Evaluation of the Effects of Ozone Oxidation on Redox-Cycling

Kwamena , N.-O. A.; Earp , M. E.; Young , C. J.; Abbatt , J. P. D. Kinetic and ..... Li , Q.; Wyatt , A.; Kamens , R. M. Oxidant generation and toxici...
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Evaluation of the Effects of Ozone Oxidation on Redox-Cycling Activity of Two-Stroke Engine Exhaust Particles Robert D. McWhinney,* Shawna S. Gao, Shouming Zhou, and Jonathan P. D. Abbatt Department of Chemistry, University of Toronto, Toronto ON Canada

bS Supporting Information ABSTRACT: The effect of oxidation on the redox-cycling activity of engine exhaust particles is examined. Particles obtained from a two-stroke gasoline engine were oxidized in a flow tube with ozone on a one-minute time scale both in the presence and absence of substantial gas-phase exhaust components. Whereas ozone concentrations were high, the ozone exposures were approximately equivalent to 60 ppb ozone for 2-8 h. Oxidation led to substantial increases in redox-cycling of aqueous extracts of filtered particles, as measured using the dithiothreitol (DTT) assay. Increases in redox activity when the entire exhaust was oxidized were primarily driven by deposition of redox-active secondary organic aerosol (SOA), resulting in an upper-limit DTT activity of 8.6 ( 2.0 pmol DTT consumed per min per microgram of particles, compared to 0.73 ( 0.60 pmol min-1 μg-1 for fresh, unoxidized exhaust particles. Redox-cycling activity reached higher levels when VOC denuded exhaust was oxidized, with the highest DTT activity observed being 16.7 ( 1.6 pmol min-1 μg-1 with no upper limit reached for the range of ozone exposures used in this study. Our results provide laboratory support for the hypothesis that the toxicity of engine combustion particles due to redox-cycling may increase as they age in the atmosphere.

’ INTRODUCTION Airborne particulate matter (PM) pollution is of concern for a myriad of reasons, among which is its demonstrated ability to adversely affect human health. A number of epidemiological studies have observed negative effects on both respiratory and cardiovascular health as a result of both acute 1,2 and chronic 3,4 exposure to PM pollution. Evidence is mounting that oxidative stress-an imbalance of oxidants and antioxidants in biological systems-is an important toxicological mechanism resulting from PM inhalation.5,6 A number of chemical mechanisms involving specific PM components may induce oxidative stress. Redox-cycling reactions are one such mechanism, in which the presence of a suitable catalyst results in depletion of reducing agents within the cell and the generation of reactive oxygen species; catalysts with multiple and labile oxidation states, including transition metals 7 and quinones,8 are known to partake in such reactions. In a general redox cycle, cellular reducing agents such as glutathione and ascorbate are consumed by reduction of the catalyst, which is reoxidized by reducing oxygen to superoxide and hydrogen peroxide, allowing the cycle to repeat.7,8 To assess the capacity of particulate matter to catalyze redox-cycling in solution, the dithiothreitol assay has been developed by Kumagai et al.9 Dithiothreitol (DTT) acts as the reducing agent in place of biological reductants such as glutathione, which, like DTT, contains thiol groups as the active reducing chemical moiety (Scheme S1 in the Supporting Information outlines the mechanism of DTT consumption). The decay rate of DTT in aqueous PM extracts has been correlated with the expression of the r 2011 American Chemical Society

oxidative stress marker heme oxygenase-1 in cellular systems.10 Although it is an indirect measure of one aspect of toxicity, the assay provides a simple, acellular, and biologically relevant technique for measuring the potential toxicity of particulate matter arising from redox-cycling activity. While they are certainly not the only potential redox-cycling agents, quinones are often considered to be one species involved in such chemistry. They are common constituents of the atmosphere 11-16 and of both gasoline and diesel combustion particles.11,17 In addition, they are oxidation products of polycyclic aromatic hydrocarbons (PAHs) through both gas-phase 18-20 and heterogeneous oxidation.21,22 Recent studies have shown that PAH chemical lifetimes in the atmosphere can be shorter than particle deposition lifetimes.23,24 This suggests that the redox-cycling activity of PAH-containing particles may increase with atmospheric processing. Among a number of field measurements applying the DTT assay to ambient particles,25-29 there are findings to support this hypothesis; quasi-ultrafine particles measured in Los Angeles displayed higher redox activity in the afternoon compared to the morning, as well as higher water-soluble organic carbon and lower PAH and hydrocarbon loadings, indicative of higher SOA mass.29 Particle loadings of 9,10-phenanthrenequinone have been observed to increase as air masses age in the Los Angeles basin,30 indicating that photochemical production of Received: August 20, 2010 Accepted: February 1, 2011 Revised: January 18, 2011 Published: February 22, 2011 2131

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Environmental Science & Technology quinones is observable in the field. Therefore, it is important to understand what effect the aging process may have on redoxcycling activity, and thus toxicity, of organic particles. One study, using a large outdoor chamber to age diesel exhaust particles in the dark with ozone, noted that redox-cycling activity for aged particles was more than twice that of particles aged without ozone.31 While important, this experiment was limited to one ozone concentration, so little can be inferred about mechanistic aspects behind the redox-cycling increase. To our knowledge, there are no controlled oxidation experiments studying the incremental effects of particle oxidation on redox-cycling activity, or the oxidation mechanisms that lead to enhanced redox activity, such as whether the chemistry occurs in the gas phase or heterogeneously. In this study, we pose the question: Is there a quantifiable effect on redox-cycling activity upon exposure of combustion particles containing PAHs to different oxidant concentrations? We have used ozone as an oxidizing species to process combustion particles from a two-stroke gasoline engine in controlled flow-tube experiments. Two-stroke engines emit much higher mass concentrations of particles and volatile organic compounds (VOCs) than four-stroke gasoline engines. Although contributions of two-stroke engines to PM budgets are not well constrained, small hand-held spark ignition engines, comprised of mostly two-stroke engines, were estimated to account for 6% of mobile source VOCs and 4% of mobile source particles in the United States in 2002, and are expected to contribute to 8% of mobile source PM by 2030 in the absence of further regulation.32 In Asia, it has been reported that two-stroke engines are even more prominent, with powered two-wheeled vehicles accounting for 75% of vehicles, approximately 85% of which use two-stroke engines.33 The particles themselves are poorly studied, compared to four-stroke gasoline exhaust particles or diesel exhaust particles, and represent a unique combustion source for study. Unlike gasoline or diesel exhaust particles, two-stroke engine particles are large particles composed primarily of residual fuel oil.34 To gather insight into the mechanism underlying the changes in redox-cycling activity, we have carried out experiments under a range of oxidant concentrations and under two major exhaust conditions. In the whole-exhaust experiments, we have exposed the unaltered gas- and particle-phase components of the exhaust to ozone to represent the oxidation of fresh, undiluted exhaust. In the denuded-exhaust experiments, we have passed the exhaust through a VOC denuder prior to oxidation to alter the partitioning behavior of semivolatile species in the aerosol, better representing oxidation conditions following dilution of the exhaust.

’ EXPERIMENTAL SECTION Particle Oxidation. A two-stroke Homelite trimmer gasoline engine was used as a source of combustion particles for these experiments. The fuel was a mixture of 20 mL of synthetic twocycle oil per 1 L of regular gasoline. The experimental setup is illustrated in Figure S1 of the Supporting Information. The engine was run for 3-5 min and a portion of the exhaust was directed by a blower into a 0.5 m3 fluorinated ethylene propylene (FEP) bag. The contents of the bag were pulled through two vertically mounted glass flow tubes (80 cm  4 cm i.d.) at a volumetric flow rate of 900 ccm (cm3 min-1). An additional 100 ccm of oxygen in nitrogen were added to both the control and oxidation flow tubes to bring the total flow to 1000 ccm. For the

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oxidation flow tube, the mixture of oxygen in nitrogen was passed over a UVP mercury pen-ray lamp (λ = 185 nm) to generate ozone. Ozone concentration was controlled by altering the ratio of oxygen to nitrogen and was measured by absorption of the 254 nm light from a second pen-ray lamp. The average residence time of the particles in the flow tube was 1 min. Following oxidation, the particles from the oxidation flow tube were passed through a diffusion ozone denuder filled with CARULITE 200 manganese dioxide/copper oxide catalyst (Carus Corporation, Peru IL USA, 96% efficiency at 1000 ccm flow). Control and oxidized particles were collected on separate Zefluor polytetrafluoroethylene (PTFE) membrane filters (Pall Life Sciences, 2 μm pore size, 47 mm diameter, catalogue no. P5PJ047). To minimize the potential effect of oxidation of filtered particles by bleed-through of ozone from the denuder, the sampling period was limited to 40 min. To probe the difference between the oxidation of the whole exhaust (i.e., gas- and particle-phase oxidation) and the oxidation of the particles with lower VOC concentrations, additional experiments were performed using exhaust pulled through an activated carbon (Sigma-Aldrich, 4-14 mesh, catalogue no. 292591) volatile organic compound (VOC) denuder before entering the flow tubes. The efficiency of VOC removal was measured using a Proton Transfer Reaction Mass Spectrometer (PTR-MS, Ionicon, Innsbruck Austria) to measure relative intensities of select gas-phase species before and after the VOC denuder. To examine the effects of oxidation on the particle chemistry, the particles were characterized with a time-of-flight aerosol mass spectrometer (ToF-AMS, Aerodyne Research, Billerica MA USA; see Drewnick et al.35 for further details on the intrument). Briefly, the AMS measures the mass spectrum of nonrefractory components of aerosols by focusing particles into a beam using an aerodynamic lens and flash vaporizing the particles in a tungsten furnace. The vapors are ionized by electron impact and ions are separated with unit mass resolution in a time-of-flight mass spectrometer. The instrument was operated in both mass spectrum (MS) mode, where the total mass spectrum was measured, and particle time-of-flight (PToF) mode, where size-resolved mass spectra were obtained. The AMS data were collected from the control and oxidized particles by means of a three-way valve switched every two minutes. When the three-way valve is opened, a small portion of the particles is sampled and diluted with nitrogen so as to avoid saturation of the AMS detector. Particle Characterization. Additional characterization was carried out for fresh exhaust particles. Particle-bound PAHs were measured by gas chromatography-mass spectrometry (GSMS). Elemental and organic carbon (EC and OC, respectively) analyses were performed by Natural Resources Canada, CANMET Mining and Minerals Sciences Laboratories (Sudbury ON Canada). Size distributions were obtained using a scanning mobility particle sizer (SMPS; TSI, Shoreview MN USA). Further experimental details may be found in the Supporting Information. DTT Assay. The procedure used in these experiments has been adapted from that described by Cho et al.25 Details of the procedure are included in the Supporting Information. Both the absolute DTT consumption rates in M min-1 for the whole filter extract and the DTT consumption rates normalized to the mass of particles collected on the filter, mfilter, in pmol min-1 μg-1 will be discussed. For clarity, the absolute DTT consumption rate 2132

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Environmental Science & Technology (-d[DTT]/dt) is defined as Z and the mass normalized DTT consumption rate (-(dnDTT/dt)/mfilter) is defined as ζ.

’ RESULTS AND DISCUSSION Engine Characterization. Particles from a two-stroke engine differ in nature from typical gasoline and diesel exhaust particles. The particles are of the accumulation mode size range and the size distribution depends on the speed and load of the engine and the fuel-oil ratio, whereas the particle type is dominated by lubricating oil droplets rather than incomplete combustion products.34 The chemistry of the particles is reflected in the very low mass ratio of elemental to organic carbon, which was measured as (8 ( 2)  10-2. Characteristics of the engine exhaust may be found in the Supporting Information, including particle size, gas-phase components measured by the PTR-MS, AMS particle mass spectra, and PAH content. Whole-Exhaust Oxidation. The DTT consumption rate of aqueous particle extracts consistently increased upon oxidation of the whole exhaust compared to the control particles. The redox-cycling activity of unoxidized particles was quite low, with an average Z of (2.5 ( 2.4)  10-8 M min-1. Z for the oxidized whole-exhaust particle extracts ranged up to 22 times greater than the average control consumption rate. Average particle loadings in the flow tube were high, ranging from 7000-33 000 μg m-3. The value of Z for the whole-exhaust filter extracts was linearly dependent on the ozone exposure in the flow tube (Figure 1). Even though the particle mass loading within the FEP chamber was not controlled, Z was independent of the mass of filtered particles. A linear best-fit yielded an r2 of 0.97 and a slope of (4.54 ( 0.17)  10-20 (M min-1)/(molecules cm-3 hr) (Table 1 for a summary of the parameters derived in this study).

Figure 1. Absolute DTT consumption rate (Z) for whole-exhaust (filled circles) and denuded-exhaust (open triangles) oxidation experiments as a function of ozone exposure. The linear best-fit is displayed for the whole-exhaust data. Error bars denote the nonlinear propagation of standard deviations from DTT decay fits and duplicate averaging.

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This response is explained if the ozone is the limiting reagent and the oxidation generated a constant amount of redox-active organic species per unit of ozone reacted. There was evidence of a significant amount of secondary organic aerosol (SOA) generated in the ozone flow tube, with a white deposit gradually generated on its inner walls and a substantial increase in filtered particle mass upon oxidation. Averaging the AMS PToF size distribution over all experiments, fresh particles had a geometric mean vacuum aerodynamic diameter (Dva) of 279 nm, whereas oxidized particles had a geometric mean diameter of 361 nm. Dva depends not only on the physical diameter of the particle but also the particle shape and density. Measurements of mobility diameter, Dm, verify particle growth due to SOA formation (Supporting Information for measurements). The increase in Dm, on the order of 10-30 nm, representing a 10 ( 8% increase in volume, is smaller than the increase in Dva, indicating that a substantial increase in density accompanies SOA formation. Should the redox-active species be coming from condensation of gas-phase oxidation products, the mass-normalized DTT activity will approach an upper limit corresponding to the ζ of the pure SOA. For each filter extract, the overall ζfilter will be a mass-weighted average of the redox activities for the fresh particle core and the added SOA mass: ζf ilter ¼

mf resh ζf resh þ ½O3 tySOA ζSOA mf resh þ ½O3 tySOA

ð1Þ

This relationship assumes a constant ySOA, defined as the mass yield of SOA in micrograms per unit ozone exposure. Equation 1 also assumes a constant mass for the fresh particle core, and, while this is not strictly true, the effect should be negligible due to the low value of ζfresh. A plot of ζfilter versus ozone exposure (Figure 2) indeed shows evidence of an upper limit. Fitting to 1 yields a ζfresh of 0.71 ( 0.26 pmol min-1 μg-1, in excellent agreement with the average of control filters (0.73 ( 0.60 pmol min-1 μg-1),

Figure 2. Mass-normalized DTT consumption rate (ζfilter) for whole exhaust as a function of ozone exposure. The black line is the fit of the data to eq 1.

Table 1. Major Parameters Derived from This Study parameter

value -20

(4.54 ( 0.17)  10

dZ/d([O3]t) for whole exhaust

0.73 ( 0.60 pmol min

ζfresh, calculated

(M min-1)/(molecules cm-3 hr)

-1

μg-1

-1

ζfresh, from fit ζSOA, from fit (ozone data)

0.71 ( 0.26 pmol min μg-1 8.6 ( 2.0 pmol min-1 μg-1

Δζ per 0.01 increase in f44 for denuded-exhaust oxidation

8.8 ( 1.6 pmol min-1 μg-1 2133

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Figure 3. Mass-normalized DTT consumption rate (ζ) for denudedexhaust oxidation as a function of the product of ozone exposure and surface area-to-mass ratio.

and a ζSOA of 8.6 ( 2.0 pmol min-1 μg-1. Fitted values for mfresh and ySOA had very large errors and are not reported. We believe the SOA formation is occurring via ozone interactions with unsaturated components of the engine exhaust, such as alkenes. Denuded Exhaust Oxidation. To examine how the redoxcycling activity response changes under conditions more representative of diluted particles, a set of experiments was conducted using an activated carbon denuder to remove VOCs from the exhaust before oxidation in the flow tube. Whereas particle and oxidant concentrations remain high, the removal of VOCs reduces the amount of SOA formation and allows for the repartitioning of semivolatile species as would occur upon dilution. The denuder was efficient in removing VOCs from the engine exhaust as measured by the PTR-MS. In particular, the total signal measured between a mass-to-charge (m/z) ratio of 22 and 150 decreased by 97%. The naphthalene signal at m/z 129, corresponding to [C10H8-H]þ, decreased by 96%, and most of the lightweight alkenes and aromatic compounds that made up the bulk of the signal decreased in intensity by 98-99% (Supporting Information for PTR-MS spectra of the VOCs before and after the denuder). In contrast with the results from whole-exhaust oxidation, Z for the denuded-exhaust oxidation was no longer linearly dependent on ozone exposure, as is seen in Figure 1, suggesting that between-run differences in particle loading, surface area, or composition are now important. Average PToF size distributions showed the geometric mean Dva increased to 324 nm for oxidized particles from 279 nm for fresh particles. Size measurements do not show a physical diameter increase more than the approximately 15 nm resolution of the SMPS, indicating that much of the increase in Dva is a result of an increase in particle density and confirming the decreased role of SOA formation. Average particle loadings in the flow tube for denuded-exhaust experiments ranged from 2000-15 000 μg m-3. If heterogeneous oxidation is playing a role in the increase in redox-active species, there will be a surface area dependence in the DTT activity. To examine this, the surface area-to-mass ratio was calculated from the AMS PToF size distribution (Supporting Information for related calculations). Whereas the scatter from plotting ζ as a function of the product of ozone exposure and the surface area-to-mass ratio (Figure 3) is indeed lower than that for the denuded-exhaust data in Figure 1 (the r2 for a linear best-fit increases from 0.30 to 0.52), the data still do not show a tight correlation. The increase in linearity suggests that a heterogeneous oxidation mechanism is leading to some of the observed

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Figure 4. Mass-normalized DTT consumption rate (ζ) as a function of AMS measured f44 for whole-exhaust oxidation (closed circles) and denuded-exhaust oxidation (open triangles). The dashed line is a linear best-fit of the denuded-exhaust oxidation data. Data from the experiments using three VOC denuders (diamonds) is included for comparison, although the error bars are omitted for clarity due to large uncertainties.

increase in redox-cycling activity. Remaining scatter may be a result of residual gas-phase chemistry resulting from VOC offgassing to reestablish equilibrium after the denuder, or due to differences in surface reactivity between runs if heterogeneous oxidation is occurring. To test the VOC off-gassing hypothesis, one set of experiments was carried out with three VOC denuders in series to remove as many of the volatile constituents as possible. The response to oxidation, shown in Figure 4, remains similar to the other denuded-exhaust oxidation experiments, although with very high uncertainty due to low mass on the filters from particle loss in the denuders and thus low signal. The residence time of the particles in the denuders has only increased to about 30 s, which is still shorter than the residence within the flow tube. Therefore, we cannot conclusively determine if the observed increase in redox-cycling is due to heterogeneous oxidation or SOA formation under the VOC denuded conditions. However, particle size measurements confirm that, under denuded conditions, SOA formation is reduced, if not eliminated. Particle Chemistry and Redox-Cycling Activity. Characterization of particle chemistry with the AMS allowed for the comparison of redox-cycling activity with the final oxidation state of the particle. Degree of oxidation of organic aerosol is often represented using f44, the ratio of the organic mass at m/z 44 (CO2þ) to the total organic mass, as the CO2þ fragment is known to be produced from oxidized organics, particularly organic acids.36 It is evident from Figure 4 that the whole-exhaust experiments lead to much higher degrees of oxidation but lower redox-cycling activity per mass of particle than do denuded-exhaust experiments. They also approach an asymptotic value corresponding to ζSOA. Conversely, the denuded-exhaust oxidation data reveals relatively low oxidation of the organic particles but much higher redox-cycling activity per unit mass of particles collected compared to the whole-exhaust oxidation. Under the oxidation conditions of this study, the increase in redox-cycling activity for VOC denuded exhaust is linearly dependent on f44 (with a much higher degree of correlation, r2 = 0.71). As such, the redoxcycling activity is expected to increase upon further oxidation beyond what has been measured under these conditions. The scatter observed in Figure 3 is much reduced when plotting against f44 as in Figure 4. Regardless of whether a gas-phase or 2134

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Environmental Science & Technology heterogeneous oxidation mechanism is driving the response in the denuded-exhaust data in Figure 4, it is noteworthy that the proportion of redox-active products remains consistent with the degree of oxidation, indicating that the mechanism is also consistent despite run-to-run changes in conditions. We anticipate that with an even higher level of oxidation the response will saturate due to depletion of reactive precursors. To our knowledge, this is the first demonstration that increasing levels of oxidation of engine exhaust has been correlated to increased redox-cycling activity. Atmospheric Implications. Ozone exposures used are in a range similar to ambient conditions, being approximately equivalent to ozone exposure during 2-8 h at 60 ppb of ozone. However, we stress that, due to high particle loadings and short reaction times, the applicability of the results to ambient conditions is potentially limited. Particle loadings are orders of magnitude higher than typical ambient conditions, and as such partitioning of semivolatile species will be biased toward the particle phase compared to ambient conditions. Additionally, while working at elevated oxidant concentrations increases the rate of oxidation, the rates of other processes such as gas-particle partitioning and in-particle reactions do not similarly increase and thus their roles are de-emphasized. Depending on the importance of processes secondary to the oxidation, observations under flow tube conditions may differ substantially from what may result from actual atmospheric aging. For future work, we intend to extend this initial study to conditions more representative of atmospheric concentrations. In addition, while it is not an insignificant particle source, two-stroke exhaust is not fully representative of all ambient particles, which will also include motor vehicle exhaust, noncombustion related secondary organic constituents, and inorganic constituents. Nonetheless, it is worthwhile to discuss our results as they relate to previous measurements of redox-cycling activity. The engine particles measured are primarily larger accumulation mode particles. DTT activity of accumulation mode particles has been measured to be 14-24 pmol min-1 μg-1 in Los Angeles and Long Beach, California,26 approximately 40 pmol min-1 μg-1 in Mexico City,27 and 21-75 pmol min-1 μg-1 in Downey and Riverside, California, and tunnel and roadside sites near Los Angeles.28 The activity of engine SOA from this study is below the lowest of these measurements. The highest DTT consumption rate of 16.7 ( 1.6 pmol min-1 μg-1 is measured for the denuded-exhaust oxidation experiments. If the observed ambient redox-cycling activities result from oxidation of primary organic particles, it seems more plausible that the processes observed in the denuded-exhaust experiments lead to the ambient levels of redox-cycling activity, given the lower activity of the whole-exhaust SOA. However, compared to the activity of unprocessed gasoline and diesel particles -12 pmol min-1 μg-1 and 18-25 pmol min-1 μg-1 respectively37- the DTT consumption rate for two-stroke particles is quite low. Li et al. have performed dark ozone oxidation on diesel exhaust particles using an outdoor smog chamber with a maximum ozone concentration of 320 ppb; redox-cycling activity of the particles increased by approximately an order of magnitude in the first hour of oxidation.31 The chamber experiment is difficult to directly compare to our results, but the ozone exposures and relative increases in redox-cycling activity of the engine particles are of similar magnitude. The units were normalized to a standard and are thus not directly comparable to other redoxcycling measurements reported here, but if the reported DTT

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consumption rate of approximately 20 pmol min-1 μg-1 for diesel exhaust particles 37 is applicable, the redox activity of the oxidized particles in Li et al.31 approaches approximately 200 pmol min-1 μg-1, well above those measured for ambient particles. While it is unambiguous that redox-cycling activity increases dramatically with oxidation for two-stroke engine particles, the specific quantitative values obtained in this study will not be directly applicable to ambient particles, which are influenced by motor vehicle exhaust, secondary organic, and inorganic constituents. However, our experiments are the first to indicate a clear relationship between the degree of potential toxicity arising from redox-cycling and the level of organic particle oxidative processing. Future experiments that attribute this increase in DTT activity to specific chemical species are now needed.

’ ASSOCIATED CONTENT

bS

Supporting Information. Details on exhaust characteristics and composition, a generalized DTT redox-cycling scheme, the DTT assay procedure used, additional calculations, and a schematic of the experimental setup are available. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT The authors would like to acknowledge CFCAS and NSERC CGS-D for providing funding for this project. Thanks to Ying Lei for her assistance in the PAH analysis. ’ REFERENCES (1) Dockery, D. W.; Pope, C. A. Acute respiratory effects of particulate air pollution. Annu. Rev. Public Health 1994, 15, 107–132. (2) Anderson, R. W.; Anderson, H. R.; Sunyer, J.; Ayres, J. G.; Baccini, M.; Vonk, J. M.; Boumghar, A.; Forastiere, F.; Forsberg, B.; Touloumi, G.; Schwartz, J.; Katsouyanni, K. Acute effects of particulate air pollution on respiratory admissions: Results from APHEA 2 project. Am. J. Respir. Crit. Care Med. 2001, 164, 1860–1866. (3) Pope, C. A.; Burnett, R. T.; Thun, M. J.; Calle, E. E.; Krewski, D.; Ito, K.; Thurston, G. D. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. JAMA, J. Am. Med. Assoc. 2002, 287, 1132–1141. (4) Pope, C. A.; Burnett, R. T.; Thurston, G. D.; Thun, M. J.; Calle, E. E.; Krewski, D.; Godleski, J. J. Cardiovascular mortality and long-term exposure to particulate air pollution: epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004, 109, 71–77. (5) Gurgueira, S. A.; Lawrence, J.; Coull, B.; Murthy, G. G. K.; Gonzalez-Flecha, B. Rapid increases in the steady-state concentration of reactive oxygen species in the lungs and heart after particulate air pollution inhalation. Environ. Health Perspect. 2002, 110, 749–755. (6) Gonzalez-Flecha, B. Oxidant mechanisms in response to ambient air particles. Mol. Aspects Med. 2004, 25, 169–182. (7) Netto, L. E. S.; Stadtman, E. R. The iron-catalyzed oxidation of dithiothreitol is a biphasic process: hydrogen peroxide is involved in the initiation of a free radical chain of reactions. Arch. Biochem. Biophys. 1996, 333, 233–242. (8) Squadrito, G. L.; Cueto, R.; Dellinger, B.; Pryor, W. A. Quinoid redox cycling as a mechanism for sustained free radical generation by inhaled airborne particulate matter. Free Radical Biol. Med. 2001, 31, 1132–1138. 2135

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Environmental Science & Technology (9) Kumagai, Y.; Koide, S.; Taguchi, K.; Endo, A.; Nakai, Y.; Yoshikawa, T.; Shimojo, N. Oxidation of proximal protein sulfhydryls by phenanthraquinone, a component of diesel exhaust particles. Chem. Res. Toxicol. 2002, 15, 483–489. (10) Li, N.; Sioutas, C.; Cho, A.; Schmitz, D.; Misra, C.; Sempf, J.; Wang, M.; Oberley, T.; Froines, J.; Nel, A. Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environ. Health Perspect. 2003, 111, 455–460. (11) Cho, A. K.; Stefano, E. D.; You, Y.; Rodriguez, C. E.; Schmitz, D. A.; Kumagai, Y.; Miguel, A. H.; Eiguren-Fernandez, A.; Kobayashi, T.; Avol, E.; Froines, J. R. Determination of four quinones in diesel exhaust particles, SRM 1649a, and atmospheric PM2:5. Aerosol Sci. Technol. 2004, 38, 68–81. (12) Chung, M. Y.; Lazaro, R. A.; Lim, D.; Jackson, J.; Lyon, J.; Rendulic, D.; Hasson, A. S. Aerosol-borne quinones and reactive oxygen species generation by particulate matter extracts. Environ. Sci. Technol. 2006, 40, 4880–4886. (13) Valavanidis, A.; Fiotakis, K.; Vlahogianni, T.; Papadimitriou, V.; Pantikaki, V. Determination of selective quinones and quinoid radicals in airborne particulate matter and vehicular exhaust particles. Environ. Chem. 2006, 3, 118–123. (14) Tsapakis, M.; Stephanou, E. G. Diurnal cycle of PAHs, nitroPAHs, and oxy-PAHs in a high oxidation capacity marine background atmosphere. Environ. Sci. Technol. 2007, 41, 8011–8017. (15) Eiguren-Fernandez, A.; Miguel, A. H.; Stefano, E. D.; Schmitz, D. A.; Cho, A. K.; Thurairatnam, S.; Avol, E. L.; Froines, J. R. Atmospheric distribution of gas- and particle-phase quinones in Southern California. Aerosol Sci. Technol. 2008, 42, 854–861. (16) Ahmed, S.; Kishikawa, N.; Ohyama, K.; Maki, T.; Kurosaki, H.; Nakashima, K.; Kuroda, N. An ultrasensitive and highly selective determination method for quinones by high-performance liquid chromatography with photochemically initiated luminol chemiluminescence. J. Chromatogr., A 2009, 1216, 3977–3984. (17) Jakober, C. A.; Riddle, S. G.; Robert, M. A.; Destaillats, H.; Charles, M. J.; Green, P. G.; Kleeman, M. J. Quinone emissions from gasoline and diesel motor vehicles. Environ. Sci. Technol. 2007, 41, 4548–4554. (18) Sasaki, J.; Aschmann, S. M.; Kwok, E. S. C.; Atkinson, R.; Arey, J. Products of the gasphase OH and NO3 radical-initiated reactions of naphthalene. Environ. Sci. Technol. 1997, 31, 3173–3179. (19) Wang, L.; Atkinson, R.; Arey, J. Formation of 9,10-phenanthrenequinone by atmospheric gas-phase reactions of phenanthrene. Atmos. Environ. 2007, 41, 2025–2035. (20) Kautzman, K. E.; Surratt, J. D.; Chan, M. N.; Chan, A. W. H.; Hersey, S. P.; Chhabra, P. S.; Dalleska, N. F.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H. Chemical composition of gasand aerosol-phase products from the photooxidation of naphthalene. J. Phys. Chem. A 2010, 114, 913–934. (21) Mmereki, B. T.; Donaldson, D. J.; Gilman, J.; Eliason, T. L.; Vaida, V. Kinetics and products of the reaction of gas-phase ozone with anthracene adsorbed at the air-aqueous interface. Atmos. Environ. 2004, 38, 6091–6103. (22) Kwamena, N.-O. A.; Earp, M. E.; Young, C. J.; Abbatt, J. P. D. Kinetic and product yield study of the heterogeneous gas-surface reaction of anthracene and ozone. J. Phys. Chem. A 2006, 110, 3638–3646. (23) Poschl, U.; Letzel, T.; Schauer, C.; Niessner, R. Interaction of ozone and water vapor with spark discharge soot aerosol particles coated with benzo[a]pyrene: O3 and H2O adsorption,benzo[a]pyrene degradation, and atmospheric implications. J. Phys. Chem. A 2001, 105, 4029–4041. (24) Kwamena, N.-O. A.; Staikova, M. G.; Donaldson, D. J.; George, I. J.; Abbatt, J. P. D. Role of the aerosol substrate in the heterogeneous ozonation reactions of surface-bound PAHs. J. Phys. Chem. A 2007, 111, 11050–11058. (25) Cho, A. K.; Sioutas, C.; Miguel, A. H.; Kumagai, Y.; Schmitz, D. A.; Singh, M.; Eiguren-Fernandez, A.; Froines, J. R. Redox activity of airborne particulate matter at different sites in the Los Angeles Basin. Environ. Res. 2005, 99, 40–47.

ARTICLE

(26) Hu, S.; Polidori, A.; Arhami, M.; Shafer, M. M.; Schauer, J. J.; Cho, A.; Sioutas, C. Redox activity and chemical speciation of size fractioned PM in the communities of the Los Angeles-Long Beach harbor. Atmos. Chem. Phys. 2008, 8, 6439–6451. (27) Mugica, V.; Ortiz, E.; Molina, L.; Vizcaya-Ruiz, A. D.; Nebot, A.; Quintana, R.; Aguilar, J.; Alcantara, E. PM composition and source reconciliation in Mexico City. Atmos. Environ. 2009, 43, 5068–5074. (28) Ntziachristos, L.; Froines, J. R.; Cho, A. K.; Sioutas, C. Relationship between redox activity and chemical speciation of size-fractionated particulate matter. Part. Fibre Toxicol. 2007, 4, 5. (29) Verma, V.; Ning, Z.; Cho, A. K.; Schauer, J. J.; Shafer, M. M.; Sioutas, C. Redox activity of urban quasi-ultrafine particles from primary and secondary sources. Atmos. Environ. 2009, 43, 6360–6368. (30) Eiguren-Fernandez, A.; Miguel, A. H.; Lu, R.; Purvis, K.; Grant, B.; Mayo, P.; Stefano, E. D.; Cho, A. K.; Froines, J. Atmospheric formation of 9,10-phenanthraquinone in the Los Angeles air basin. Atmos. Environ. 2008, 42, 2312–2319. (31) Li, Q.; Wyatt, A.; Kamens, R. M. Oxidant generation and toxicity enhancement of aged-diesel exhaust. Atmos. Environ. 2009, 43, 1037–1042. (32) Control of Emissions from Marine SI and Small SI Engines, Vessels, and Equipment; Final Regulatory Impact Analysis; United Stated Environmental Protection Agency: Washington, DC, 2008; http://www. epa.gov/otaq/regs/nonroad/marinesi-equipld/420r08014.pdf. (33) Adam, T.; Farfaletti, A.; Montero, L.; Martini, G.; Manfredi, U.; Larsen, B.; Santi, G. D.; Krasenbrink, A.; Astorga, C. Chemical characterization of emissions from modern two-stroke mopeds complying with legislative regulation in Europe (EURO-2). Environ. Sci. Technol. 2010, 44, 505–512. (34) Patschull, J.; Roth, P. Measurement and reduction of particles emitted from a two-stroke engine. J. Aerosol Sci. 1995, 26, 979–987. (35) Drewnick, F.; Hings, S. S.; DeCarlo, P.; Jayne, J. T.; Gonin, M.; Fuhrer, K.; Weimer, S.; Jimenez, J. L.; Demerjian, K. L.; Borrmann, S.; Worsnop, D. R. A new time-of-flight aerosol mass spectrometer (TOFAMS) - Instrument description and first field deployment. Aerosol Sci. Technol. 2005, 39, 637–658. (36) Aiken, A. C.; et al. O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-offlight aerosol mass spectrometry. Environ. Sci. Technol. 2008, 42, 4478–4485. (37) Cheung, K. L.; Ntziachristos, L.; Tzamkiozis, T.; Schauer, J. J.; Samaras, Z.; Moore, K. F.; Sioutas, C. Emissions of particulate trace elements, metals and organic species from gasoline, diesel, and biodiesel passenger vehicles and their relation to oxidative potential. Aerosol Sci. Technol. 2010, 44, 500–513.

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