Office of Research and Development National Risk Management Research Laboratory/Air Pollution Prevention and Control Division Rich Baldauf Dec. 19, 2012 Beijing, China Ambient Air Mitigation Strategies for Reducing Exposures to Mobile Source PM 2.5 Emissions

1 Background Reminder: evidence of increased health risks for populations near large roadways Reminder: elevated concentrations of many pollutants near large roads, including PM 2.5 Public health concerns have raised interest in methods to mitigate these traffic emission impacts Transportation and land use planning options include: –Vehicle emission standards and voluntary programs –Reducing vehicle activity/Vehicle Miles Travelled (VMT) –Buffer/exclusion zones –Use of roadway design and urban planning Road location and configuration Roadside structures and vegetation

Vehicle Emission Reductions Reducing emissions from on-road motor vehicles will greatly improve near-road air quality. Examples from the US include: –Light-duty gasoline emission standards (e.g. Tier 2, Mobile Source Air Toxics) –Heavy-duty diesel emission standards (2010 HD Diesel Rule, National Clean Diesel Campaign) Emission programs often take time to implement –Requires fleet turnover or large-scale retrofits –Not necessarily an answer for existing concerns Emission standards focus on tailpipe exhaust –Brake and tire wear, re-entrained road dust still a concern 2

Vehicle Activity Reductions Reducing vehicle activity will lead to lower emissions, improving near-road air quality. Examples of programs to reduce VMT include: –Public transit –Congestion pricing –Pedestrian zones –Telework, alternative commuting programs These programs can have local and regional impacts –The extent of emission reductions can vary widely by program, region, and time of day/year Some programs may shift the locations of emissions, decreasing in some areas but increasing in others 3

Buffer/Exclusion Zone Since near-road concentration gradients tend to be steep, some agencies have recommended limiting development near large roads –California “restricts” new schools being built within 500 ft (~150 meters) of a large roadway (>100,000 AADT highway; >50,000 AADT arterial) Requires extensive environmental review for any new school proposed within 500 ft –CDC recommended that no facilities serving sensitive receptors (schools, daycares, nursing homes, etc.) be developed within 500 ft of a major highway in their “Healthy People 2020” report Since pollutant concentrations drop rapidly, keeping development away from roads will reduce population exposures Limiting development near roads may have unintended consequences 4 - If other land not available, may increase travel distance to access these services - With limited land availability, schools may be located far from the neighborhoods being served, increasing commute time

Buffer/Exclusion Zone Since near-road concentration gradients tend to be steep, some agencies have recommended limiting development near large roads –California “restricts” new schools being built within 500 ft (~150 meters) of a large roadway (>100,000 AADT highway; >50,000 AADT arterial) Requires extensive environmental review for any new school proposed within 500 ft –CDC recommended that no facilities serving sensitive receptors (schools, daycares, nursing homes, etc.) be developed within 500 ft of a major highway in their “Healthy People 2020” report Since pollutant concentrations drop rapidly, keeping development away from roads will reduce population exposures Limiting development near roads may have unintended consequences 5 - If other land not available, may increase travel distance to access these services - With limited land availability, schools may be located far from the neighborhoods being served, increasing commute time

Roadway Design Roadway configuration and the presence of roadside features can affect pollutant transport and dispersion from the road –Roadway configuration reflects design elements that affect the road surface elevation relative to the surrounding terrain Cut/depressed road sections (road bed below surrounding terrain) Elevated fill road sections (road bed above surrounding terrain) Elevated bridge road sections (road bed above surrounding terrain) –Roadside features are structures present near and along the side of the road Noise Barriers/Sound Walls Vegetation Buildings and other infrastructure 6

Roadway Design Effects 7 Wind Tunnel Simulation - Six Lane Roadway Noise Barriers Flow

Roadway Design Effects 8 Heist et al. (2009); Baldauf et al. (2009) Wind tunnel simulations show how roadway design effects pollutant transport and dispersion from the road. Highest pollutant levels and sharpest gradients occur with at- grade and elevated roads

Cut Section Effects Field study in Las Vegas showed highest levels at- grade compared to cut section, although highly variable

Roadside Features - May provide a “short-term” mitigation option - Roadside features are often already present - Roadside features often seen as a positive for other purposes -Noise Reduction -Vegetation benefits (aesthetics, water control, etc.) 10

11 Research Methodology EPA has initiated research to examine the role roadside features (noise barriers, vegetation) may play in reducing near-road air pollutant impacts –Wind tunnel assessments Generalized roadway design scenarios Vegetation removal processes Site-specific configurations in Las Vegas –Computational Fluid Dynamics (CFD) modeling Generalized vegetative and noise barrier scenarios Site-specific configurations in Raleigh and Las Vegas –Field studies Raleigh (vegetation and noise barriers) Idaho (noise barrier tracer study) Detroit (vegetation)

Noise Barriers CFD modeling suggest decreased concentrations downwind of barriers, but increased on-road concentrations Dispersion models being developed to quantify mitigation potential of barriers 12 No barrier 6m barrier 18m barrier (Hagler et al. 2011)

Noise Barrier Effects Tracer studies also indicate noise barriers significantly reduced downwind air pollutant concentrations under all stability conditions Finn et al., (2010) Unstable Stable no barrier barrier

Noise Barrier Effects Noise barrier effects most pronounced when winds from the road Barriers may also trap pollutants, leading to higher on-road concentrations Baldauf et al., (2008a)

Noise Barriers and Vegetation Noise barriers reduced PM levels compared with a clearing Vegetation with noise barriers provided a further reduction of PM concentrations and gradients 15 (Baldauf et al., 2008a; 2008b)

Vegetation Effects Ultrafine PM number count generally reduced downwind of a vegetation stand Higher reductions most often occurred closer to ground-level Variable winds caused variable effects 16 0 Steffans et al. (2011)

Vegetation Effects Lower size fractions of PM most reduced downwind of the vegetation stand Effect most evident closer to ground-level 17 0 Khlystov et al (2012)

Vegetation Effects Lower size fractions of PM most reduced downwind of the vegetation stand Effect most evident closer to ground-level 18 0 Khlystov et al (2012)

Vegetation Effects For thin tree stands, variable results seen under changing wind conditions (e.g. parallel to road, low winds) Future research looking into effects of lower porosity/wider tree stands 19 Hagler et al. (2011)

20 Vegetation Effects Smaller size fractions of PM have higher removal efficiency Removal increases at lower wind velocities Shape and size of branches/leaves affects removal m/s1.5 m/s

Vegetation Workshop Jan., 2008, Davis, CA April, 2010, Durham, NC June, 2012, Sacramento, CA Participants: –EPA –USFS –FHWA –States (incl. CARB) –Academic (incl. UC-Davis) –Environmental advocacy –International Summaries –Website –EM article (Jan., 2011) –TRB Session (Jan., 2011)

22 Roadway Design Effects Roadway configuration and roadside features may provide reductions of exposures to traffic emissions for nearby populations –Roadway configuration could be part of planning process –Roadside features may already exist, or can be implemented in a relatively short time frame Modeling, wind tunnel and field studies highlight the impact of roadside features on nearby air quality –Generally reduce downwind concentrations –May lead to increased concentrations on the upwind side –Variable effects under non-upwind/downwind conditions Consideration of using roadside features will require careful planning –Avoiding gaps or insufficient coverage –Considering effects at edge and top of features Research still needed to quantify the impacts of roadside features –Dimensions of importance (height, length, thickness) –Effects of varying meteorology and topography

23 Summary Multiple options exist to mitigate traffic emission impacts on near-road air quality and population exposures –Reducing emissions –Reducing exposures Ambient air mitigation options focus on exposure reduction although some techniques may also remove air pollutants Each mitigation option has advantages and disadvantages in both short- and long-term air quality improvement and exposure reduction When implementing a strategy for reducing adverse health risks for near-road populations, a combination of these options should be considered

Acknowledgements 24 Academia K. Max Zhang Tom Whitlow David Nowak EPA Sue Kimbrough Gayle Hagler Vlad Isakov David Heist Steve Perry Bill Mitchell James Faircloth Richard Snow Richard Shores Chad Bailey Rich Cook FHWA Victoria Martinez Kevin Black

25 For More Information Websites: – – References –Baldauf, R.W., A. Khlystov, V. Isakov, et al. 2008a. Atmos. Environ. 42: 7502–7507. –Baldauf, R.W., E. Thoma, M. Hays, et al. 2008b. J. Air & Waste Manage Assoc. 58:865–878. –Baldauf, R.W., N. Watkins, D. Heist, et al J. of Air Quality, Atmosphere, & Health. Vol. 2: 1-9. –Bowker, G.E., R.W. Baldauf, V. Isakov, et al Atmos. Environ. 41: –Finn, D., K.L. Clawson, R.G. Carter et al., Atmos. Environ. 44: –Hagler, G.S.W., M-Y. Lin, A. Khlystov, et al Science of the Total Environment –Heist, D.K., S.G. Perry, L.A. Brixey, Atmos. Environ. 43: –Khlystov, A., M-Y Lin, G.S.W. Hagler, et al A&WMA Measurements Workshop, Durham, NC –Steffans, A., K.M Zhang, A. Khlystov et al Atmos. Environ Contact Information: Rich Baldauf, PhD, P.E. U.S. Environmental Protection Agency 109 TW Alexander Drive Research Triangle Park, NC