Final Report: Sources, Composition, Variability and Toxicological Characteristics of Coarse (PM10-2.5) Particles in Southern California

EPA Grant Number: R833743
Title: Sources, Composition, Variability and Toxicological Characteristics of Coarse (PM10-2.5) Particles in Southern California
Investigators: Sioutas, Constantinos , Cho, Arthur K. , Froines, John R. , Moore, Katharine F. , Nel, Andre E. , Schauer, James J.
Institution: University of Southern California , University of California - Los Angeles , University of Wisconsin - Madison
EPA Project Officer: Chung, Serena
Project Period: November 1, 2007 through October 31, 2009 (Extended to October 31, 2012)
Project Amount: $1,120,641
RFA: Sources, Composition, and Health Effects of Coarse Particulate Matter (2006) RFA Text |  Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter

Objective:

The objective of this study is to provide the much-needed information on the relationships between coarse particulate matter (CPM) sources, spatial and seasonal characteristics, and toxicity in Southern California. The multidisciplinary research currently under way combines ambient measurements, exposure assessment and toxicology. The results of this study – the Los Angeles Basin (LAB) Coarse PM Study – will be integrated with other major research efforts currently under way in Southern California, including the EPA-funded Southern California PM Center.

Summary/Accomplishments (Outputs/Outcomes):

The time-integrated mass concentration results indicate that ambient coarse PM varies from 0.5 µg/m3 to more than 35 µg/m3 at the 10 sites in the Los Angeles basin. Mean 24-hour coarse PM concentrations at all sites are typically 10 µg/m3 with the exception of Lancaster site, where the average concentration is about half (5 µg/m3). Summer concentrations were typically 2 to 4 times higher than the winter concentrations at most sites. However, summer concentrations in Long Beach were lower than in the winter. Concentrations derived from both of the samplers used in this study (PCIS and USC VI) were compared to each other at 9 of the 10 outdoor monitoring sites. Agreement in the coarse PM concentrations produced by these two samplers is very reasonable (within 15% on average) with PCIS concentrations typically lower.

CPM concentration correlations between different sites reveal similar trends of CPM concentrations in nearby sites. The Long Beach site, which is located in the “source” regions of Los Angeles basin, had weak correlations with other sites, while strong correlations were observed among the urban Los Angeles sites. Correlations between measured CPM and PM2.5 were investigated. PM2.5 particles are produced predominantly from vehicular emissions and high correlations indicate that the dominant source of coarse particles is traffic-induced resuspended PM in urban areas, where correlations were relatively higher. The relatively lower correlations in rural sites indicate that wind-blown dust is the significant contributor to CPM concentrations. Correlation of CPM and PM2.5 concentrations is much higher during winter than summer, highlighting the increasing role of windblown dust in windier and drier months in summer.

To characterize the chemical composition of coarse particles, chemical constituents are divided into five major categories: 1) crustal materials and trace elements; 2) organic matter; 3) elemental carbon; 4) sea salts; and 5) secondary ions. Overall, crustal materials and trace elements were the most dominant sources of coarse PM in this Basin, followed by secondary ions and organic matter. In particular, nitrate was the most abundant inorganic species and accounted for more than 17% of total reconstructed mass. Concentrations of elemental carbon were low in the coarse mode, with an average mass fraction of less than 2% across sites. Higher concentrations of sea salt were observed at the coastal sites, while crustal materials became dominant inland. The two Riverside sites experienced higher levels of organic matter, probably generated from the nearby agricultural area. Interestingly, organic carbon (OC) was found to be highly correlated with soil dust tracers, suggesting that organic materials and mineral dust might share common origins or that organic materials might be present on the surface of mineral dust particles in the coarse mode.

The abundance and the spatial and temporal behavior of metals in coarse fraction of atmospheric particulate matter (CPM, particles smaller than 10 and larger than 2.5 µm in diameter, PM10-2.5) were studied in the Los Angeles area. Major trace element and metal sources contributing to CPM may consist of (but not limited to) re-suspended road dust, industrial materials, brake linings, tire residues, catalytic converter tracers, sea salt spray, etc. Trace metals in CPM showed distinct seasonal and temporal variations depending on the particle source from which they originate. In order to identify the sources of trace metal content of CPM a principal components analysis (PCA) was performed. Five principal components of inter-correlated trace metal species were identified (crustal metals, abrasive vehicular emissions, abrasive mechanical planarization, catalyst converter material and sea salt), explaining 78.3% of total variance of CPM metal content. Mineral material, closely correlated with some of the rare earth elements, were identified as the main contributor to overall CPM mass, which accounts for 33.2% total CPM metal content, followed by abrasive vehicular tracers and noble metals from catalytic converters. The concentration of the abrasive vehicular tracers was correlated closely across over two orders of magnitude, which is seen as evidence that major portions of transition metals (Cu, Ba, Fe, Sb) are released through abrasive vehicular emissions, particularly the wear of brake linings. To better understand the sources of these metal species, their temporal and spatial variations (in each identified class), were investigated with regards to the proximity of each site to major CPM sources. This yields a comprehensive data set for Los Angeles metropolitan airborne trace metals and their sources.

To investigate how atmospheric and meteorological parameters (including wind speed and direction, temperature, relative humidity, mixing height, etc.) influence the ambient coarse PM concentrations and composition, three sampling sites were set up in the Los Angeles Basin to collect coarse PM in four distinct time periods of the day (morning, midday, afternoon and overnight) in summer 2009 and winter 2010. The diurnal profile of chemical components and constituents of coarse PM differs significantly in the two seasons examined. In summer, highest levels of CPM mass, crustal materials and trace elements, vehicle abrasion, and water soluble organic carbon were observed in midday and/or afternoon when the wind speed was higher at the three sampling sites. In winter, the basin was characterized by stagnation conditions with low atmospheric dilution, and vehicle-induced turbulence became an important particle re-suspension mechanism when mixing height was low, as highlighted by the high levels of coarse PM mass, as well as mineral and road dust in the winter overnight period at the near freeway sampling sites. Nitrate was formed predominantly by sea salt depletion in summer, while the reactions with mineral dust particles, as well as the condensation of ammonium nitrate on PM surfaces also contributed to the formation of nitrate in winter, when sea salt levels were low.

The generation of reactive oxygen species (ROS) was used to evaluate the toxic activity of coarse particles. The diurnal variability of coarse PM-induced oxidative potential and the specific coarse PM sources / species that drive the ROS activity were determined using data from the intensive study. Overall, the diurnal profile of ROS activity was different in summer and winter. ROS activity peaked in summer midday / afternoon when wind speed was higher, while higher ROS activity was observed overnight in winter when traffic-induced turbulence became the primary re-suspension mechanism. Although abundant, crustal materials experienced very low water solubility and were not highly correlated with ROS activity. On the other hand, elements of anthropogenic origins such as Ba, Zn and Cu showed moderate solubility. Although relatively low in mass fraction, water-soluble V, Pd, Cu and Rh, primarily of anthropogenic origins, experienced high associations (R2 > 0.60) with ROS activity.

Conclusions:

The results of this study have become a significant resource towards the development of a fundamental understanding of the sources and formation mechanisms of ambient coarse particles in Southern California, and will help to provide a strong scientific foundation to develop more effective regulatory strategies for coarse particles. Contrasting to the anthropogenic origins of fine particles, CPM predominantly arises from natural sources including crustal and biological materials, as well as fresh and aged sea salt. In particular, our results indicate that emissions from soil and the associated biota constitute the majority of the organic content in the coarse size fraction. Although the levels of crustal materials and organic matter experienced seasonal variations, their relative contributions to CPM mass were similar throughout the year, suggesting the source strength of soil dust and the associated biota is not much affected by the seasonal variation of meteorological conditions. In contrast, the levels and the fractions of sea salt (both fresh and aged) experienced seasonal variations, with higher levels in spring and summer when the prevailing onshore winds transported marine aerosols from coast to inland. The diurnal variation of coarse PM chemical composition is pronounced. In summer, the levels of CPM mass, mineral and road dust, and WSOC were highest in the midday / afternoon, concurrent with the high wind speeds. In winter, the concentrations of mineral and road dust, sea salt and inorganic ions peaked overnight, when atmospheric dilution was low and turbulences from vehicular motions became a dominant re-suspension mechanism of coarse particles. Using oxidative potential as a metric to evaluate toxicity, constituents that drive ROS activity of CPM (mainly water soluble Cu) are mainly anthropogenic in origin, and their contributions to CPM mass are low. Hence, mass-based PM standards may not be effective in controlling the sources that drive ROS activity in coarse particles. Based on the results of this investigation, it is recommended to regulate coarse particles using target controls. Prioritizing the critical PM sources that are responsible for inducing adverse health effects may be the most effective approach to protect the public health from CPM exposure. 


Journal Articles on this Report : 12 Displayed | Download in RIS Format

Other project views: All 21 publications 12 publications in selected types All 12 journal articles
Type Citation Project Document Sources
Journal Article Cheung K, Daher N, Kam W, Shafer MM, Ning Z, Schauer JJ, Sioutas C. Spatial and temporal variation of chemical composition and mass closure of ambient coarse particulate matter (PM10-2.5) in the Los Angeles area. Atmospheric Environment 2011;45(16):2651-2662. R833743 (2010)
R833743 (2011)
R833743 (Final)
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  • Journal Article Cheung K, Daher N, Shafer MM, Ning Z, Schauer JJ, Sioutas C. Diurnal trends in coarse particulate matter composition in the Los Angeles Basin. Journal of Environmental Monitoring 2011;13(11):3277-3287. R833743 (2011)
    R833743 (Final)
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  • Journal Article Cheung K, Shafer MM, Schauer JJ, Sioutas C. Diurnal trends in oxidative potential of coarse particulate matter in the Los Angeles Basin and their relation to sources and chemical composition. Environmental Science & Technology 2012;46(7):3779-3787. R833743 (2011)
    R833743 (Final)
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  • Journal Article Cheung K, Shafer MM, Schauer JJ, Sioutas C. Historical trends in the mass and chemical species concentrations of coarse particulate matter in the Los Angeles Basin and relation to sources and air quality regulations. Journal of the Air & Waste Management Association 2012;62(5):541-556. R833743 (2011)
    R833743 (Final)
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  • Journal Article Cheung K, Olson MR, Shelton B, Schauer JJ, Sioutas C. Seasonal and spatial variations of individual organic compounds of coarse particulate matter in the Los Angeles Basin. Atmospheric Environment 2012;59:1-10. R833743 (Final)
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  • Journal Article Li N, Wang M, Barajas B, Sioutas C, Williams MA, Nel AE. Nrf2 Deficiency in dendritic cells enhances the adjuvant effect of ambient ultrafine particles on allergic sensitization. Journal of Innate Immunity 2013;5(6):543-554. R833743 (Final)
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  • Journal Article Moore KF, Verma V, Minguillon MC, Sioutas C. Inter-and Intra-community variability in continuous coarse particulate matter (PM10-2.5) concentrations in the Los Angeles area. Aerosol Science and Technology 2010;44(7):526-540. R833743 (2009)
    R833743 (2010)
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    R831697 (Final)
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  • Journal Article Pakbin P, Hudda N, Cheung KL, Moore KF, Sioutas C. Spatial and temporal variability of coarse (PM10-2.5) particulate matter concentrations in the Los Angeles area. Aerosol Science and Technology 2010;44(7):514-525. R833743 (2009)
    R833743 (2010)
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    R831697 (2013)
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  • Journal Article Pakbin P, Ning Z, Shafer MM, Schauer JJ, Sioutas C. Seasonal and spatial coarse particle elemental concentrations in the Los Angeles area. Aerosol Science and Technology 2011;45(8):949-963. R833743 (Final)
    R831697 (2013)
    R831697 (Final)
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  • Journal Article Polidori A, Cheung KL, Arhami M, Delfino RJ, Schauer JJ, Sioutas C. Relationships between size-fractionated indoor and outdoor trace elements at four retirement communities in southern California. Atmospheric Chemistry and Physics 2009;9(14):4521-4536. R833743 (Final)
    R832413 (2009)
    R832413 (Final)
    R832413C001 (2009)
    R832413C001 (Final)
    R832413C004 (2009)
    R832413C004 (2010)
    R832413C004 (Final)
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  • Journal Article Saffari A, Daher N, Shafer MM, Schauer JJ, Sioutas C. Global perspective on the oxidative potential of airborne particulate matter: a synthesis of research findings. Environmental Science & Technology 2014;48(13):7576-7583. R833743 (Final)
    R832413 (Final)
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  • Journal Article Wang DB, Kam WN, Cheung K, Pakbin P, Sioutas C. Development of a two-stage virtual impactor system for high concentration enrichment of ultrafine, PM2.5, and coarse particulate matter. Aerosol Science and Technology 2013;47(3):231-238. R833743 (Final)
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  • Supplemental Keywords:

    Air pollution, ambient air quality, monitoring, environmental exposure, toxicology, human health, sensitive populations, environmental monitoring, air sampling, airborne particulate matter, chemical characteristics, chemical speciation sampling, source apportionment, mineral and road dust, vehicular abrasive emission, oxidative potential
     
    , RFA, Scientific Discipline, Air, particulate matter, Health Risk Assessment, Biology, atmospheric particulate matter, PM10, atmospheric particles, cardiopulmonary responses, human health effects, bioavailability, cardiovascular vulnerability, cardiotoxicity, coarse pm, exposure assessment

    Relevant Websites:

    The USC Aerosol Laboratory web-site describing the on-going activities of Dr. Sioutas’ research group is available at http://www.usc.edu/aerosol/ Exit

     

    Progress and Final Reports:

    Original Abstract
  • 2008 Progress Report
  • 2009 Progress Report
  • 2010 Progress Report
  • 2011 Progress Report