A counter-current parallel-plate membrane denuder for the non-specific removal of trace gases

Engine exhaust particulate and gas phase contributions to vascular toxicity

Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6 h/d × 50 d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions.

Soot aggregate restructuring due to coatings of secondary organic aerosol derived from aromatic precursors

Restructuring of monodisperse soot aggregates due to coatings of secondary organic aerosol (SOA) derived from hydroxyl radical-initiated oxidation of toluene, p-xylene, ethylbenzene, and benzene was investigated in a series of photo-oxidation (smog) chamber experiments. Soot aggregates were generated by combustion of ethylene using a McKenna burner, treated by denuding, size-selected by a differential mobility analyzer, and injected into a smog chamber, where they were exposed to low vapor pressure products of aromatic hydrocarbon oxidation, which formed SOA coatings. Aggregate restructuring began once a threshold coating mass was reached, and the degree of the subsequent restructuring increased with mass growth factor. Although significantly compacted, fully processed aggregates were not spherical, with a mass-mobility exponent of 2.78, so additional SOA was required to fill indentations between collapsed branches of the restructured aggregates before the dynamic shape factor of coated particles approached 1. Trends in diameter growth factor, effective density, and dynamic shape factor with increasing mass growth factor indicate distinct stages in soot aggregate processing by SOA coatings. The final degree and coating mass dependence of soot restructuring were found to be the same for SOA coatings from all four aromatic precursors, indicating that the surface tensions of the SOA coatings are similar.

Field performance evaluation during fog-dominated wintertime of a newly developed denuder-equipped PM1 sampler

This study presents the performance evaluation of a novel denuder-equipped PM1 (particles having aerodynamic diameter less than 1 μm) sampler, tested during fog-dominated wintertime, in the city of Kanpur, India. One PM1 sampler and one denuder-equipped PM1 sampler were co-located to collect ambient PM1 for 25 days. The mean PM1 mass concentration measured on foggy days with the PM1 sampler and the denuder-equipped PM1 sampler was found to be 165.95 and 135.48 μg/m(3), respectively. The mean PM1 mass concentration measured on clear days with the PM1 sampler and the denuder-equipped PM1 sampler was observed to be 159.66 and 125.14 μg/m(3), respectively. The mass concentration with denuder-fitted PM1 sampler for both foggy and clear days was always found less than the PM1 sampler. The same drift was observed in the concentrations of water-soluble ions and water-soluble organic carbon (WSOC). Moreover, it was observed that the use of denuder leads to a significant reduction in the PM positive artifact. The difference in the concentration of chemical species obtained by two samplers indicates that the PM1 sampler without denuder had overestimated the concentrations of chemical species in a worst-case scenario by almost 40 %. Denuder-fitted PM1 sampler can serve as a useful sampling tool in estimating the true values for nitrate, ammonium, potassium, sodium and WSOC present in the ambient PM.

Use of a versatile high efficiency multiparallel denuder for the sampling of PAHs in ambient air: gas and particle phase concentrations, particle size distribution and artifact formation

The design and performance of a multiparallel plate denuder able to operate at low and high-flow (3-30 L/min) for the collection of polycyclic aromatic hydrocarbon (PAH) vapor is described. The denuder, in combination with a micro orifice uniform deposit impactor (MOUDI) was used to assess processes of artifact formation in MOUDIs used with and without an upstream denuder. Duplicate sampling trains with an upstream denuder showed good repeatability of the measured gas and particle-phase concentrations and low breakthrough in the denuder (3.5-15%). The PAH size distributions within undenuded and denuded MOUDIs were studied. Use of the denuder altered the measured size distribution of PAHs toward smaller sizes, but both denuded and undenuded systems are subject to sampling artifacts.

Evaluation of a newly developed diffusion denuder for atmospheric aerosol separation from co-pollutant gases

This paper presents the design, development and performance evaluation of a non-selective membrane based single annular tube diffusion denuder employed to separate co-pollutant gases from the aerosol of interest. The experiments were carried out on a single annular tube diffusion denuder and the gas removal efficiencies were experimentally determined using a laboratory scale setup as well as under ambient conditions. Using a simple combustion source, the removal efficiency of carbon monoxide was calculated for different main flow (MF) and flush flow (FF) combinations and was found to be in the range of 94-100%. The overall soot particle transmission efficiency was found to be in the range of 70-99% for particle size between 0.3 μm and 2 μm. Overall, transmission efficiencies for submicron particles were also evaluated using an ultrafine condensation particle counter. After the controlled laboratory testing of the prototype denuder, experiments were conducted using ambient air as the test aerosol. This prototype denuder provided a much higher efficiency of gaseous removal in a single stage as compared to earlier reported values. Its simple and easy operation makes it a promising device to use as compared with other commonly employed chemical adsorption based alternate tools.

Effects of fresh and aged vehicular exhaust emissions on breathing pattern and cellular responses--pilot single vehicle study

The study presented here is a laboratory pilot study using diluted car exhaust from a single vehicle to assess differences in toxicological response between primary emissions and secondary products resulting from atmospheric photochemical reactions of gas phase compounds with O₃, OH and other radicals. Sprague Dawley rats were exposed for 5 h to either filtered room air (sham) or one of two different atmospheres: (i) diluted car exhaust (P)+Mt. Saint Helens Ash (MSHA); (ii) P+MSHA+secondary organic aerosol (SOA, formed during simulated photochemical aging of diluted exhaust). Primary and secondary gases were removed using a nonselective diffusion denuder. Continuous respiratory data was collected during the exposure, and bronchoalveolar lavage (BAL) and complete blood counts (CBC) were performed 24 h after exposure. ANOVA models were used to assess the exposure effect and to compare those effects across different exposure types. Total average exposures were 363 ± 66 μg/m³ P+MSHA and 212 ± 95 µg/m³ P+MSHA+SOA. For both exposures, we observed decreases in breathing rate, tidal and minute volumes (TV, MV) and peak and median flows (PIF, PEF and EF50) along with increases in breathing cycle times (Ti, Te) compared to sham. These results indicate that the animals are changing their breathing pattern with these test atmospheres. Exposure to P+MSHA+SOA produced significant increases in total cells, macrophages and neutrophils in the BAL and in vivo chemiluminescence of the lung. There were no significant differences in CBC parameters. Our data suggest that simulated atmospheric photochemistry, producing SOA in the P+MSHA+SOA exposures, enhanced the toxicity of vehicular emissions.

Development and evaluation of a countercurrent parallel-plate membrane diffusion denuder for the removal of gas-phase compounds from vehicular emissions

Diffusion denuders have been commonly used to remove trace gases from an aerosol (mixture of gases and particles), while allowing the particles to remain suspended in air. We present the design and evaluation of a high-flow (16.7 L min⁻¹) countercurrent parallel-plate membrane diffusion denuder that has high removal efficiencies for both non-reactive gases such as carbon monoxide (89%), as well as volatile organic compounds (80-85%) from an automobile exhaust. Particle losses were approximately 15% for particles around 100 nm in diameter. This denuder is suitable for toxicological tests involving both human and animal exposures to combustion aerosols. The denuder may also be used for other applications, for example, to reduce the effect of gas-phase sampling artifacts on particle composition.

Cardiac and pulmonary oxidative stress in rats exposed to realistic emissions of source aerosols

In vivo chemiluminescence (CL) is a measure of reactive oxygen species in tissues. CL was used to assess pulmonary and cardiac responses to inhaled aerosols derived from aged emissions of three coal-fired power plants in the USA. Sprague-Dawley rats were exposed to either filtered air or: (1) primary emissions (P); (2) ozone oxidized emissions (PO); (3) oxidized emissions + secondary organic aerosol (SOA) (POS); (4) neutralized oxidized emissions + SOA (PONS); and (5) control scenarios: oxidized emissions + SOA in the absence of primary particles (OS), oxidized emissions alone (O), and SOA alone (S). Immediately after 6 hours of exposure, CL in the lung and heart was measured. Tissues were also assayed for thiobarbituric acid reactive substances (TBARS). Exposure to P or PO aerosols led to no changes compared to filtered air in lung or heart CL at any individual plant or when all data were combined. POS caused significant increases in lung CL and TBARS at only one plant, and not in combined data from all plants; PONS resulted in increased lung CL only when data from all plants were combined. Heart CL was also significantly increased with exposure to POS only when data from all plants were combined. PONS increased heart CL significantly in one plant with TBARS accumulation, but not in combined data. Exposure to O, OS, and S had no CL effects. Univariate analyses of individual measured components of the exposure atmospheres did not identify any component associated with increased CL. These data suggest that coal-fired power plant emissions combined with other atmospheric constituents produce limited pulmonary and cardiac oxidative stress.

Laboratory evaluation of a prototype photochemical chamber designed to investigate the health effects of fresh and aged vehicular exhaust emissions

Laboratory experiments simulating atmospheric aging of motor vehicle exhaust emissions were conducted using a single vehicle and a photochemical chamber. A compact automobile was used as a source of emissions. The vehicle exhaust was diluted with ambient air to achieve carbon monoxide (CO) concentrations similar to those observed in an urban highway tunnel. With the car engine idling, it is expected that the CO concentration is a reasonable surrogate for volatile organic compounds (VOCs) emissions. Varying the amount of dilution of the exhaust gas to produce different CO concentrations, allowed adjustment of the concentrations of VOCs in the chamber to optimize production of secondary organic aerosol (SOA) needed for animal toxicological exposures. Photochemical reactions in the chamber resulted in nitric oxide (NO) depletion, nitrogen dioxide (NO₂) formation, ozone (O₃) accumulation, and SOA formation. A stable SOA concentration of approximately 40 μg m⁻³ at a chamber mean residence time of 30 min was achieved. This relatively short mean residence time provided adequate chamber flow output for both particle characterization and animal exposures. The chamber was operated as a continuous flow reactor for animal toxicological tests. SOA mass generated from the car exhaust diluted with ambient air was almost entirely in the ultrafine mode. Chamber performance was improved by using different types of seed aerosol to provide a surface for condensation of semivolatile reaction products, thus increasing the yield of SOA. Toxicological studies using Sprague-Dawley rats found significant increases of in vivo chemiluminescence in lungs following exposure to SOA.

Toxicological evaluation of realistic emission source aerosols (TERESA): summary and conclusions

The toxicological evaluation of realistic emissions of source aerosols (TERESA) study seeks to delineate health effects of aerosols formed from emissions of particulate matter sources. This series of papers reports the findings of experiments using coal-fired power plants as the source of emissions and this paper summarizes the findings and knowledge acquired from these studies. Emissions were drawn directly from the stacks of three coal-fired power plants in the US, and photochemically aged in a mobile laboratory to simulate downwind power plant plume processing. The power plants used different sources of coal and had different emission controls. Exposure scenarios included primary particles, secondary particles and mixtures of these with common atmospheric constituents (α-pinene and ammonia). Extensive exposure characterization was carried out, and toxicological outcomes were evaluated in Sprague-Dawley rats exposed to different emission scenarios. Breathing pattern, pulmonary inflammatory responses, in vivo pulmonary and cardiac chemiluminescence and cardiac response in a model of acute myocardial infarction were assessed. The results showed no response or relatively mild responses to the inhaled aerosols studied; complex scenarios which included oxidized emissions and α-pinene to simulate biogenic secondary organic aerosol tended to induce more statistically significant responses than scenarios of oxidized and non-oxidized emissions alone. Relating adverse effects to specific components did not consistently identify a toxic constituent. These findings are consistent with most of the previously published studies using pure compounds to model secondary power plant emissions, but importantly add substantial complexity and thus have considerable merit in defining toxicological responses.

Toxicological evaluation of realistic emission source aerosols (TERESA)--power plant studies: assessment of breathing pattern

Our approach to study multi-pollutant aerosols isolates a single emissions source, evaluates the toxicity of primary and secondary particles derived from this source, and simulates chemical reactions that occur in the atmosphere after emission. Three U.S. coal-fired power plants utilizing different coals and with different emission controls were evaluated. Secondary organic aerosol (SOA) derived from α-pinene and/or ammonia was added in some experiments. Male Sprague-Dawley rats were exposed for 6 h to filtered air or different atmospheric mixtures. Scenarios studied at each plant included the following: primary particles (P); secondary (oxidized) particles (PO); oxidized particles + SOA (POS); and oxidized and neutralized particles + SOA (PONS); additional control scenarios were also studied. Continuous respiratory data were obtained during exposures using whole body plethysmography chambers. Of the 12 respiratory outcomes assessed, each had statistically significant changes at some plant and with some of the 4 scenarios. The most robust outcomes were found with exposure to the PO scenario (increased respiratory frequency with decreases in inspiratory and expiratory time); and the PONS scenario (decreased peak expiratory flow and expiratory flow at 50%). PONS findings were most strongly associated with ammonium, neutralized sulfate, and elemental carbon (EC) in univariate analyses, but only with EC in multivariate analyses. Control scenario O (oxidized without primary particles) had similar changes to PO. Adjusted R(2) analyses showed that scenario was a better predictor of respiratory responses than individual components, suggesting that the complex atmospheric mixture was responsible for respiratory effects.

Electrocardiographic and respiratory responses to coal-fired power plant emissions in a rat model of acute myocardial infarction: results from the Toxicological Evaluation of Realistic Emissions of Source Aerosols Study

BACKGROUND

Ambient particulate matter (PM) derived from coal-fired power plants may have important cardiovascular effects, but existing toxicological studies are inadequate for understanding these effects. The Toxicological Evaluation of Realistic Emissions of Source Aerosols (TERESA) study aims to evaluate the toxicity of primary and secondary PM derived from coal-fired power plants. As a part of this effort, we evaluated in susceptible animals the effect of stack emissions on cardiac electrophysiology and respiratory function under exposure conditions intended to simulate an aged plume with unneutralized acidity and secondary organic aerosols (POS exposure scenario).

METHODS

Rats with acute myocardial infarction were exposed to either stack emissions (n = 15) or filtered air (n = 14) for 5 h at a single power plant. Respiration and electrocardiograms were continuously monitored via telemetry and heart rate, heart rate variability (HRV), premature ventricular beat (PVB) frequency, electrocardiographic intervals, and respiratory intervals and volumes were evaluated. Similar experiments at another power plant were attempted but were unsuccessful.

RESULTS

POS exposure (fine particle mass = 219.1 µg/m(3); total sulfate = 172.5 µg/m(3); acidic sulfate = 132.5 µg/m(3); organic carbon = 50.9 µg/m(3)) was associated with increased PVB frequency and decreased respiratory expiratory time and end-inspiratory pause, but not with changes in heart rate, HRV, or electrocardiographic intervals. RESULTS from a second power plant were uninterpretable.

CONCLUSIONS

Short-term exposure to primary and unneutralized secondary PM formed from aged emissions from a coal-fired power plant, as simulated by the POS scenario, may be associated with increased risk of ventricular arrhythmias in susceptible animals.

Toxicological evaluation of realistic emission source aerosols (TERESA): introduction and overview

Determining the health impacts of sources and components of fine particulate matter (PM(2.5)) is an important scientific goal. PM(2.5) is a complex mixture of inorganic and organic constituents that are likely to differ in their potential to cause adverse health outcomes. The Toxicological Evaluation of Realistic Emissions of Source Aerosols (TERESA) study focused on two PM sources--coal-fired power plants and mobile sources--and sought to investigate the toxicological effects of exposure to emissions from these sources. The set of papers published here document the power plant experiments. TERESA attempted to delineate health effects of primary particles, secondary (aged) particles, and mixtures of these with common atmospheric constituents. TERESA involved withdrawal of emissions from the stacks of three coal-fired power plants in the United States. The emissions were aged and atmospherically transformed in a mobile laboratory simulating downwind power plant plume processing. Toxicological evaluations were carried out in laboratory rats exposed to different emission scenarios with extensive exposure characterization. The approach employed in TERESA was ambitious and innovative. Technical challenges included the development of stack sampling technology that prevented condensation of water vapor from the power plant exhaust during sampling and transfer, while minimizing losses of primary particles; development and optimization of a photochemical chamber to provide an aged aerosol for animal exposures; development and evaluation of a denuder system to remove excess gaseous components; and development of a mobile toxicology laboratory. This paper provides an overview of the conceptual framework, design, and methods employed in the study.

Extensive evaluation of a diffusion denuder technique for the quantification of atmospheric stable and radioactive molecular iodine

In this paper we present the evaluation and optimization of a new approach for the quantification of gaseous molecular iodine (I(2)) for laboratory- and field-based studies and its novel application for the measurement of radioactive molecular iodine. alpha-Cyclodextrin (alpha-CD) in combination with (129)I(-) is shown to be an effective denuder coating for the sampling of gaseous I(2) by the formation of an inclusion complex. The entrapped (127)I(2) together with the (129)I(-) spike in the coating is then released and derivatized to 4-iodo-N,N-dimethylaniline (4-I-DMA) for gas chromatography-mass spectrometry (GC-MS) analysis. The (127)I(2) collected can be differentiated from the (129)I(-) spike by MS. A set of parameters affecting the analytical performances of this approach, including amount of alpha-CD and (129)I(-) applied, denuder length, sampling gas flow rate and sampling duration, relative humidity, sample storage period, and condition of release and derivatization of iodine, is extensively evaluated and optimized. The collection efficiency is larger than 98% and the limit of detection (LOD) obtained is 0.17 parts-per-trillion-by-volume (pptv) for a sampling duration of 30 min at 500 mL min(-1). Furthermore, the potential use of this protocol for the determination of radioactive I(2) at ultra trace level is also demonstrated when (129)I(-) used in the coating is replaced by (127)I(-) and a multiple denuder system is used. Using the present method we observed 25.7-108.6 pptv (127)I(2) at Mweenish Bay, Ireland and 10(8) molecule m(-3 129)I(2) at Mainz, Germany.

Aged particles derived from emissions of coal-fired power plants: the TERESA field results

The Toxicological Evaluation of Realistic Emissions Source Aerosols (TERESA) study was carried out at three US coal-fired power plants to investigate the potential toxicological effects of primary and photochemically aged (secondary) particles using in situ stack emissions. The exposure system designed successfully simulated chemical reactions that power plant emissions undergo in a plume during transport from the stack to receptor areas (e.g., urban areas). Test atmospheres developed for toxicological experiments included scenarios to simulate a sequence of atmospheric reactions that can occur in a plume: (1) primary emissions only; (2) H(2)SO(4) aerosol from oxidation of SO(2); (3) H(2)SO(4) aerosol neutralized by gas-phase NH(3); (4) neutralized H(2)SO(4) with secondary organic aerosol (SOA) formed by the reaction of α-pinene with O(3); and (5) three control scenarios excluding primary particles. The aged particle mass concentrations varied significantly from 43.8 to 257.1 µg/m(3) with respect to scenario and power plant. The highest was found when oxidized aerosols were neutralized by gas-phase NH(3) with added SOA. The mass concentration depended primarily on the ratio of SO(2) to NO(x) (particularly NO) emissions, which was determined mainly by coal composition and emissions controls. Particulate sulfate (H(2)SO(4) + neutralized sulfate) and organic carbon (OC) were major components of the aged particles with added SOA, whereas trace elements were present at very low concentrations. Physical and chemical properties of aged particles appear to be influenced by coal type, emissions controls and the particular atmospheric scenarios employed.

Development of an Exposure System for the Toxicological Evaluation of Particles Derived from Coal-Fired Power Plants

To investigate the toxicity of particles originating from coal-fired power plants it is necessary to consider the effects of both primary particles and secondary components formed in the air through atmospheric reactions. This report describes a new exposure system that can be used to expose animals to both directly emitted particles and to secondary particles. The system consists of three main components. The first is a sampling system to continuously collect and dilute power plant stack emissions. The second is a reaction laboratory that contains reaction chambers to simulate atmospheric reactions. The following atmospheric reactions were simulated: (1) the oxidation of sulfur dioxide to form sulfuric acid, (2) the neutralization of sulfuric acid by ammonia, and (3) the reaction of alpha-pinene with ozone to form secondary organic aerosol. Using these chambers with the diluted emissions, different typical atmospheric scenarios can be simulated. The final component is a mobile toxicology laboratory where animals are exposed to the resulting test aerosols. We report here the characteristics of the test aerosol exposures obtained at a coal-fired electric power plant. Particle exposures were characterized for concentrations of mass, elements, elemental carbon, organic species, inorganic ions, strong acidity, particle number, and size distributions. Mass concentrations ranged from a few micrograms per cubic meter for a scenario of primary emissions only, to about 250 microg m(-3) for the most complex scenario. We show that the different scenarios produced a large variation in the composition of the test aerosol, thus potentially changing the toxicity of the emissions.