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Epidemiologic studies have shown associations between ambient particulate matter (PM) and adverse health outcomes including increased mortality, emergency room visits, and time lost from school and work. The mechanisms of PM-related health effects are still incompletely understood, but a hypothesis under investigation is that many of the adverse health effects may derive from oxidative stress, initiated by the formation of reactive oxygen species (ROS) within affected cells. While the adverse effects from PM have historically been associated with the airborne concentration of PM and more recently fine-particle PM, we considered it relevant to develop an assay to quantitatively measure the ability of PM to catalyze ROS generation as the initial step in the induction of oxidative stress. This ability of PM could then be related to different sources, chemical composition, and physical and spatial/temporal characteristics in the ambient environment. The measurement of ROS-forming ability in relation to sources and other factors will have potential relevance to control of redox-active PM. If oxidative stress represents a relevant mechanism of toxicity from PM, the measurement of redox activity represents a first step in the elucidation of the subsequent downstream processes. We have developed an assay for PM redox activity, utilizing the reduction of oxygen by dithiothreitol which serves as an electron source. We have found that PM will catalyze the reduction of oxygen and have examined the distribution and chemical characteristics of the redox activity of PM fractions collected in different sites in the Los Angeles Basin. Samples of concentrated coarse, fine, and ultrafine PM, obtained with aerosol concentrators, were studied with regard to their chemical properties and redox activity. Redox activity was highest in the ultrafine fraction, in agreement with results indicating ultrafines were the most potent toward inducing that heme oxygenase expression and depleting intracellular glutathione, which has relevance to induction of oxidative stress. Comparison of the redox activity with chemical composition showed a reasonable correlation of redox activity with elemental carbon (r(2)=0.79), organic carbon (r(2)=0.53), and with benzo[ghi]perylene (r(2)=0.82), consistent with species typically found in mobile emission sources.

UnlabelledThe potential adverse health effects of PM2.5 (particulate matter with an aerodynamic diameter

Ambient concentrations of 15 vapor-and particle-phase (PM2. 5) polycyclic aromatic hydrocarbons (PAHs), listed by the US EPA as priority pollutants, were measured between July 2002 and November 2003 in six Southern California communities participating in a multi-year chronic respiratory health study of schoolchildren. The communities were geographically distributed over two hundred kilometers, extending from Long Beach in coastal Los Angeles, to high mountain areas to the north and west of the Los Angeles basin, and south into Eastern San Diego County. Seasonal and spatial variation in the atmospheric concentrations of PAHs is of interest because this class of compounds includes potent mutagens, carcinogens, and species capable of generating reactive oxygen species (ROS) that may lead to oxidative stress. Naphthalene accounted for 95% of the total PAH mass; annual averages ranged from 89 to 142 ng m-3. Benzo[ghi]perylene (BGP) and the pro-carcinogen benzo[a]pyrene (BAP), present almost exclusively in the particle-phase, ranged respectively from 38 to 231 pg m-3 and 75 and 111 pg m-3, with the highest values observed in Long Beach, a community with a high volume of seaport-related activities, and Lancaster, a commuter dormitory community. A considerable increase in the particle-phase PAH concentration, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM2. 5 averaged 5. 7, reaching 54 at Long Beach. The presented data underscore the importance of seasonal variations on atmospheric PAH concentrations. These observations are relevant to future interpretation and analysis of community-scale human health effects research. [ABSTRACT FROM AUTHOR]

Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were measured in two rural communities (Atascadero and Lompoc) located several hundred km northwest of Los Angeles and in four urban communities 40-100 km downwind of Los Angeles (San Dimas, Upland, Mira Loma, and Riverside), during all seasons, from May 2001 to July 2002. PM 2.5 and vapor-phase PAHs were collected, on prebaked quartz fiber filters and PUF-XAD-4 resin, respectively, at 113 LPM, during 24 h periods, every eighth day, and quantified by HPLC-Fluorescence. At all sites vapor-phase PAHs contained >99.9% of the total PAH mass and were dominated by naphthalene (NAP), which varied from about 60 ng m -3 in Lompoc, a community with light traffic, to ∼580 ng m -3 in Riverside, a community traversed by ∼200,000 vehicles day -1 . During summer pollution episodes in urban sites, NAP concentrations reached 7-30 times annual averages. Except for summer episodes, concentrations of low MW PAHs showed small seasonal variations (∼2 times higher in winter). Similar concentrations of particle-phase PAHs were observed at all sites except for Lompoc. Benzo[ ghi ]perylene (BGP), a marker of gasoline exhaust emissions, showed the highest concentration among particle-phase PAHs, varying from 23.3 pg m -3 in Lompoc to 193 pg m -3 in Mira Loma. Benzo[ a ]pyrene and indeno[ 1,2,3-cd ]pyrene, found exclusively in the particle phase, were much higher in urban sites (∼40-100 pg m -3 ), than in Lompoc (∼12 pg m -3 ). Winter particle-phase PAHs were 2 to 14 times higher than summer levels. Particle-phase PAHs were negatively correlated with mean air temperature in urban sites (r = -0.50 to -0.75), probably resulting from surface inversions occurring during winter. The data suggest that in Southern California vehicular exhaust emissions are a major contributor to particle-phase PAHs. [ABSTRACT FROM AUTHOR]

Abstract: Particulate matter (PM) originating from mobile sources has been linked to a myriad of adverse health outcomes, ranging from cancer to cardiopulmonary disease, and an array of environmental problems, including global warming and acid rain. Till date, however, it is not clear which physical characteristics or chemical constituents of PM are significant contributors to the magnitude of the health risk. This study sought to determine the relationship between physical and chemical characteristics of PM while quantitatively measuring samples for redox activity of diesel and gasoline particulate emissions from passenger vehicles typically in use in Europe. The main objective was to relate PM chemistry to the redox activity in relation to vehicle type and driving cycle. Our results showed a high degree of correlation between several PM species, including elemental and organic carbon, low molecular weight polycyclic aromatic hydrocarbons, and trace metals such as lithium, beryllium, nickel and zinc, and the redox activity of PM, as measured by a quantitative chemical assay, the dithiothreitol (DTT) assay. The reduction in PM mass or number emission factors resulting from the various engine configurations, fuel types and/or after-treatment technologies, however, was non-linearly related to the decrease in overall PM redox activity. While the PM mass emission rate from the diesel particle filter (DPF)-equipped vehicle was on average approximately 25 times lower than that of the conventional diesel, the redox potential was only eight times lower, which makes the per mass PM redox potential of the DPF vehicle about three times higher. Thus, a strategy aimed at protecting public health and welfare by reducing total vehicle mass and number emissions may not fully achieve the desired goal of preventing the health consequences of PM exposure. Further, study of the chemical composition and interactions between various chemical species may yield greater insights into the toxicity of the PM content of vehicle exhaust. [Copyright &y& Elsevier]

As part of the Southern California Particle Center and Supersite (SCPCS) activities, we measured, during all seasons, particle size distributions of 12 priority pollutant polycyclic aromatic hydrocarbons (PAHs), concurrently with elemental carbon (EC), organic carbon (OC), sulfate (SO42-), and nitrate (NO3-) size distributions, from October 2001 to July 2002 in Claremont, CA, a receptor site located about 40 km downwind of central Los Angeles. Samples were collected approximately once every week, for 24-h periods, from midnight to midnight. MOUDI impactors collected samples at 30 LPM which were composited for analysis into monthly periods in three aerodynamic diameter size intervals, defined for the purpose of this work, as: 0–0.18 μm (ultrafine mode), 0.18–2.5 μm (accumulation mode), and 2.5–10 μm (coarse mode). For the monthly composites from October to February, the size distributions of the target PAHs are similar. However, from March to July, notable differences are observed: a significant fraction of the PAH mass is found in the coarse mode, as compared with the previous period. During the entire 1-year period, the form and shape of the EC size distributions did not vary much and are distinguished by prominent mass in the ultrafine and accumulation size mode. For the individual modes of the major species, the highest Pearson''s correlation coefficients for the variation of temperature with species concentration were found in the ultrafine mode for both SO42- (0.92) and EC (0.90), and in the coarse mode for both OC (0.85) and NO3- (0.54). High SO42- correlations are consistent with increased gas-to-particle formation during the warmer months from (precursor) SO2 emissions in the Los Angeles and Lon Beach seaport areas and, similarly for EC, increased atmospheric transport to Claremont as the season progresses from winter to summer. Although not statistically significant, the correlations were negative for the less volatile or particle phase group (log [pLo]⩽-3.22), consistent with increased partitioning from the vapor phase with decreasing temperature. [Copyright &y& Elsevier]