Office of Research and Development National Risk Management Research Laboratory/Air Pollution Prevention and Control Division November 6, 2007 Rich Baldauf June 5, 2012 Sacramento, CA Examining the Role of Vegetation in Mitigating Near- Road Air Pollution

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

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

3 Why are we concerned? 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 Noise Barriers Roadside Vegetation

4 Why study roadside vegetation? -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 vegetation may already be present -Roadside vegetation often seen as a positive for other purposes

5 Research Methodology EPA and other organizations have initiated research to examine the role roadside vegetation may play in reducing near-road air pollutant impacts –Field studies Research Triangle Park area (vegetation and noise barriers) Detroit (vegetation) –Wind tunnel assessments Vegetation removal processes Site-specific configurations –Computational Fluid Dynamics (CFD) modeling Generalized vegetative scenarios Site-specific configurations

Raleigh Study Results Noise barriers reduced PM levels compared with a clearing Vegetation with noise barriers provided a further reduction of PM concentrations and gradients 6 (Baldauf et al., 2008a; 2008b)

Durham Study Results N3, N4 – hwy + wall + access road N2 –hwy + access road N1– hwy + access road + trees

Durham Study Results 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)

MebaneChapel Hill Noise Barriers and Vegetation Field data: Mobile and fixed site sampling study at two sites in North Carolina –One with primarily pine trees (Chapel Hill) –One with primarily hardwoods (Mebane) 9

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 10 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 11 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 12 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 13 Hagler et al. (2011)

Seasonal Effects After leaf fallBefore leaf fall (Hagler et al., 2012)

15 Wind Tunnel Assessments Wind Tunnel Simulation - Six Lane Roadway Noise Barriers Flow

16 Vegetation Effects 0 Wind tunnel evaluations investigated PM removal efficiency and mechanisms of removal

17 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

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

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

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

21 Summary Vegetation 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, continuity) –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

22 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