Science Inventory

Phenology of a Vegetation Barrier and Resulting Impacts on Near-Highway Particle Number and Black Carbon Concentrations on a School Campus

Citation:

Hemphill-Fuller, C., D. Carter, M. Hayat, R. Baldauf, AND R. Hull. Phenology of a Vegetation Barrier and Resulting Impacts on Near-Highway Particle Number and Black Carbon Concentrations on a School Campus. International Journal of Environmental Research and Public Health. Molecular Diversity Preservation International, Basel, Switzerland, 14(2):160, (2017).

Impact/Purpose:

Summary of a Georgia State/Georgia Tech project on near-road air pollution and school impacts

Description:

Air quality is a pressing issue in the urban environment contributing significantly to the global burden of disease [1]. Traffic-related air pollution (TRAP) is a mix of chemicals produced from the burning of diesel and gasoline in vehicles including particulate matter (PM), oxides of nitrogen, carbon monoxide, polycyclic aromatic hydrocarbons (PAHs) and metals as well as particulate emissions from brake and tire wear. TRAP has been associated with adverse health outcomes including asthma, lung cancer, cardiovascular disease and mortality [2]. A 2010 assessment by the Health Effects Institute that evaluated many epidemiological studies concluded that there was “sufficient” evidence for long-term exposure to TRAP and asthma exacerbation in children and borderline “sufficient” evidence for asthma onset in children. The report concluded “suggestive, but not sufficient” evidence for exposure and all-cause mortality, cardiovascular morbidity and decrements in lung function for both children and adults [2]. Variation in TRAP is driven by road layout, traffic volume and fleet mix on roads and highways [3]. Unlike regional air pollutants there is greater intra-urban variation than inter-urban variation in ambient concentrations of TRAP. Some components exhibit steep gradients near roads particularly carbon monoxide, nitric oxide, nitrogen dioxide, and particles in the ultrafine ([UFP] diameter <0.1 µm) and coarse (diameter 2.5 – 10 µm) ranges [3, 4]. Near road concentrations are related not only to roadway proximity, but also local meteorology including wind direction, wind speed and precipitation [3]. Higher concentrations are typically found downwind of roadways. High winds increase turbulence and dispersion and tend to decrease associations, while very calm or no wind may increase local concentrations. Health effects have been most closely linked to the particulate matter component of TRAP including respiratory conditions, cardiovascular disease and lung cancer [5]. Field studies identify the highest concentrations of TRAP to be for those traveling in traffic and living close to major roads and highways [3, 6-8]. Multiple methods have been proposed and implemented to reduce air pollutant concentrations and population exposures to air pollutants on and near large roads and highways including motor vehicle tailpipe emission standards, increased transit to reduce vehicle activity, limiting time spent near large roads and physical barriers [9, 10]. Given the cost and complexity of these strategies, municipalities and communities may be interested in identifying other possibilities to reduce the impact of local sources of air pollution. One possibility gaining more interest is the use of vegetation to reduce concentrations of TRAP at both the macro-level (across an entire city) and micro-level (from local roadways) [11-15]. In general, TRAP concentrations are higher in urban areas; which usually corresponds to lower vegetative cover although there is significant variation in vegetative cover between cities [12]. Nowak et al created a model comparing the number of trees, tree density, tree cover, leaf area index, and most common tree species for 14 U.S. cities [16]. The lowest model estimates were recorded in Casper, WY for tree density (9.1 trees/ac), tree cover (8.9%), and leaf area index (LAI) (0.3), and the highest measurements in Atlanta, GA for tree density (111.6 trees/ac), tree cover (36.7%), and LAI (2.2). Increased PM2.5 removal and air quality improvements were related to greater tree density, cover, and LAI and the total amount of PM2.5 removal annually by trees varied from 4.7 tonnes in Syracuse, NY to 64.5 tonnes in Atlanta, GA [13]. Removal of up to 0.36 g m-2 yr-1 was estimated for Atlanta, GA [13]. Average annual percent air quality improvement ranged between 0.05% in San Francisco, CA to 0.24% in Atlanta, GA