between ozone concentration and the number of ambulance calls was statistically significant, r = 0.62. Heavy smoke from forest fires reduced ozone concentration, and the number of emergency calls did not increase. In Moscow, the incidence of respiratory diseases and population mortality were growing up at high ozone concentrations.

Gas-phase advanced oxidation for effective, efficient in situ control of pollution

In this article, gas-phase advanced oxidation, a new method for pollution control building on the photo-oxidation and particle formation chemistry occurring in the atmosphere, is introduced and characterized. The process uses ozone and UV-C light to produce in situ radicals to oxidize pollution, generating particles that are removed by a filter; ozone is removed using a MnO2 honeycomb catalyst. This combination of in situ processes removes a wide range of pollutants with a comparatively low specific energy input. Two proof-of-concept devices were built to test and optimize the process. The laboratory prototype was built of standard ventilation duct and could treat up to 850 m(3)/h. A portable continuous-flow prototype built in an aluminum flight case was able to treat 46 m(3)/h. Removal efficiencies of >95% were observed for propane, cyclohexane, benzene, isoprene, aerosol particle mass, and ozone for concentrations in the range of 0.4-6 ppm and exposure times up to 0.5 min. The laboratory prototype generated a OH(•) concentration derived from propane reaction of (2.5 ± 0.3) × 10(10) cm(-3) at a specific energy input of 3 kJ/m(3), and the portable device generated (4.6 ± 0.4) × 10(9) cm(-3) at 10 kJ/m(3). Based on these results, in situ gas-phase advanced oxidation is a viable control strategy for most volatile organic compounds, specifically those with a OH(•) reaction rate higher than ca. 5 × 10(-13) cm(3)/s. Gas-phase advanced oxidation is able to remove compounds that react with OH and to control ozone and total particulate mass. Secondary pollution including formaldehyde and ultrafine particles might be generated, depending on the composition of the primary pollution.

BioArena system for knowing and understanding the biological world: a review with new experimental results

A simple observation is the basis of the development of BioArena system: according to the first observations during the biological incubation after inoculation there is formaldehyde (HCHO) emission from the chromatographic spots; in this emission process, the level of HCHO molecules decreases time dependently. In fact, the antibiotic effect of an antibiotic-like compound decreases in parallel with the HCHO emission. The investigations demonstrated clearly a unique function and role of endogenous HCHO and its one main reaction product, ozone (O3), in the antiproliferative (e.g., antimicrobial) effect of different molecules with diverse chemical structures. The results in BioArena can be extended for in vivo conditions (e.g., greenhouse experiments), as well. For the pretreatment with different doses of inducers (immunostimulation-inducing molecules) there are always four bioequivalent immunostimulating response ranges (quadruple bioequivalent immune response system) in plants. The inducers (e.g., N-methylated basic amino acids, salicylic acid, cinnamic acid, and trace elements) do not participate directly in the induction of the immunostimulating effect. These new findings support a statement that HCHO and its reaction products (mainly O3), as bioreactive small molecules, are responsible for the immunostimulating activity (in vivo conditions), as well.

Impact of physical properties on ozone removal by several porous materials

Models of reactive uptake of ozone in indoor environments generally describe materials through aerial (horizontal) projections of surface area, a potentially limiting assumption for porous materials. We investigated the effect of changing porosity/pore size, material thickness, and chamber fluid mechanic conditions on the reactive uptake of ozone to five materials: two cellulose filter papers, two cementitious materials, and an activated carbon cloth. Results include (1) material porosity and pore size distributions, (2) effective diffusion coefficients for ozone in materials, and (3) material-ozone deposition velocities and reaction probabilities. At small length scales (0.02-0.16 cm) increasing thickness caused increases in estimated reaction probabilities from 1 × 10(-6) to 5 × 10(-6) for one type of filter paper and from 1 × 10(-6) to 1 × 10(-5) for a second type of filter paper, an effect not observed for materials tested at larger thicknesses. For high porosity materials, increasing chamber transport-limited deposition velocities resulted in increases in reaction probabilities by factors of 1.4-2.0. The impact of physical properties and transport effects on values of the Thiele modulus, ranging across all materials from 0.03 to 13, is discussed in terms of the challenges in estimating reaction probabilities to porous materials in scenarios relevant to indoor environments.

Long-term performance of passive materials for removal of ozone from indoor air

The health effects associated with exposure to ozone range from respiratory irritation to increased mortality. In this paper, we explore the use of three green building materials and an activated carbon (AC) mat that remove ozone from indoor air. We studied the effects of long-term exposure of these materials to real environments on ozone removal capability and pre- and post-ozonation emissions. A field study was completed over a 6-month period, and laboratory testing was intermittently conducted on material samples retrieved from the field. The results show sustained ozone removal for all materials except recycled carpet, with greatest ozone deposition velocity for AC mat (2.5-3.8 m/h) and perlite-based ceiling tile (2.2-3.2 m/h). Carbonyl emission rates were low for AC across all field sites. Painted gypsum wallboard and perlite-based ceiling tile had similar overall emission rates over the 6-month period, while carpet had large initial emission rates of undesirable by-products that decayed rapidly but remained high compared with other materials. This study confirms that AC mats and perlite-based ceiling tile are viable surfaces for inclusion in buildings to remove ozone without generating undesirable by-products. PRACTICAL IMPLICATIONS The use of passive removal materials for ozone control could decrease the need for, or even render unnecessary, active but energy consuming control solutions. In buildings where ozone should be controlled (high outdoor ozone concentrations, sensitive populations), materials specifically designed or selected for removing ozone could be implemented, as long as ozone removal is not associated with large emissions of harmful by-products. We find that activated carbon mats and perlite-based ceiling tiles can provide substantial, long-lasting, ozone control.

Photochemical modeling in California with two chemical mechanisms: model intercomparison and response to emission reductions

An updated version of the Statewide Air Pollution Research Center (SAPRC) chemical mechanism (SAPRC07C) was implemented into the Community Multiscale Air Quality (CMAQ) version 4.6. CMAQ simulations using SAPRC07C and the previously released version, SAPRC99, were performed and compared for an episode during July-August, 2000. Ozone (O3) predictions of the SAPRC07C simulation are generally lower than those of the SAPRC99 simulation in the key areas of central and southern California, especially in areas where modeled concentrations are greater than the federal 8-hr O3 standard of 75 parts per billion (ppb) and/or when the volatile organic compound (VOC)/nitrogen oxides (NOx) ratio is less than 13. The relative changes of ozone production efficiency (OPE) against the VOC/NOx ratio at 46 sites indicate that the OPE is reduced in SAPRC07C compared with SAPRC99 at most sites by as much as approximately 22%. The SAPRC99 and SAPRC07C mechanisms respond similarly to 20% reductions in anthropogenic VOC emissions. The response of the mechanisms to 20% NOx emissions reductions can be grouped into three cases. In case 1, in which both mechanisms show a decrease in daily maximum 8-hr O3 concentration with decreasing NOx emissions, the O3 decrease in SAPRC07C is smaller. In case 2, in which both mechanisms show an increase in O3 with decreasing NOx emissions, the O3 increase is larger in SAPRC07C. In case 3, SAPRC07C simulates an increase in O3 in response to reduced NOx emissions whereas SAPRC99 simulates a decrease in O3 for the same region. As a result, the areas where NOx controls would be disbeneficial are spatially expanded in SAPRC07C. Although the results presented here are valuable for understanding differences in predictions and model response for SAPRC99 and SAPRC07C, the study did not evaluate the impact of mechanism differences in the context of the U.S. Environmental Protection Agency's guidance for using numerical models in demonstrating air quality attainment. Therefore, additional study is required to evaluate the full regulatory implications of upgrading air quality models to SAPRC07.

Squalene and cholesterol in dust from danish homes and daycare centers

Given the rate at which humans shed their skin (desquamation), skin flakes that contain squalene and cholesterol are anticipated to be major constituents of indoor dust. These compounds have been detected in more than 97% of the dust samples collected from 500 bedrooms and 151 daycare centers of young children living in Odense, Denmark. The mass fractions of squalene in dust were approximately log-normally distributed (homes: GM = 32 μg/g, GSD = 4.3; daycare centers: GM = 11.5 μg/g, GSD = 4.3); those of cholesterol displayed a poorer fit to such a distribution (homes: GM = 625 μg/g, GSD = 3.4; daycare centers: GM = 220 μg/g, GSD = 4.0). Correlations between squalene and cholesterol were weak (r = 0.22). Furthermore, the median squalene-to-cholesterol ratio in dust (~0.05) was more than an order of magnitude smaller than that in skin oil. This implies sources in addition to desquamation (e.g., cholesterol from cooking) coupled, perhaps, with a shorter indoor lifetime for squalene. Estimated values of squalene's vapor pressure, while uncertain, suggest meaningful redistribution from dust to other indoor compartments. We estimate that dust containing squalene at 60 μg/g would contribute about 4% to overall ozone removal by indoor surfaces. This is roughly comparable to the fraction of ozone removal that can be ascribed to reactions with indoor terpenes. Squalene containing dust is anticipated to contribute to the scavenging of ozone in all settings occupied by humans.

RO filtration of biologically treated textile and dyeing effluents using ozonation as a pre-treatment

Bench-scale experiments were conducted to investigate the application of ozonation pre-treatment for biologically treated textile and dyeing wastewater to improve performance of the RO process. Based on ozonation experiments, four specific ozone consumptions (SOC), 0, 0.3, 0.6, 4.0 mg O₃/mg DOC₀ were chosen for study of the effects of ozonation on the reverse osmosis (RO) process. Membrane flux was recorded. Also, the permeate water quality parameters such as TOC, conductivity were analyzed. In addition, fouled membrane cleaning was studied. The study further examined the nature and mechanisms of membrane fouling using scanning electron microscopy (SEM) and the energy dispersive X-ray spectrometer (EDS). The effect of ozonation on RO filtration was found to depend on SOC. The study revealed that significant improvement can be achieved in the efficiency of RO filtration by employing ozonation with 0.6 mg O₃/mg DOC₀ SOC. Although the product water purity slightly decreased, the ozonation pre-treatment showed advantages at 0.6 mg O₃/mg DOC₀ SOC for the following: (i) mitigation of flux decline due to membrane fouling; (ii) improvement in foulants cleanability. In addition, hypotheses were put forward to explain the reasons from the aspect of organic matter characteristics changed by ozonation, such as changing on functional groups and molecular weight of organic matter.

Feasibility of ozone absorption by H2O2 solution in rotating packed beds

This work examined the feasibility of ozone (O(3)) absorption by H(2)O(2) solution in a rotating packed bed (RPB). The O(3) removal efficiency was determined at various operating variables including RPB speed, gas flow rate, and liquid flow rate in three RPBs. For each RPB, the results demonstrated that the RPB speed positively affected the O(3) removal efficiency. Also, the O(3) removal efficiency increased with the liquid flow rate but decreased with the gas flow rate. Moreover, the obtained results indicated that the O(3) removal efficiency increased as the inner radius of the bed was increased and the outer radius of the bed was decreased. Furthermore, the developed method for O(3) absorption using H(2)O(2) solution could provide the removal efficiency of more than 95%. Consequently, the novel method would have a great potential in the removal of O(3) from the exhausted gases.

Elimination of volatile organic compounds by biofiltration: a review

Volatile organic compounds (VOCs) are pollutants that are responsible for the formation of the tropospheric ozone, one of the precursors of smog. VOCs are emitted by various industries including chemical plants, pulp and paper mills, pharmaceuticals, cosmetics, electronics and agri-food industries. Some VOCs cause odor pollution while many of them are harmful to environment and human or animal health. For the removal of VOCs, biofiltration, a biological process, has proved to be reliable when properly operated. This process has therefore been widely applied in Europe and North America. The main advantages associated with the use of biofiltration are related to its set-up, maintenance, and operating costs which are usually lower than those related to other VOCs control technologies and because it is less harmful for the environment than conventional processes like incineration. In the present paper, the main parameters (type, moisture, pH, and temperature of filter bed, microbial population, nutrients concentrations, and VOCs' inlet load) to be controlled during the biofiltration are identified and described in detail. The main phenomena involved in biofiltration are also discussed. For improving the efficiency of VOC control biotechnology, new techniques are now proposed that include the use of membranes, biphasic reactors, UV photolysis, and many others.

Inactivation of particle-associated microorganisms in wastewater disinfection: modeling of ozone and chlorine reactive diffusive transport in polydispersed suspensions

Occlusion of microorganisms in wastewater particles often governs the overall performance of a disinfection system, and the associated health risks of post-disinfected effluents. Little is currently known on the penetration of chemical oxidants into particles developed in wastewater treatment. In this work, a reactive transport model that incorporates intra- and extra-particle chemical decay, radial intra-particle diffusion, mass transfer resistance at particle surfaces, and non-linear reaction kinetics within a competitive multi-particle size aqueous environment, was used to analyze the penetration of ozone and chlorine into wastewater particles. Individual characteristics from two secondary wastewater treatment facilities were used in model calibration. Simulations revealed that significant ozone transport within particles greater than 6 microm required large initial concentrations to exhaust the preferential reaction with aqueous soluble matter. Chlorinated samples exhibited apparently slower reactions and thus deeper penetration (22-40 microm). Chlorine penetration was less sensitive to variations in the extra-particle reaction and disinfectant concentration than ozone. Model simulations that considered elevated initial concentrations of chemical disinfectants revealed that complete inactivation of all particle size domains was not possible with current disinfection practices (e.g., contact times). Reduction in the health risks associated with wastewater particles requires treatment that efficiently balances particle removal (filtration) and particle inactivation (disinfection).

Elimination of laboratory ozone leads to a dramatic improvement in the reproducibility of microarray gene expression measurements

Background

Environmental ozone can rapidly degrade cyanine 5 (Cy5), a fluorescent dye commonly used in microarray gene expression studies. Cyanine 3 (Cy3) is much less affected by atmospheric ozone. Degradation of the Cy5 signal relative to the Cy3 signal in 2-color microarrays will adversely reduce the Cy5/Cy3 ratio resulting in unreliable microarray data.

Results

Ozone in central Arkansas typically ranges between ~22 ppb to ~46 ppb and can be as high as 60–100 ppb depending upon season, meteorological conditions, and time of day. These levels of ozone are common in many areas of the country during the summer. A carbon filter was installed in the laboratory air handling system to reduce ozone levels in the microarray laboratory. In addition, the airflow was balanced to prevent non-filtered air from entering the laboratory. These modifications reduced the ozone within the microarray laboratory to ~2–4 ppb. Data presented here document reductions in Cy5 signal on both in-house produced microarrays and commercial microarrays as a result of exposure to unfiltered air. Comparisons of identically hybridized microarrays exposed to either carbon-filtered or unfiltered air demonstrated the protective effect of carbon-filtration on microarray data as indicated by Cy5 and Cy3 intensities. LOWESS normalization of the data was not able to completely overcome the effect of ozone-induced reduction of Cy5 signal. Experiments were also conducted to examine the effects of high humidity on microarray quality. Modest, but significant, increases in Cy5 and Cy3 signal intensities were observed after 2 or 4 hours at 98–99% humidity compared to 42% humidity.

Conclusion

Simple installation of carbon filters in the laboratory air handling system resulted in low and consistent ozone levels. This allowed the accurate determination of gene expression by microarray using Cy5 and Cy3 fluorescent dyes.

Kinetics of the ozonation of muconic acid in water

The removal of muconic acid (specifically trans-trans-butanedioc acid) with ozone from water has been studied for kinetics purposes. Concentrations of muconic acid of 4.4x10(-4)M are completely removed with ozone in less than 14 and 9 min at pH 3 and 7, respectively, and 3x10(-4)M of ozone in the gas. The positive influence of pH was due to the more reactive muconic acid dissociated form with ozone. The process can be described as a second order irreversible gas-liquid reaction developing in the moderate kinetic regime of absorption. At the experimental conditions investigated no free radical reactions are present and muconic acid is entirely oxidized by molecular ozone. Rate constants of the direct reaction between muconic acid and ozone were found to be 1.6x10(4) and 1.4x10(5)M(-1)s(1) at 20 degrees C, pH 3 and 7, respectively, according to film theory.

Continuous extraction and destruction of chloro-organics in wastewater using ozone-loaded Volasiltrade mark245 solvent

Extracting waterborne contaminants to ozone-loaded Volasiltrade mark245 (a siloxane solvent in which ozone is ten times more soluble than water) has been studied as a means of enhancing reaction kinetics and thus, providing more rapid wastewater decontamination. Investigation was carried out with respect to 2-chlorophenol and dichloromethane. Using a pilot scale continuous flow liquid-liquid/ozone water treatment system, 2-chlorophenol was extracted to the ozone-loaded solvent phase and considerable extents of destruction were achieved. However, the approach was demonstrated to yield slightly less destruction than direct gas contact for the same utilization of ozone and enhanced reaction kinetics were not shown to occur. This was suggested to be due to increased interfacial mass transfer resistance and/or the promotion of less destructive reaction pathways. Modification of the existing pilot system, by conversion from co- to counter-current solvent-loading, enabled greater dissolved ozone concentrations to be achieved within the solvent. Increasing the counter-current exchange column height to approximately 2.5m was suggested for achieving a near optimum level of performance. The liquid-liquid/ozone approach was demonstrated to be an effective means of indirectly exposing wastewater contaminants to concentrated ozone. As such the technology may be applicable as an alternative to direct gas contact in instances where the avoidance of contaminant sparging is desired (i.e. where contaminants are highly volatile, pungent and/or toxic) or foaming occurs.

Decomposition of mixed malodorants in a wire-plate pulse corona reactor

Decomposition characteristics of two groups of representative mixed malodorants (1, ethanethiol + hydrogen sulfide; 2, ethanethiol + ammonia) in air were investigated employing a wire-plate pulse corona reactor. A new type of high-voltage pulse generator with a thyratron switch and a Blumlein pulse-forming network (BPFN) was used in our experiments. The experiments were conducted at a gas-flow rate of 13 m3/h. Important parameters, including peak voltage, chemical structures of malodorants, pulse frequency, and initial concentration, which influenced the removal efficiency, were investigated. The results showed that the mixed malodorants could be treated effectively by pulse corona. The removal efficiencies of 200 mg/m3 C2H5SH and 200 mg/m3 H2S for group 1 were 95.6% and 100%, respectively, which were almost equal to those of the two pollutants separately. The energy cost was about 65.1-81.4 J/L, which was 31.5-45.2% lower than for treating pollutants alone. The removal efficiencies of 105 mg/m3 C2HsSH and 40 mg/m3 NH3 for group 2 were 93.1% and almost 100%, and the energy cost was 65.1 J/L, 55.6% lower than that which was treated separately. In the case of two groups of mixed malodorants removal, NOx, 03, SO2, CO2, and CO were all observed. Moreover, some sulfur and white crystal ammonium nitrates were discovered adhering to the corona wires in the removal of groups 1 and 2, respectively. A dynamics model was developed to describe the relation of the removal efficiency with specific energy density and initial concentration. In the case of group 1 removal,the decomposition rate constants decreased as compared to the single treating. As for group 2 removal, the decomposition rate constants increased, especially for NH3. According to the results, the optimization design for the reactor and the matching of high pulse voltage source can be reckoned.

Management of tropospheric ozone by reducing methane emissions

Background concentrations of tropospheric ozone are increasing and are sensitive to methane emissions, yet methane mitigation is currently considered only for climate change. Methane control is shown here to be viable for ozone management. Identified global abatement measures can reduce approximately 10% of anthropogenic methane emissions at a cost-savings, decreasing surface ozone by 0.4-0.7 ppb. Methane controls produce ozone reductions that are widespread globally and are realized gradually (approximately 12 yr). In contrast, controls on nitrogen oxides (NOx) and nonmethane volatile organic compounds (NMVOCs) target high-ozone episodes in polluted regions and affect ozone rapidly but have a smaller climate benefit. A coarse estimate of the monetized global benefits of ozone reductions for agriculture, forestry, and human health (neglecting ozone mortality) justifies reducing approximately 17% of global anthropogenic methane emissions. If implemented, these controls would decrease ozone by -1 ppb and radiative forcing by approximately 0.12 W m(-2). We also find that climate-motivated methane reductions have air quality-related ancillary benefits comparable to those for CO2. Air quality planning should consider reducing methane emissions alongside NOx and NMVOCs, and because the benefits of methane controls are shared internationally, industrialized nations should consider emphasizing methane in the further development of climate change or ozone policies.

Ozonation of naphthalenesulphonic acid in the aqueous phase in the presence of basic activated carbons

The present study aimed to explore the possibility of increasing the purification efficacy of ozone in the removal of high-toxicity contaminants by using carbons of basic character and to analyze the mechanism involved in this process. These carbons were prepared by treating a commercial activated carbon (Witco, W) with ammonia (W-A), ammonium carbonate (W-C), or urea (W-U), under high pressure and temperature. The ammonia and carbonate treatments slightly increased the mesoporosity and, to a greater degree, the macroporosity of carbon W, whereas the urea treatment produced an increase in the porosity across the whole range of pore sizes. In addition, treatment of the activated carbon with these nitrogenating agents produced a marked change in the chemical nature of its surface. Thus, according to the pH of the point of zero charge (pHPZC) values obtained for each sample, carbon W was neutral (pHPZC = 7.12), but the treated carbons were basic, especially carbon W-U (pHPZC = 8.85). This basicity results from an increased concentration of basic oxygenated and nitrogenated surface functional groups, as confirmed by the results of elemental and XPS analyses. An increase in the degradation of 1,3,6-naphthalenetrisulfonic acid was observed when the activated carbon samples were added to the system. This degradation was especially enhanced in the presence of carbon W-U. The increased NTS degradation rate in the presence of the activated carbon is due to an increased concentration of highly reactive radicals in the system. When the catalytic activity of the activated carbon samples was related to their chemical and textural characteristics, it was found that: (i) The catalytic activity increased with an increase in the surface basicity. Interestingly, in the sample with greatest catalytic activity in NTS ozonation, carbon W-U, most of the nitrogenated surface groups introduced were pyrrol groups. These groups increase the electronic density of the basal plane of the activated carbon, thereby enhancing the reduction of ozone on the surface and the generation of highly reactive radicals in the system. (ii) The greater catalytic activity of carbon W-U may also be partly related to its greater surface area and higher volume of mesopores and macropores; these large pores facilitate access of the ozone to the surface active centers of the carbon, increasing its catalytic activity. The presence of the activated carbon samples during NTS ozonation also favored the removal of total organic carbon present in the solution, due to (a) transformation of organic matter into CO2 through the generation of highly reactive species catalyzed by the presence of the activated carbons (catalytic contribution) and (b) adsorption of NTS oxidation byproducts on the activated carbon (adsorptive contribution). The results obtained show that activated carbons treated with nitrogenating agents are very promising catalysts for application in the ozonation of aromatic compounds.

An operational assessment of the application of the relative reduction factors in the demonstration of attainment of the 8-hr ozone National Ambient Air Quality Standard

The U.S. Environmental Protection Agency in 1997 revised the 1-hr ozone (O3) National Ambient Air Quality Standard (NAAQS) to one based on an 8-hr average, resulting in potential nonattainment status for substantial portions of the eastern United States. The regulatory process provides for the development of a state implementation plan that includes a demonstration that the projected future O3 concentrations will be at or below the NAAQS based on photochemical modeling and analytical techniques. In this study, four photochemical modeling systems, based on two photochemical models, Community Model for Air Quality and the Comprehensive Air Quality Model with extensions, and two emissions processing models, Sparse Matrix Optimization Kernel for Emissions and Emissions Modeling System, were applied to the eastern United States, with emphasis on the northeastern Ozone Transport Region in terms of their response to oxides of nitrogen and volatile organic carbon-focused controls on the estimated design values. With the 8-hr O3 NAAQS set as a bright-line test, it was found that a given area could be termed as being in or out of attainment of the NAAQS depending upon the modeling system. This suggests the need to provide an estimate of model-to-model uncertainty in the relative reduction factor (RRF) for a better understanding of the uncertainty in projecting the status of an area's attainment. Results indicate that the model-to-model differences considered in this study introduce

Effect of substrate Henry's constant on biofilter performance

Butanol, ether, toluene, and hexane, which have Henry's constants ranging from 0.0005 to 53, were used to investigate the effects of substrate solubility or availability on the removal of volatile organic compounds (VOCs) in trickle-bed biofilters. Results from this study suggest that, although removal of a VOC generally increases with a decrease in its Henry's constant, an optimal Henry's constant range for biofiltration may exist. For the treatment of VOCs with high Henry's constant values, such as hexane and toluene, the transfer of VOCs between the vapor and liquid phases or between the vapor phase and the biofilm is a rate-determining step. However, oxygen (O2) transfer may become a rate-limiting step in treating VOCs with low Henry's constants, such as butanol, especially at high organic loadings. The results demonstrated that in a gas-phase aerobic biofilter, nitrate can serve both as a growth-controlling nutrient and as an electron acceptor in a biofilm for the respiration of VOCs with low Henry's constants. Microbial communities within the biofilters were examined using denaturing gradient gel electrophoresis to provide a more complete picture of the effect of O2 limitation and denitrification on biofilter performance.

Demonstrating attainment of the air quality standards: integration of observations and model predictions into the probabilistic framework

This paper introduces an integrated observational-modeling approach to transform the deterministic nature of attainment demonstrations of the National Ambient Air Quality Standard (NAAQS) into the probabilistic framework. While the methods presented here can be used to address any air quality standard that is based on extreme values, this paper focuses on the application to the 1-hr and 8-hr NAAQS for ozone. Extreme value statistics and resampling techniques are applied to estimate the probability of exceeding the NAAQS for both 1-hr and 8-hr ozone concentrations. Within the integrated observation-modeling analysis approach, we show that the model-to-model differences in the predicted responses to emission reductions are smaller than the model-to-model differences in predicted absolute ozone concentrations. We illustrate that the emission reductions stemming from a real-world emission control strategy would substantially reduce the probability of exceeding the NAAQS over a large portion of the eastern United States, especially for the 8-hr average ozone concentrations.

Oxidative damage to extracellular fluids by ozone and possible protective effects of thiols

Environmental levels of ozone (O3) frequently exceed air quality standards in many urban areas, and much research has been devoted to pathophysiological effects of O3 inhalation. Inhaled O3 will interact primarily with respiratory tract lining fluids (RTLF) and with constituents therein. It is believed that interaction of O3 with constituents in RTLF occurs by reactive absorption. We investigated interactions of O3 with human blood plasma, used as a model extracellular fluid representing RTLF, and studied oxidation of plasma antioxidants, proteins, and lipids. Plasma was exposed to various concentrations of O3 in humidified air, supplied at a continuous flow, in a system that mimics exposure of RTLF to inhaled O3 in vivo. Interaction of O3 with plasma appeared to be caused by reactive absorption of O3 by plasma. It was found that O3 reacts primarily with the aqueous antioxidants ascorbate and urate. Reactive absorption of O3 by plasma ascorbate and urate was found to be more efficient at low (2 ppm) O3 levels than at high (16 ppm) levels. We were also able to detect oxidative damage to plasma proteins and lipids after prolonged exposure to O3. Second, we investigated whether GSH or dihydrolipoic acid (DHLA) could prevent oxidative damage to plasma proteins and lipids by O3, under our exposure conditions. In contrast to plasma, RTLF contain relatively high amounts of GSH, which may contribute to antioxidant protection to respiratory tract epithelial cells. DHLA is an endogenous dithiol and has potent antioxidant properties. Addition of either GSH or DHLA to plasma (at concentrations up to 1 mM) prior to O3 exposure did not inhibit oxidation of plasma proteins and lipids during exposure to O3, nor did it attenuate depletion rates of ascorbate or urate. Our results indicate that added thiols cause increased reactive absorption of O3, rather than preventing reaction of O3 with other plasma constituents. Thiol supplementation could afford protection against O3-induced injury in vivo by increasing reactive absorption of O3 in the upper respiratory tract, thereby protecting the epithelia of lower airways and gas-exchanging portions of the lungs from exposure to toxic levels of O3.(ABSTRACT TRUNCATED AT 400 WORDS)

Ozone removal capability of a welding fume respirator containing activated charcoal

Development of air purifying respirators for protection against ozone has been slowed by concerns about oxidation of charcoal and other available sorbents. The suitability of a charcoal sorbent for low concentrations of ozone was evaluated as a part of the development of a half-mask air purifying respirator designed for welding fumes and ozone. Testing of the respirator confirmed that charcoal can be a suitable sorbent for low levels of ozone. Where the respirator is properly selected, fit tested, and worn, respirator use against welding fumes and ozone at concentrations not exceeding 10 times the permissible exposure limit had been recommended.