1. Office of Research and Development National Risk Management Research Laboratory/Air Pollution Prevention and Control Division November 6, 2007 Rich Baldauf Health Impacts of Border Crossings Conference May 3, 2012 Mitigation of Near-Road Air Pollution Impacts: Examining Vegetation and other Roadway Design Options

2. 1 Why are we concerned? Public health concerns have been raised regarding population exposures to traffic emissions near large roadways –Adverse health effects for people living, working, and going to school near large roadways, including Asthma Cardiovascular effects Birth and developmental effects Premature mortality –Often highly elevated pollutant concentrations measured –Potentially large population exposed EPA estimates >45 million people in the US live within 100 meters of a major road or transportation facility (from American Housing Survey) Approximately 2 million school children attend classes within 200 meters of a large highway On average, Americans spend >1 hour per day traveling

3. Why are we concerned? Strong international consensus on elevated health risks for near-road populations –Numerous reviews summarized findings of hundreds of studies conducted mainly in the last decade, concluding that exposures to traffic emissions near roads are a “public health concern.” HEI CDC WHO Academic journal review articles –Several public health and medical organizations have made prominent statements regarding these elevated risks CDC American Academy of Pediatrics American College of Cardiology American Public Health Association 2

4. 3 Why are we concerned? Border crossings experience high traffic volumes and idling vehicles, leading to exposures for nearby populations and on-site workers and commuters Public health concerns have raised interest in methods to mitigate these traffic emission impacts –Vehicle emission standards –VMT reduction/alternative transportation options –Buffer/exclusion zones –Use of roadway design and urban planning Road location and configuration Roadside structures and vegetation

5. 4 Why study roadside features? -Few other “short-term” mitigation options -Emission reductions take long to implement (fleet turnover required) -Planning and zoning involved in rerouting/ VMT reduction programs -Buffer/exclusion zones often not feasible -Roadside features are often already present -Roadside vegetation often seen as a positive for other purposes

6. 5 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) Detroit (vegetation)

7. 6 Wind Tunnel Assessments Wind Tunnel Simulation - Six Lane Roadway Noise Barriers Flow

8. Wind Tunnel Assessments Highest concentrations occurred downwind with at-grade sections (no obstructions to air flow) Lowest levels occurred with noise barriers Vegetation effects not analyzed in this study 7

9. Noise Barriers CFD modeling confirms wind tunnel and field results Reductions for populations downwind, but increase in concentrations on the road The higher the barrier, the larger the downwind reductions (but higher concentrations on the road) 8 1H = 6 m No barrier 6 m barrier 18 m barrier (Hagler et al. 2011)

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

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

12. 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)

13. 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 12 (Baldauf et al., 2008a; 2008b)

14. Noise Barriers and Vegetation N3, N4 – hwy + wall + access road N2 –hwy + access road N1– hwy + access road + trees

15. Noise Barriers and Vegetation Vegetation barriers had the lowest downwind pollutant concentrations (although traffic volumes also lower in this neighborhood) Access road behind noise barrier led to increased concentrations Hagler et al. (2010)

16. Noise Barriers and Vegetation Field data: Mobile sampling study at three sites in North Carolina Two sites had tree stands One site had a solid barrier Mebane Raleigh Chapel Hill 15

17. 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)

18. Vegetation Effects Lower size fractions of PM most reduced downwind of the vegetation stand Effect most evident closer to ground-level 17 0 (Preliminary Data: do not cite, quote, or reference)

19. 18 Vegetation Effects Downwind PM and CO generally lower behind vegetation Some conditions may lead to higher levels behind vegetation 0 (Preliminary Data: do not cite, quote, or reference) lllllllllllllllll

20. 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)

21. 20 Vegetation Effects 0 Wind tunnel evaluations investigated PM removal efficiency and mechanisms of removal

22. 21 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 0 0.3 m/s1.5 m/s

23. 22 Vegetation Effects 0 CFD modeling is being conducted at Cornell and the EPA to determine how vegetation affects pollutant transport, dispersion, and removal

24. Stationary and Backpack  ~22-24 hour stationary sampling  ~2 hours backpack sampling  Particulate Matter  Particle count in select size bins (HHPC)  Black carbon (Micro-aethalometer) Mobile Electric Vehicle  ~3 hrs per day (3-4 driving routes)  Particulate Matter  UFP size distributions (EEPS)  Coarse and fine size distributions (APS)  Black carbon (Micro-aethalometer)  Gases  CO (Single Quantum Cascade Laser)  NO2 (tentative) Detroit Vegetation Study

25. On-road and near-road mobile monitoring with varying vegetation and neighborhood configurations Fixed and backpack monitoring for detailed vegetation assessment

26. Vegetation Workshop April, 2010 in RTP, NC Participants: –EPA –USFS –FHWA –States (incl. CARB) –Academic (incl. UC-Davis) –Environmental advocacy –International Summaries –Website –EM article (Jan., 2011) –TRB Session (Jan., 2011) Next Steps –Workshop planned for June 5-6, 2012 in Sacramento, CA http://www.epa.gov/nrmrl/appcd/nearroadway/workshop.html

27. 26 Summary - General Roadside features may provide an opportunity to reduce exposures to traffic emissions for nearby populations –Technique can be implemented in a relatively short time frame –Should be considered in addition to other mitigation options 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

28. 27 Summary - Vegetation Vegetation, in particular, may be an attractive option for near-road air quality mitigation –Studies suggest a reduction in downwind pollutant concentrations –Vegetation provides other advantages, including Aesthetics Water runoff control Shading and energy efficiency Carbon sequestration However, research still needed to quantify the impacts of vegetation –Dimensions of importance (thickness, height, length) –Species differences (including native vs. non-native) –Seasonal differences Other issues must also be considered, including –Increased water consumption –Pathway for pests and invasive species –Fire hazards –Safety issues

29. 28 For More Information Websites: –http://www.epa.gov/airscience/quick-finder/near-roadway.htm –http://www.epa.gov/nrmrl/appcd/nearroadway/workshop.html 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. 2009. J. of Air Quality, Atmosphere, & Health. Vol. 2: 1-9. –Bowker, G.E., R.W. Baldauf, V. Isakov, et al. 2007. Atmos. Environ. 41:8128-8139. –Finn, D., K.L. Clawson, R.G. Carter et al., 2010. Atmos. Environ. 44: 204-214. –Heist, D.K., S.G. Perry, L.A. Brixey, 2009. Atmos. Environ. 43: 5101-5111. Contact Information: Rich Baldauf, PhD, P.E. U.S. Environmental Protection Agency 109 TW Alexander Drive Research Triangle Park, NC 27711 919-541-4386 baldauf.richard@epa.gov