A potential environmental function for vegetation, in general, and trees, in particular, is the reduction of air pollution, especially in neighborhoods alongside roadways. Ultrafine particles (UFP), the smallest component of particulate matter, is produced by many processes including the burning of diesel and gasoline fuels and is associated with cardiovascular effects and pulmonary diseases such as atherosclerosis, asthma, fibrosis and cancer. Recent in vitro studies have found associations between UFP and elevations in pro- inflammatory cytokines and both reactive oxygen and nitrogen species leading to oxidative stress in human bronchial epithelial cells. Pollution reduction strategies can be complex and expensive, which encourages researchers to explore more affordable and locally designed options for municipalities, school districts and neighborhoods that may be disproportionately exposed. The overarching goal of this project is to determine if and under what conditions trees can function to mitigate UFP air pollution and define any difference in cardiorespiratory effects based on cellular response to exposure. Studies have documented that a stand of trees next to a roadway, a tree barrier, can reduce near- roadway UFP and black carbon ([BC] solid soot particles); however research remains limited. Tree barriers associated with the greatest reductions have been composed of evergreens with branches that extend to the ground and are sufficiently dense to serve as a filter. Combined tree and noise barriers have also been shown to reduce UFP concentrations in some studies. We are not aware of any studies, to date, that have evaluated the impact of UFP collected in the presence of a tree barrier on cellular function. We have developed a novel assessment, based on experiments in nanotechnology, to measure oxidative stress and inflammation in human epithelial cells when exposed to UFP. This study will test the hypothesis that a roadway tree barrier or a tree/noise barrier will reduce near- roadway UFP concentration, alter composition and lead to decreased reactivity in human epithelial cells. Multiple sites in the Atlanta metropolitan area will be selected, each alongside a tree barrier, a tree/noise barrier or no barrier. UFP number, UFP mass and BC concentrations will be measured on road and on site at each location on non-consecutive days. Primary small airway epithelial cells will be exposed to the particles in order to evaluate differences in 1) epithelial cell injury; 2) inflammatory response; and 3) phenotypic alterations including epithelial mesenchymal transitions, which has been linked to environmental asthma. Over 96 million people live within three blocks (approximately 300 m) of a major roadway. Since trees often exist near roadways across the country, our study can substantially impact public policy, exposure assessment and epidemiological studies. We will also document potential mechanisms of effect between UFP and cardiorespiratory effects and explore how they differ based on composition.
Our overarching goal is to determine if and under what conditions trees or combination tree/noise barriers can function to mitigate near-roadway particulate matter air pollution and to define any difference in cardiorespiratory health effects based on exposure. We will test the hypothesis that roadway tree barriers and combination tree/sound barriers will reduce near-roadway particulate matter concentration, alter its composition and lead to decreased reactivity in exposed human epithelial cells. A significant proportion of the U.S. population lives near busy roads and our study can substantially impact public policy, exposure assessment and epidemiological studies.
