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Freeways and Secondary Roadways - something old, something new, something borrowed, something green A discussion for the UC Davis workshop on near roadway impacts and mitigation, January 24, 2007 Thomas A. Cahill Physics Department and the DELTA Group, University of California, Davis

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Freeways and Secondary Roadways -something old, something new, something borrowed, something green

A discussion for the UC Davis workshop on near roadway impacts and mitigation, January 24, 2007

Thomas A. Cahill

Physics Department and the

DELTA Group, University of California, Davis

with the Breathe Calif./SET Health Effects Task Force

Why this sudden interest in secondary roadways?

  • Exacerbation of pre-existing conditions…

    • Increased population and roadway traffic, especially on secondary roads in residential neighborhoods

    • Difficulty of present roadway models to predict near-roadway transport of pollutants in non-ideal conditions

    • Difficulty of traffic models to reflect accurately actual roadway pollutant emissions

  • New dataon

    • Health impacts –

      • near freeway epidemiological studies

      • very fine and ultra fine particle studies

    • Emissions – car exhaust/diesel lube oil

    • Transport – very fine and ultra fine particles, and

    • Mitigation – somethings old, somethings new

  • Study shows how ultrafine particles in air pollution may cause heart disease

    By Rachel Champeau| 1/17/2008 1:00:00 PM

    Patients prone to heart disease may one day be told by physicians to avoid not only fatty foods and smoking but air pollution too.

    A new academic study led by UCLA researchers has revealed that the smallest particles from vehicle emissions may be the most damaging components of air pollution in triggering plaque buildup in the arteries, which can lead to heart attack and stroke.The findings appear in the Jan. 17 online edition of the journal Circulation Research.

    The scientists identified a way in which pollutant particles may promote hardening of the arteries — by inactivating the protective qualities of high density lipoprotein (HDL) cholesterol, known as "good" cholesterol.

    A multicampus team from UCLA, the University of Southern California, the University of California, Irvine, and Michigan State University contributed to the research, which was led by Dr. Andre Nel, UCLA's chief of nanomedicine. The study was primarily funded by the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency (EPA).

    "It appears that the smallest air pollutant particles, which are the most abundant in an urban environment, are the most toxic," said first author Dr. Jesus Araujo, assistant professor of medicine and director of environmental cardiology at the David Geffen School of Medicine at UCLA. "This is the first study that demonstrates the ability of nano-sized air pollutants to promote atherosclerosis in an animal model."

    Nanoparticles are the size of a virus or molecule — less than 0.18 micrometers, or about one-thousandth the size of a human hair. The EPA currently regulates fine particles, which are the next size up, at 2.5 micrometers, but doesn't monitor particles in the nano or ultrafine range. These particles are too small to capture in a filter1 , so new technology must be developed to track their contribution to adverse health effects.

    1Not so. We have been doing this for the past year in Sacramento 13th and T Street and Watt Avenue, with mass, elements, and GC/MS (PAHs, alkanes, sugars, and fatty acids) in 9 size fractions.

    I will give three examples of some relevant work we are doing…

    Example 1. Meshing the extensive 1970s work on freeways and transport with current data

    • Roadway design has a major impact on downwind transport,

    • Downwind transport is dispersion driven, and

    • Urban very fine/ultra fine aerosols are dominated by secondary road emissions, not freeways

      • For fine, US EPA MOBILE - 2/3 diesel, 1/3 cars

      • For fine, CA ARB EMFAC 2007 - 1/3 diesel, 2/3 cars

        Note: Much of the early work is published in the gray literature but not available electronically. I will scan some of this material into the workshop CD.

    Another example of some relevant work in progress…

    Example 2. Studies of heavily traveled secondary roads (Watt Avenue, …) in Sacramento

    • Higher vf/uf impact by 65,000 v/day (1.5% diesel) than by freeway I-5 (170,000 v/day, 10% diesels) – potential reasons….

      • Closer spacing to receptors,

      • Lack of barriers roadway to receptors,

      • Stop and go traffic

      • Dirtier diesels ?

    • Local impact dominated by 3 winter months

    • Organic matter very fine/ultra fine in size and richer in heavy PAHs that diesel exhaust

    The last project is of some work on near-roadway mitigation (later talks)

    Example 3. Mitigation by vegetation – why now?

    • highly efficient lung capture for particles < 0.1 μm

    • Used oil from spark emission vehicles higher in PAHs than from diesel vehicles (Fujita et al, DRI)

    • Major laboratory PAH concentrations in sizes < 0.15 μm

    • Major near roadway ambient heavy PAH (BaP,..) concentrations < 0.1 μm

    • Enhanced deposition velocities for particles < 0.1 μm due to increased diffusion – 15 x at 0.02 μm vs. 0.2 μm

    • Vegetation is an attractive way to get a deposition surface

      Best mitigation: Get the small fraction (circa < 2%) of gross emitting cars off the road!

    Example 1. Meshing the extensive 1970s work on freeways and transport with current data

    • Lead was a unique, conserved, and, we now know, ultra fine tracer of car exhaust

    • There was a major ARB/CalTrans effort 1972 -1974 to understand lead from Los Angeles freeways

    • Our component:

      • 5 LA freeway sites (1 flat, 2 cut, 2 raised section)

      • 120 transects, each with

        • 2 hr resolution, day and night,

        • 5 size modes,

        • Full elemental analysis > sodium

        • Line source modeled concentrations

    Los Angeles CA US

    Sponsored Links

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    1973 - at grade

    1973 - cut section

    1973 fill section

    Zhu et al 2002

    Results for the Santa Monica freeway – also used by US EPA for their model

    Lateral transport from freeways: theory, lead from at grade and from cut (depressed) freeway configurations

    Lateral transport of ultra fine particles – efficient transport, no coagulation!


    Lateral transport at grade

    What was the effect of the two upwind freeways?

    • Assume 8 km upwind

    • Assume “sliding box” mixed cell = 4 m

    • Assume LA inversion = 400 m

    • Assume no coagulation, settling, etc.

    • Then = Concentration ~ 1% of freeway peak

    • Even adding the San Diego freeway,, no more than a few % from freeways.

    • Actual upwind value circa 15% of near roadway peak

    • Thus, circa ¾ BC and particle number from non-freeway sources

      Note: ARB EMFAC ~ 2/3 cars, 1/3 diesels

    January 6, 2007

    And more ….Check the distances: < 530 m, <1060 m, 1060 m to 1600 m, > 1600 m

    Lateral transport – at grade, cut and fill – no trees or barriers

    Lead 10 g/m3, 24 hr

    Size and composition of diesel aerosols, including ultra fines (U. Minn./DRI/UC Davis)

    Roadway studies of diesel and auto emission rates

    California CERC and Nevada DRI laboratory data

    HEI Tuscarora PA tunnel study freeway studies

    CA Air Resources Board studies of freeway ultra fines

    Breathe California (ex- Amer. Lung Assoc) studies of secondary roadways in Sacramento

    Toxicity of used diesel and spark emission vehicle

    Lubricating oils - Nevada Desert Research Inst.

    EPA Region IX/ASU/UC Davis organics, trucks, trains, and cars

    New information – vehicular emissions

    U. Minn. Dynamometer Diesel tests; DRI mass and sulfates, DELTA Group S and elements


    Lube oil



    U. Minnesota Dynamometer Diesel Tests; same California fuel, different engine – no mention of smoke

    Lube oil

    Average Zn to mass, all DRI tests, 1800  1300

    New information on the toxicity of car exhaust

    • There is evidence that spark emission car exhaust has more heavy PAHs than diesel truck/bus exhaust

      • Theory of PAH formation makes small cylinder vehicles worse than large cylinder vehicles

        • Temperature of formation for PAHs is low, < 600 C

        • Higher cylinder wall to volume ratio, cars vs trucks

      • Gertler at al 2002 had the benzo-a-pyrene emission rates roughly the same per vehicle, cars vs trucks, for the HEI Tuscarora Tunnel Study

      • We find relatively high ultra fine mass from the lubricating oil in CNG busses, ~ ¼ diesel busses

      • Eric Fujita at Desert Research Institute showed used spark emission lubrication oil was 10 to 20 times higher in PAHs than used diesel oil

    Typical daytime traffic 50 m south of sampling site

    Cars have more PAHs in their oil than diesels

    Del Paso Manor

    Arden Middle School

    Sacramento CDS

    ARB 13th and T

    Example #2: Arden Middle School at Watt Avenue – 65,000 v/day, > 98% cars

    Watt Avenue

    Arden Middle School

    Sebastian Way

    Watt Ave Traffic - 15 m from school: No mitigation by road configuration possible

    HETF data unexpected fine mass – mis-tuned natural gas water heater – fixed in 30 min!

    Figure 15 PM2.5 mass and 3 sub components, Arden Middle School site

    Result – Very fine/ultra fine mass at Arden Middle School

    Gertler et al 2002 cars and trucks

    Using Zn ratio from DRI diesels




    Mass in the finer fractions

    Comparison of composition: Arden Middle vs. Roseville rail yard

    Surprise! Vanadium is most likely associated with bunker oil combustion from ships in the port of Oakland.

    PM2.5 Sac. 13th and T, Jan - Mar, 2007


    PM2.5 Del Paso Manor, Jan - Mar, 2007


    Even size and time resolved aerosols track across 4 miles of Sacramento (wood smoke)

    PM2.5 Del Paso Manor, Mar - May, 2007

    Spring B

    Spring A

    Trestle fire

    Surprise! Upwind and downwind are essentially equivalent (TMC, ASU in progress)

    Car exhaust dominates Watt Avenue PAH concentrations

    Benzo{a}pyrene ~ 1/4

    Example #3: Mitigation via vegetative capture - theory

    • Very fine (< 0.25 m) and ultra fine (< 0.1 m) diameter particles have suspected health impacts via several mechanisms including -

      • Insoluble ultra fine particles in the lung and heart

      • Carcinogens in the lung

    • Very fine (< 0.25 m) and ultra fine (< 0.1 m) diameter particles have relatively high removal rates via diffusion if a surface is close

    • Vegetation can provide such a surface

    Bottom line:

    Very fine and ultra fine particles can be preferentially removed by diffusion to surfaces

    “To separate the effect of the planting from the freeway configuration would be a great mistake” (Cahill et al, ARB 502,1974)

    • “The embankments of the cut section freeways were heavily planted.”

    • The Santa Monica cut-section site had “a dense thicket of bushes ~ 20 feet high at the crest of the embankment hard against the right of way fence.”

    • The Harbor cut section freeway site “ was similarly planted, with eucalyptus and bushed extending higher than 30 feet on the downwind site”

    • “The thickets were quite dense, and effectively cut the wind in their lee.”

    UC Davis Mechanical Engineering 20 m wind tunnel

    Size distribution of flare aerosols – scaled to tunnel wind velocity

    Test in progress: Erin is watching the readout of wind velocity

    Mitigation of very fine and ultra fine particles by vegetation (preliminary: ongoing HETF project)

    Wind velocity (mi/hr)

    Removal of very fine particles

    Conclusions – wind tunnel vegetative capture studies

    • Typically 75% of very fine particles 0.26 to 0.09 m are removed by 2 m of vegetation at 1 mi/hr wind velocity.

    • Calculations indicate 95% removal of ultra fine particles in the same situation.

    • This process becomes inefficient with wind velocities above 3 mi/hr

    • Redwood and deodar are better than live oak.

    Chui adding oleander branches

    Very preliminary – branches versus empty box

    With vegetative barriers on both sides (and ideally the median) of roadways, one benefits by -

    • At high and medium wind velocities, turbulence mixes and lofts roadway pollutants

    • At medium and low wind velocities, the barriers slow lateral transport and allow vehicular waste heat to loft pollutants

    • At low wind velocities, very fine and ultra fine particles will be captured as they migrate through the semi-transparent barriers.

    Mitigation options – we must move in parallel on all of them!

    • Roadway source improvements, including

      • Cleaner engines, fuel, and new artificial lubricating oils

      • Removal of gross emitting vehicles ( ~ 3%) from roadways (worst 1% vehicles =  30% of vf/uf mass)

      • Reduced traffic via transportation alternatives

  • Roadway design options – “Complete Streets”

    • Highway design; cut section, tunnel (cleaned!)

    • Pollution barriers – use waste heat and vegetation to loft and trap uf particles (walls alone don’t work)

  • Reduced Transport efficiency to residences

    • Distance! This should be a key factor in new roads.

    • Pollution barriers, especially vegetation

  • Residential indoor air quality improvement

    • Positively pressurized filtered receptors

  • Opportunities for new directions

    • Add spark emission vehicle particulates to California's Proposition 65 Toxic Air Contamination roster?

      • Not likely, I am told by those who know

    • On road sensing for smoking cars and the means to remove them from the highways

      • Worth an effort; we (BC/SET) already helped add smoke sensing to the inspection program last year.

    • A new very fine or ultra fine mass standard

      • Relatively easy implementation

      • Uses existing filter – mass infrastructure

      • Avoids routine expensive organic speciation (archived)

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