Integrating Air Pollution and Climate Mitigation into Roadside Green Infrastructure Projects www.epa.gov/research a Richard Baldauf U.S. Environmental Protection Agency, Office of Research & Development, Washington, DC, USA U.S. Environmental Protection Agency, Office of Transportation & Air Quality, Ann Arbor, Ml, USA EPA-420-H-23-001 Abstract Climate Impacts from Transportation Roadside Vegetation Recommendations Air pollution is one of the leading causes of death and illness worldwide according to the World Health Organization. Exposures to air pollution for people who live, work, and go to school near large transportation sources has been shown to be of especially high risk due to the proximity and frequency of these exposures to vehicle emissions. While many roadside green infrastructure projects focus on stormwater management and other ecosystem services, recent research shows that roadside vegetation can also have a significant impact on local air quality as well. This research shows that certain roadside vegetation designs can greatly reduce local air pollution levels by 50% or more; however, other vegetation characteristics can have detrimental effects and deteriorate local air quality. Guidance is needed to support roadside vegetation plantings that do not adversely impact local air quality. In addition, this guidance can be used to promote roadside plantings that improves local air quality while also achieving other ecosystem services including mitigation of greenhouse gases, improved urban cooling, and improved stormwater management. Since many communities located near large transportation facilities are already overburdened by environmental impacts, improved roadside planting designs for air quality and climate benefits will support equitable, sustainable, and safer transportation systems while avoiding unintended consequences and public health concerns from urban green infrastructure projects in these neighborhoods. This poster will review the concerns related to air pollution exposures near transportation sources, previous research on the positive and negative air quality impacts created by roadside vegetation, and design characteristics and opportunities to provide air pollution and climate mitigation benefits. The poster will also review how integrating roadside vegetation with solid structures like noise barriers and fencing can further reduce local air pollution concentrations and avoid some of the potential negative impacts of roadside vegetation alone Air Pollution Impacts from Transportation Numerous health studies have shown that exposures to air pollutants emitted by transportation sources, especially when exposures to these emissions occur near the source of emissions such as highways and other large roadways, can be especially harmful to human health. A recent meta-analysis by the Health Effects Institute showed that people who live, work, and go to school within approximately 300-500 meters of large roadways face increased risks for numerous adverse health effects including asthma and other respiratory effects, cardiovascular illnesses, birth and developmental effects, and even premature mortality.2 Other studies have shown increased risks for additional adverse health effects including childhood leukemia, cognitive development, and neurological effects including autism. These studies generally show increased risks out to 500 meters from the road, air pollution measurement studies show that air pollution concentrations are especially high within the first 100-150 meters of the road.3 While this is a relatively short distance, the EPA estimates that over 50 million people live within just 100 meters of a major road and as many as 17,000 schools are located within 250 meters of a large roadway.4 Thus, mitigating these air pollution impacts on human health near the source are extremely important. U.S. Environmental Protection Agency Office of Research and Development Office of Transportation and Air Quality As of 2020, transportation sources emitted the highest amount of greenhouse gases (GHGs) for the fifth year in a row. The majority of these emissions occurred as carbon dioxide (C02) followed by methane (CH4) and nitrous oxide (N20). Not included in this inventory is the short-lived climate pollutant (SLCP) black carbon (BC), often referred to as soot. Transportation sources, especially diesel-powered vehicles, can emit significant amounts of BC. As noted by the United Nations, reducing ambient air concentrations of SLCPs, especially BC and CH4, will be critical in achieving the goal of limiting climate change to 1.5°C. CLIMATE MITIGATION PATHWAYS Avoided global warming by 2050 Air Pollution Emissions from Transportation Motor vehicles emit air pollution when operating through tailpipe emissions from gasoline and diesel fuel combustion, evaporation and leaking of fuel and fluids, wear from brake and tire use, rusting and deterioration of vehicle components, and the re-entrainment and suspension of dust and other materials deposited on the roadway. These emissions include PM2.5, PM10, and BC along with many other forms of airborne particles and gases. While strategies have been implemented to reduce vehicle emissions, notably the increased electrification of the motor vehicle fleet, this fleet transition will take decades to fully implement, and emissions will continue from brake and tire wear and the re-suspension of roadway materials. Thus, methods will continue to be needed to reduce air pollution exposures from traffic emissions, especially close to large highways and arterial roads. Roadside Vegetation Research Research has demonstrated that roadside vegetation can reduce air and climate pollutants when located adjacent to large roadways. Studies indicate that PM concentrations, including BC, can be reduced by as much as 50%, depending on the particle size and composition. PM concentration reductions are highest for larger, coarse PM10 as well as for very small particles below 100 nm in diameter (often called ultrafine particles). BC particles are typically in the ultrafine particle size range. Research also shows that concentrations of some gaseous pollutants can be reduced as well. Roadside vegetation reduces air pollution concentrations by two mechanisms: increasing the dispersion of pollutants after being emitted by nearby motor vehicles and deposition of particles and gases on vegetation leaf and branch surfaces. In order to effectively remove air and climate pollutants, the design and characteristics of the vegetation are extremely important. The result is lower roadway pollutant concentrations in the area protected by the vegetative barrier Pollutants are dispersed into the air by roadside trees Some pollutants are filtered and others are w *4 absorbed directly by foliage Air pollution produced by vehicles on heavily trafficked roadway Research shows the characteristics of the roadside vegetation are critical in determining whether traffic-emitted air pollution concentrations will be reduced, or if the presence of roadside vegetation will potentially cause increased air pollution concentrations in the near-road environment. In general, roadside vegetation must be tall, think, and have the leaves and branches completely cover from the ground to the top of the canopy to achieve pollutant reductions. If the vegetation has gaps and/or is highly porous, the vegetation can allow the air pollutants to pass through while also stagnating wind flow, leading to an increase in downwind air pollution concentrations. The U.S. EPA developed recommendations to highlight the characteristics needed by roadside vegetation to improve local air quality.7 This report also summarizes other important considerations to achieving air quality benefits from roadside vegetation including species types, site characteristics, and maintenance. The report also describes methods to combine vegetation with solid barriers such as noise walls and fencing to achieve air quality benefits, which research shows can be more effective than vegetation alone. Roadside vegetation designs and characteristics that can result in decreased downwind air pollution concentrations. Roadside vegetation designs and characteristics that can result in increased downwind air pollution concentrations. Combining solid barriers with trees and hedges can result in the highest reductions of downwind air pollution concentrations compared with either solid barrier or vegetation alone. Open Road: Single o. low mul.i-story buildings along a busy road L ' 'U ~ v_ ] Open Road: A busy freeway alongside houses Conceptual examples show the application of planting roadside vegetation along the highway right-of- way in residential areas and within street canyons. Disclaimer, Acknowledgements, References 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. The author would like to acknowledge the contributions of Sheila Batka and Ken Davidson of the U.S. EPA who lead the implementation of pilot studies in Detroit and Oakland, respectively, and Olivia Ryder of Sonoma Technology who contributed to many of the graphics used in this presentation. The author also acknowledges many other collaborators on the research efforts that informed this summary. 1 World Health Organization (https://www.who.int/health-topics/air-pollution) 2 Health Effects Institute (https://www.healtheffects.org/publication/svstematic-review-and-meta-analvsis-selected-health-effects-long-term-exposure-traffic) 3 Karner et al. 2010, Environ Science & Tech, 44(14), pp.5334-5344 4 U.S. EPA Best Practices for Reducing Near-Road Pollution Exposure at Schools (https://www.epa.gov/mobile-source-pollution/how-mobile-source-pollution- affects-vour-health#best-practices-for-schools) 5 Baldauf, 2017. Transport Res Part D: Transport & Environ, 52, pp.354-361 6 Abhijith et al, 2017. Atmospheric Environment, 162, pp.71-86 7 U.S. EPA Recommendations for Constructing Roadside Vegetation Barriers to Improve Near-Road Air Quality (https://www.epa.gov/air- research/recommendations-constructing-roadside-veeetation-barriers-imorove-near-road-air) The World Health Organization (WHO) reports that air pollution is a leading cause of death and illness worldwide. 1 Exposures to particles in the air are especially damaging to human health and welfare. These airborne particles are very small and are categorized as PM10 (particles less than 10 pm in diameter) and PM2.5 (particles less than 2.5 pm in diameter). These particles are smaller than a human hair as shown in the figure below. ------- |