2004 Progress Report: Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB

EPA Grant Number: R827352C013
Subproject: this is subproject number 013 , established and managed by the Center Director under grant R827352
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Southern California Particle Center and Supersite
Center Director: Froines, John R.
Title: Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB
Investigators: Miguel, Antonio
Current Investigators: Miguel, Antonio , Eiguren-Fernandez, Arantza , Sioutas, Constantinos
Institution: University of California - Los Angeles
Current Institution: University of California - Los Angeles , University of Southern California
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2003 through May 31, 2004
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


While epidemiological studies have firmly established that ambient air fine particles (PM2.5) can adversely affect the health of exposed individuals, even at exposure levels at or below the current ambient air standard, several questions regarding fine particle toxicity remain elusive, including: Which chemical component(s) or class of components of fine particulate matter (PM) are the most hazardous? In addition to atmospheric concentration, what other properties of fine PM are important? What role does particle size play in fine PM toxicity? How is the toxicity of fine PM affected as it mixes and reacts with gaseous air pollutants and free-radicals during advective atmospheric transport?

Beginning with the work of Ferin and collaborators (1992), firmly establishing the existence of dramatic differences in pathogenicity resulting from different particle sizes of the same material, laboratory and field studies reported over the last decade firmly demonstrated that the size of atmospheric particles determines: i) the number of particles deposited at a tissue target, ii) where the particles deposit in the human respiratory system, iii) which aerodynamic mechanism governs their deposition in the respiratory tract, and iv) their atmospheric reactivity and life-times.

Clearly then, particle size, concentration, and chemical composition are the aerosol properties among those likely to be most important to both chronic and acute toxicity. Thus, if we want to understand, for regulatory purposes, how toxin-containing airborne particles are transported and transformed, we need to acquire detailed information of their particle size, concentration, and chemical composition, during all seasons of the year, both near their emission sources and in locations where humans are exposed to the airborne aerosol.

The major objective of this research project, complementing other SCPCS activities described elsewhere in this Final EPA report, was to acquire information on the effects of season and location on the concentration, and the size distribution of PAHs (defined by the US EPA as Priority Pollutants) collected in Southern California communities. Detailed size resolution in the ultrafine (Dp<100 nm) and Aitken (Dp<50 nm) size ranges constituted the ultimate foci of these studies.

Progress Summary:

Achievements in Respect to Project Purpose and Objectives

We developed GC-MS and HPLC-selective fluorescence methods to measure all 16 US EPA Priority Pollutant PAHs present in source and ambient air samples (references 1-3). Using the NIST SRM 1649a, which contains certified concentrations for several PAHs, our extraction and quantification procedures provided overall analytical precision of 4.2% and extraction recovery efficiencies ranging from 92 to 97% for all PAHs. We also participated in the development and validation of a GC-MS derivatization-based method used to quantify quinones in diesel exhaust particles, and ambient PM2.5 samples collected in the Los Angeles basin and other Southern California locations (reference 4).

Next, we evaluated the extent of sampling artifacts that might occur during the collection of size resolved semi-volatile and particle-phase PAHs using MOUDI impactors with and without an annular denuder (reference 5).

Between 2001 and 2003, we measured the seasonal and spatial variation of fine particle (PM2.5) and vapor-phase PAHs concentrations at all 12 communities participating in a multi-year chronic respiratory health study of schoolchildren (Children’s Health Study (CHS). The communities were geographically distributed over two hundred kilometers, extending from coastal Central California through coastal Los Angeles, inland to Riverside and San Bernardino counties, and south into Eastern San Diego County (references 6 and 7).

Concurrently with the development and validation of accurate and sensitive methods for PAH quantification, we measured, during all seasons, the 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. Samples were collected from October 2001 to July 2002 in Claremont, CA, a receptor site located about 40 km downwind of central Los Angeles (reference 8).

Our most recent observations of the size distributions of twelve target PAHs in the 10 nm< Dp<2.5 μm size range, showed that, overall, regardless of vapor pressure, the PAH masses in each of the differential fractions (10-18 nm, 18-32 nm, and 32-56 nm) are larger in the smallest fraction (10-18 nm) than that in the two larger fractions (reference 9).

Given our results that naphthalene (identified by the US EPA as a hazardous air pollutant, and is listed in the 2002 State of California’s Proposition 65 program as a substance known to cause cancer) constitutes about 95% of the measured PAH mass, together with several SCPCS researchers, we carried out new field measurements of the naphthalene-to-benzene ratio at the busy Sepulveda Tunnel (under LAX) in Los Angeles, to support an advanced modeling study to quantify population exposure to the emissions of naphthalene throughout Southern California (reference 10).

The studies related to the toxicity of PAHs and quinones, and their concentration in diesel exhaust particles (DEP) used in in vitro experiments (references11-13) are reported in detail elsewhere in this Final Report.

Details of all Significant Technical Aspects of the Project (Both Positive & Negative)

Analytical and Sampling Methods Development. The use of annular denuders was recommended in the literature as a means of reducing “sampling artifacts.” The hypothesis was that, by removing vapor-phase species before particle-phase collection, and then capturing any of the same vapor-phase species that remained after particle-phase collection, the effects of sampling artifacts could be corrected by comparing the levels of the species found associated with the particle-phase and that captured downstream. Our results showed that at a source and a receptor area in the LA Basin, using either sampling system, the size distributions obtained were similar for PAHs found in the particle-phase, but different for the semi-volatiles. At a central Los Angeles site, the largest PAH fraction was found in the 0–0.18 μm, defined here as “ultrafine” size range, typical of primary emissions. At the downwind location, the largest fraction was in the 0.18–2.5 μm accumulation size range, consistent with an “aged” aerosol. We concluded that sampling with the regular MOUDI configuration, i.e., without the use of an annular denuder, is simpler and thus recommended for measurement of the size distribution of PAHs in either group.

Seasonal and Spatial Variations on Vapor- and Particle-Phase (PM2.5) Levels. For all communities, we found that naphthalene (NAP) accounted for 95% of the total PAH mass, with annual averages ranging from 89 to 142 ng/m3. The highest values for benzo[ghi]perylene (BGP), a tracer of light-duty engine exhaust (present almost exclusively in the particle-phase), and of the pro-carcinogen benzo[a]pyrene (BAP) were observed in Long Beach and Lancaster. Annual averages of the pro-carcinogen BAP were also highest in Long Beach and Lancaster (references6 and 7). A considerable increase in the particle-phase PAH level, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM2.5 reached 54 at Long Beach. These data underscore the importance of seasonal variation on PAH concentration, expressed as lower surface and boundary inversion layers and reduced advective atmospheric mixing during the cold season, as compared with the effects of PAH chemical reaction with atmospheric gases and free-radicals during the hot season.

Seasonal Variation of the Size Distribution of PAH, EC and Major Ionic Species Downwind of Central Los Angeles.Samples were collected approximately once every week, for 24-h periods, from midnight to midnight. MOUDI impactors samples were composited for analysis into monthly periods in three aerodynamic diameter size intervals, defined for the purpose of this report, 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 were observed: a significant fraction of the PAH mass was 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 were 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 (r) 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 Long Beach seaport areas and, similarly for EC, increased atmospheric transport to Claremont as the season progressed from winter to summer (reference8).

Observations of PAHs in the Aitken Size Range. Several dynamometer studies reported over the last decade, and more recently, from vehicle-chase studies (David Kittelson’s group in Minnesota), showed that aerosols produced by spark-ignition and diesel engines and by other high-temperature processes contain nanoparticles in the Aitken (Dp<50 nm), nucleation (10<Dp<50 nm), and accumulation mode (50 nm<Dp1<μm), and often, fractal-like particles or agglomerates (Friedlander’s group). Fuel and combustion generated PAHs that accumulate in the engine’s lube oil are normally emitted through the exhaust system. Aitken size range PAHs may result from rapid cooling (self­nucleation) while the hot vapors move along the exhaust pipe into ambient air, or, as hypothesized by McMurry (2004, personal communication) they may partition from the vapor-phase into oily droplets originated from self-nucleated lube oil. While it is still unknown at present, which mechanism(s) contribute to the observed mass in the Aitken size range, our most recent observations of the size distributions of the twelve target PAHs in the 10 nm<Dp<2.5 μm size range, show that, for all target PAHs, regardless of vapor pressure, the masses in each of the differential fractions (10-18 nm, 18-32 nm, and 32-56 nm) are larger in the smallest fraction (10-18 nm) than that in the two larger fractions (reference9). We found that, the masses in the 10-18 nm size bin ranged from 100% for benzo[k]fluoranthene, benzo[a]pyrene, and indeno[1,2,3-cd]pyrene to 46% for anthracene, of the masses collected in the Aitken size range (Dp<56 nm).

Modeling Study to Quantify Population Exposure to the Emissions of Naphthalene Throughout Southern California. Our results (reference10) showed that gasoline and diesel engine exhaust, with related vaporization from fuels, were found to contribute roughly half of the daily total naphthalene burden in Southern California. A more detailed account of this study is reported elsewhere in this Final Report.

Description of Recent Findings, Results, and Conclusions

Caldecott Tunnel Sampling Campaign. As part of Year 6 of our PM Center activities, we measured PM2.5 emission factors, separately for heavy-duty diesel (HDD) and light-duty vehicles (LDV), of volatile, semi-volatile and particle-phase (PM2.5) PAHs, over summer (2004) and winter (2005) periods in the Caldecott tunnel, Berkeley, California. We also obtained size-resolved emission factors for semi-volatile and particle-phase PAHs down to 10 nm Dp. PAH, CO and CO2 samples were collected in Bore 1 (mix of light duty vehicles, LDV and heavy duty diesels, HDD) and Bore 2 (LDV only) of the Caldecott tunnel. Our results (in preparation for publication) showed that total PAH levels (i.e. vapor+particle phase concentration, in ng/m3) were similar in both bores during summer and winter periods, with NAP accounting for 90% of the total PAH mass during both seasons. In general, for PAHs with MW>178 slightly higher concentrations were found during the winter period at both bores, while higher levels of naphthalene, acenaphthene, and fluorene were observed in summer. The most significant difference between Bore 2 and Bore 1 was observed for two of the higher molecular weight PAHs (benzo[g,h,i]perylene, and indeno[1,2,3­cd]pyrene; their concentrations were two times higher in the LDV-only bore.

Using these results, we calculated emission factors (emfs), separately, for LDV and HDD. LDV emfs for total PAHs (vapor+particle phase) are 2 times higher in winter (2005) compared with summer (2004); HDD emfs are three times higher in winter. Emfs for PAHs with molecular weights between 178 and 252 are ca. 4 times higher for HDD while PAHs with MW>252 are practically all emitted by LDVs. Comparing PAH emfs in PM2.5 obtained in summer 2004 with those obtained by in summer 1997 (8 years later), a higher reduction was been observed for HDD as compared with LDV; average reduction emission factors of 6 and 17 were obtained for total PAHs from LDV and HDD, respectively. These results are being written up for submission to publication in the journal Environmental Science & Technology.


A major conclusion of this study is that PAHs found in the Aitken size range represent a previously unreported particle size range, adding a fourth mode to the typical PAH size distributions found in ambient air in the nucleation, accumulation and coarse size modes. In terms of health significance, this finding is important because the increased deposition efficiency in the alveolar area of the human respiratory tract of particles in the 10-32nm diameter range. Particles in this size range may enter cellular and subcellular walls of target eukariotes (references11 and 12).


Ferin J, Oberdorster G, Penney DP. Pulmonary retention of ultrafine and fine particles in rats. American Journal of Respiratory Cell and Molecular Biology 1992;6:535-542.

Resulting publications in peer-review journals.

  1. Pereira P, de Andrade JB, Miguel AH. Determination of 16 priority polycyclic aromatic hydrocarbons (PAH) in particulate matter by HRGC-MS after extraction by sonication. Analytical Sciences 2001;17:1229-1231.
  2. Pereira P, de Andrade JB, Miguel AH. Measurements of semivolatile and particulate polycyclic aromatic hydrocarbons in a bus station and an urban tunnel in Salvador, Brazil. Journal of Environmental Monitoring 2002;4(4):558-561.
  3. Eiguren-Fernandez A, Miguel AH. Determination of semi-volatile and particulate polycyclic aromatic hydrocarbons in SRM 1649a and PM2.5 samples by HPLC-fluorescence. Polycyclic Aromatic Compounds 2003;23:193-205.
  4. Cho AK, Di Stefano E, You Y, Rodriguez CE, Schmitz DA, Kumagai Y, Miguel AH, Eiguren-Fernandez A, Kobayashi T, Avol E, Froines JR. Determination of four quinones in diesel exhaust particles, SRM 1649a and atmospheric PM2.5. Aerosol Science & Technology 2004;38(S1):68-81.
  5. Eiguren Fernandez A, Miguel AH, Jaques P, Sioutas C. Evaluation of a denuder-MOUDI-PUF sampling system to measure the size distribution of semi-volatile polycyclic aromatic hydrocarbons in the atmosphere. Aerosol Science and Technology 2003;37:201-209.
  6. Eiguren-Fernandez A, Miguel AH, Froines JR, Thurairatnam S, Avol E. Seasonal and spatial variations of polycyclic aromatic hydrocarbons in vapor-phase and PM2.5 in Southern California urban and rural communities. Aerosol Science & Technology 2004;38:447-455.
  7. Miguel AH, Eiguren-Fernandez A, Jaques P, Froines JR, Grant B, Mayo P, Sioutas C. Seasonal variation of the particle size distribution of polycylic aromatic hydrocarbons and of major aerosol species in Claremont California. Atmospheric Environment 2004;38:3241-3251.
  8. Eiguren-Fernandez A, Avol EL, Thurairatnam S, Hakami M, Zhu Y, Froines JR, Miguel AH. Seasonal variation greatly influences particle-phase PAH concentrations in Urban Southern California communities. Environmental Science & Technology (In review, 2005).
  9. Miguel AH, Eiguren-Fernandez A, Sioutas C, Fine PM, Geller M, Mayo PR. Observations of twelve USEPA priority polycyclic aromatic hydrocarbons in the aitken size range (10-32nmD). Aerosol Science & Technology 2005;39(5):415-418.
  10. Lu R, Wu J, Turco R, Winer A, Atkinson R, Arey J, Paulson S, Lurmann F, Miguel AH, Eiguren-Fernandez A. Naphthalene distributions and human exposure in the South Coast air basin. Atmospheric Environment 2004;39:489–507.
  11. Li N, Venkatesan I, Miguel AH, Kaplan R, Gujuluva C, Alam J, Nel A. Induction of heme-oxygenase-1 expression in macrophages by diesel exhaust particle chemicals and quinones via the antioxidant-responsive element. Journal of Immunology 2000;3393-3401.
  12. Li N, Alam J, Venkatesan I, Eiguren A, Schmitz D, Di Stefano E, Slaughter N, Killeen E, Wang X, Huang A, Wang M, Miguel A, Cho A, Sioutas C, Nel AE. Nrf2 is a key transcription factor that regulates antioxidant defense in macrophages and epithelial cells: protecting against the proinflammatory and oxidizing effects of diesel exhaust chemicals. Journal of Immunology 2004p;173:3467-3481.
  13. Cho AK, Sioutas C, Miguel AH, Kumagai Y, Schmitz DA, Singh M, Eiguren-Fernandez A, Froines JR. Redox activity of airborne particulate matter (PM) at different sites in the Los Angeles Basin. Environmental Research 2005;99:40-47.

Journal Articles:

No journal articles submitted with this report: View all 14 publications for this subproject

Supplemental Keywords:

RFA, Scientific Discipline, Air, Geographic Area, HUMAN HEALTH, particulate matter, Environmental Chemistry, Health Risk Assessment, Air Pollutants, State, mobile sources, Environmental Monitoring, Health Effects, engine exhaust, ambient aerosol, asthma, motor vehicle emissions, epidemiology, human health effects, automotive emissions, particulate emissions, automobiles, automotive exhaust, air pollution, children, human exposure, diesel exhaust particles, PM characteristics, California (CA), allergens, indoor air quality, aerosols, atmospheric chemistry

Relevant Websites:

http://www.scpcs.ucla.edu Exit

Progress and Final Reports:

Original Abstract
  • 1999
  • 2000
  • 2001
  • 2002 Progress Report
  • 2003 Progress Report
  • Final Report

  • Main Center Abstract and Reports:

    R827352    Southern California Particle Center and Supersite

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827352C001 The Chemical Toxicology of Particulate Matter
    R827352C002 Pro-inflammatory and the Pro-oxidative Effects of Diesel Exhaust Particulate in Vivo and in Vitro
    R827352C003 Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
    R827352C004 Effect of Exposure to Freeways with Heavy Diesel Traffic and Gasoline Traffic on Asthma Mouse Model
    R827352C005 Effects of Exposure to Fine and Ultrafine Concentrated Ambient Particles near a Heavily Trafficked Freeway in Geriatric Rats (Pilot Project)
    R827352C006 Relationship Between Ultrafine Particle Size Distribution and Distance From Highways
    R827352C007 Exposure to Vehicular Pollutants and Respiratory Health
    R827352C008 Traffic Density and Human Reproductive Health
    R827352C009 The Role of Quinones, Aldehydes, Polycyclic Aromatic Hydrocarbons, and other Atmospheric Transformation Products on Chronic Health Effects in Children
    R827352C010 Novel Method for Measurement of Acrolein in Aerosols
    R827352C011 Off-Line Sampling of Exhaled Nitric Oxide in Respiratory Health Surveys
    R827352C012 Controlled Human Exposure Studies with Concentrated PM
    R827352C013 Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB
    R827352C014 Physical and Chemical Characteristics of PM in the LAB (Source Receptor Study)
    R827352C015 Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects
    R827352C016 Particle Dosimetry
    R827352C017 Conduct Research and Monitoring That Contributes to a Better Understanding of the Measurement, Sources, Size Distribution, Chemical Composition, Physical State, Spatial and Temporal Variability, and Health Effects of Suspended PM in the Los Angeles Basin (LAB)