2003 Progress Report: Relationship Between Ultrafine Particle Size Distribution and Distance From Highways

EPA Grant Number: R827352C006
Subproject: this is subproject number 006 , 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: Relationship Between Ultrafine Particle Size Distribution and Distance From Highways
Investigators: Hinds, William C. , Sioutas, Constantinos , Zhu, Yifang
Institution: University of California - Los Angeles , University of Southern California
EPA Project Officer: Hunt, Sherri
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2002 through May 31, 2003
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


The overall objective of this project is to improve our knowledge of the indoor levels of ultrafine (UF) particles from outdoor origin, especially those from motor vehicles in the vicinity of freeways.

Previously, we have reported high concentrations of UF particles near major freeways. Many urban residences are located in close proximity to high-density roadways. Given that people spend more than 80 percent of their time indoors, understanding transport of UF particles from outdoor to indoor environments is important for assessing impacts of outdoor particulate matter (PM) on human health. The extent of particle penetration into indoor environments is governed by indoor and outdoor sources, exchange rates, and particle physicochemical characteristics. Indoor particle concentrations, therefore, depend on the dynamics of the transport and fate of outdoor particles in the indoor environments. Previous research in this area has focused on PM2.5 and PM10 properties and behavior (Jones, et al., 2000; Thatcher and Layton, 1995). These studies found outdoor particles to be present at significant concentrations in indoor spaces. Considering health implications of UF particle exposure, it is important to assess the particles’ penetration characteristics into indoor environments and the relationship between their physical and chemical properties and infiltration.

This is one of the project progress reports for the SCPCS. The progress for the other research projects conducted by the Center is described in separate reports (see R827352 through R827352C010 and R827352C012 through R827352C021).

Progress Summary:

Four apartments near the 405 Freeway in Los Angeles were recruited for this study. Three of the apartments (Apt 1, 2, and 3) are on the eastern side of the 405 Freeway. They are on the third floor with windows 3 m above a sound barrier wall. The horizontal distances between apartments 1-3 and the wall range from 15 m to 40 m. The fourth apartment (Apt 4) is on the opposite, western side of the 405 Freeway, 15 m from the sound barrier wall. Apt 4 is on the second floor with windows 0.5 m above the wall. All of the apartments are about 8 years old with central mechanical ventilation systems that can be turned off. Figure 1 illustrates the location of the sampling site, with relative distances and positions of the four study apartments and the 405 Freeway.

Schematic Diagram of Sampling Site and Dominant Wind Directions

Figure 1. Schematic Diagram of Sampling Site and Dominant Wind Directions

Indoor and outdoor UF particle size distributions (6 nm to 220 nm) were measured concurrently under different ventilation conditions without indoor sources or aerosol generation activities. Figures 2 shows averaged particle size distributions and indoor/outdoor (I/O) ratios for Apt 1. Figure 2a shows daytime (10 a.m.-5 p.m.) and Figure 2b shows nighttime indoor and outdoor particle size distributions, with the x- and y-axes indicating particle diameter (nm) and particle number concentration (PNC) as dN/dLogDp (cm-3), respectively. Figure 2c shows size dependent I/O ratios during day- and nighttime.

Figure 2a shows a daytime outdoor particle size mode near 20 nm, consistent with previous reports (Zhu, et al., 2002b). No such mode exists for indoor observations, and indoor PNC is much more stable than outdoors. Nighttime PNCs, shown in Figure 2b, are comparable to their daytime values. Although traffic densities are lower during the night, vehicle speeds on the freeway are much faster. It has been shown previously that faster vehicles generate more particles (Zhu, et al., 2002b). Lower nighttime temperatures also may result in higher emission factors for particle number, as described by Kittelson (1998). Another reason for higher PNCs during the night may be lower wind speeds and a lower atmospheric mixing height, thus weaker atmospheric dilution effects.

As Figure 2c shows, I/O ratios during day- and nighttime exhibit similar trends and shapes. Day and night I/O profiles for particles above 20 nm are consistent with theoretical curve shapes.

Schematic Diagram of Sampling Site and Dominant Wind Directions

Figure 2. Averaged (a) Daytime and (b) Nighttime Outdoor and Indoor Particle Size Distri butions and (c) Size Dependant I/O Ratios in Apt 1

Curves for particles below 20 nm do not correspond to the accepted theory, as no downward trend is observed for both day- and nighttime observations. One possible reason is the low instrument detection limit in that size range, and thus large variability and less statistical confidence in data blow 20 nm. Another possible reason may be the unique, semivolatile, nature of freeway UF particles. Theories always assume particles are 100 percent nonvolatile. Although this may be true for most previous studies conducted under urban background conditions, freshly emitted freeway UF particles are known to have a considerable fraction of volatile components, especially particles below 50 nm (Kittelson, 1998). For example, some of the particles in the 20-40 nm size range may lose their volatile components and become particles of 20 nm or less. Such loss of volatile components has been observed previously (Lunden, et al., 2003). The difference between day and night I/O may be a result of higher air exchange rates during the daytime.

Future Activities:

Because exposure assessment for UF PM will require detailed site-specific data, microenvironment data, or the use of concentration models, the objective of Year 6 of the project is to improve our knowledge of the spatial and temporal distribution of UF PM. The basic hypothesis is that locations with high concentrations of UF PM can dominate an individual’s daily dose of UF PM in urban areas. We propose the following projects in Year 6: (1 ) spatial profiles of UF PM near freeways at night; (2) UF PM concentrations inside and outside vehicles driving on freeways; (3) UF PM exposure on or near busy streets; and (4) measurement of UF PM near freeways over a wider range of ambient temperatures than previous measurements.


Jones NC, Thornton CA, Mark D, Harrison RM. Indoor/outdoor relationships of particulate matter in domestic homes with roadside, urban and rural locations. Atmospheric Environment 2000;34(16):2603-2612.

Kittelson DB. Engines and nanoparticles: a review. Journal of Aerosol Science 1998;29(5-6):575-588.

Lunden MM, et al. The transformation of outdoor ammonium nitrate aerosols in the indoor environment. Atmospheric Environment 2003;37(39-40):5633-5644.

Thatcher TL, Layton DW. Deposition, resuspension, and penetration of particles within a residence. Atmospheric Environment 1995;29(13):1487-1497.

Zhu Y, Hinds WC, Kim S, Shen S, Sioutas C. Study of ultrafine particles near a major highway with heavy-duty diesel traffic. Atmospheric Environment 2002a;36(27):4323-4335.

Zhu Y, Hinds WC, Kim S, Sioutas C. Concentration and size distribution of ultrafine particles near a major highway. Journal of the Air and Waste Management Association 2002b;52(9):1032-1042.

Zhu Y, Hinds WC, Shen S, Sioutas C. Seasonal trends of concentration and size distribution of ultrafine particles near major highways in Los Angeles. Aerosol Science and Technology (accepted, 2003).

Journal Articles:

No journal articles submitted with this report: View all 13 publications for this subproject

Supplemental Keywords:

particulate matter, PM, quinones, polycyclic aromatic hydrocarbons, PAHs, aldehydes, ketones, metals, allergic airway disease, human exposure studies, asthma, cardiovascular effects, aerosol sampling, atmospheric aerosol, environmental monitoring, environmental statistics, California, CA, acute exposure, aerosols, air pollution, air quality, air toxics, airway disease, allergen, allergic response, ambient aerosol, assessment of exposure, asthma triggers, atmospheric chemistry, bioaerosols, biological response, childhood respiratory disease, children, dosimetry, environmental hazard exposures, environmental health hazard, environmental triggers, environmentally caused disease, epidemiology, exposure assessment, health effects, home, household, human exposure, human health effects, indoor air quality, inhaled particles, lead, outdoor air, particle concentrator, particle transport, particulate exposure, particulates, sensitive populations, toxicology, toxics,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, Geographic Area, particulate matter, Environmental Chemistry, Health Risk Assessment, State, Risk Assessments, Biochemistry, mobile sources, Physical Processes, engine exhaust, atmospheric particulate matter, urban air, motor vehicle emissions, atmospheric particles, automotive emissions, particulate emissions, airway disease, automobile exhaust, exposure, automobiles, automotive exhaust, diesel exhaust, air pollution, air sampling, human exposure, ultrafine particulate matter, diesel exhaust particles, frreway study, PM, PM characteristics, California (CA), airborne urban contaminants

Relevant Websites:

http://www.scpcs.ucla.edu/exit EPA

Progress and Final Reports:

Original Abstract
  • 1999
  • 2000
  • 2001 Progress Report
  • 2002 Progress Report
  • 2004 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)