Green infrastructure as a tool to mitigate local air pollution and SLCPs from transport

Richard Baldauf, U.S. Environmental Protection Agency

CCAC Webinar Series

July 21, 2022

Office of Research and Development

National Risk Management Research Laboratory/Air Pollution Prevention and Control Division

Introduction

Interest in planting more trees and providing more urban green space has grown in recent years

• Global planting programs such as the Trillion Trees Initiative
• Regional and local climate adaptation and resilience projects for stormwater management, urban cooling, and CO2 sequestration

Recent research shows that urban green infrastructure can also impact local air pollution and mitigate select SLCPs

• Promoting urban vegetation can have multiple benefits on climate change mitigation, air quality, and improved public health

Programs are underway to integrate air pollution and SLCP mitigation into urban green infrastructure planning, including:

• U.S. EPA and the Polish Ministry of Climate bilateral agreement projects
• Planning for air pollution mitigation at the Port of Lima/Callao in Peru
• Projects in Europe including from the Horizon 2020 iSCAPE project
• Active and planned projects in the U.S. including Atlanta, Chicago, Dallas, Detroit, Louisville, and Oakland/San Francisco

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Short-Lived Climate Pollutants Effects

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Air Pollution Health Effects

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People living, working and going to school near highways and large transportation facilities face increased health risks

Other studies have also linked other adverse effects including:

• Childhood leukemia
• Cognitive development
• Neurological disorders including autism

Health Concerns from Transport

Air pollution and exposures often highly elevated near large transportation sources, especially within first 200-300 meters

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Karner et al. 2010, Environ Science & Tech, 44(14), pp.5334-5344

Health Concerns from Transport

Transport Mitigation Options

Mitigating transport emissions, exposures, and health effects can be achieved by multiple strategies:

• Reducing vehicle direct emissions
• Reducing vehicle use and activity
• Reducing ambient air concentrations through urban and transportation development
• Increasing urban green infrastructure and green space

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How Urban Vegetation Mitigates Air Pollution

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• PM number reductions as high as 50%; black carbon reduced as high as 25%
• Plant conditions important to the magnitude of pollutant reductions
• Thick, tall and full coverage reduced pollution downwind of the road
• Gaps and porous vegetation led to no reductions or even higher concentrations

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Deshmukh, et al, 2019. Air Quality, Atmosphere & Health, 12(3)

Research Example

Review Articles

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Janhäll, 2015. Atmospheric Environment, 105, pp.130-137

Gallagher et al, 2015. Atmospheric Environment, 120, pp.61-70

Baldauf, 2017. Transport Res Part D: Transport & Environ, 52, pp.354-361

Abhijith et al, 2017. Atmospheric Environment, 162, pp.71-86

The U.S. EPA developed recommendations for planting and maintaining roadside vegetation

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Urban Vegetation Recommendations

• Used to design and implement planting projects in the U.S. and Europe
• Includes vegetation alone and combined with solid barriers
• Provides designs intended to:
• maximize the potential for air pollution and climate mitigation, and
• avoid unintended consequences and designs that may increase downwind concentrations and exposures

https://www.epa.gov/sites/production/files/2016-08/documents/recommendations_for_constructing_roadside_vegetation_barriers_to_improve_near-road_air_quality.pdf

Vegetative Barrier Recommendations

Areas desired for reduced pollutant concentrations should avoid gaps and edge effects

• Complete coverage from the ground to the top of the canopy
• Thickness adequate to reduce porosity and avoid gaps

Pine/coniferous trees and thick bushes/ hedges may be good choices

• Minimal or no seasonal effects
• Complex, rough, waxy surfaces

Mix of species (bushes/trees) may increase coverage and robustness

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Examples of full coverage, pine and hedge barriers

Pollutants can meander around edges or through gaps

• No spaces between or under trees
• No gaps from dead or dying plants; thus, maintenance is important

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Examples of inadequate barriers due to gaps and high porosity

Vegetative Barrier Recommendations

Combination of solid and vegetative barriers may have the most benefit for air pollution exposure mitigation

• Maximizes air pollutant dispersion from solid barrier with PM and BC removal by vegetation
• Provides initial air quality benefit while vegetation grows
• Use of climbing vegetation on solid surfaces to reduce PM and BC still uncertain

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Examples of solid/vegetation barriers

Combination Barrier Recommendations

Conceptual Applications

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Conceptual Applications

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Other Design Considerations

Vegetation characteristics:

• Species (e.g. native vs. non-native)
• Appropriateness for site
• Drought/flood resistant
• Road treatment tolerant (e.g. salt, sand)

Physical characteristics the barrier needs:

• Height, thickness, length and porosity
• Non-seasonal vegetation (conifers, bushes, etc.)
• Waxy leaf and branch surfaces for pollutant removal
• Low pollution/pollen emissions

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Urban vegetation, including roadside barriers, can have many additional benefits, including:

• Increased CO2 sequestration
• Methane removal in vegetation soils
• Improved urban cooling
• Reduced stormwater runoff/flooding
• Improved water quality
• Reduced noise levels
• Improved aesthetics/property values
• Enhanced community livability
• Improved general public health

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“Exposure to green space has been associated with better physical and mental health”

Urban Green Infrastructure Benefits

Dadvand et al. 2015, Proc. Nat Acad Sciences, 112(26)

Example Co-Benefit of Urban Green Infrastructure

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Example Co-Benefit of Urban Green Infrastructure

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Conclusions

• Climate and health concerns from transportation emissions have raised the importance of understanding how urban infrastructure can be used for air pollution mitigation
• When designed properly, urban and roadside green and built infrastructure can provide important air quality and SLCP reduction benefits

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For More Information:

Richard Baldauf, PhD, P.E.

U.S. Environmental Protection Agency

919-541-4386

Baldauf.Richard@epa.gov

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This presentation has been subjected to the Agency’s review process and has been approved for publication. These are the views of the authors and do not necessarily reflect official policy of the EPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.