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

Abstract

Traffic-related air pollution is a persistent concern especially in urban areas where populations live in close proximity to roadways. Innovative solutions are needed to minimize human exposure and the installation of vegetative barriers shows potential as a method to reduce near-road concentrations. This study investigates the impact of an existing stand of deciduous and evergreen trees on near-road total particle number (PNC) and black carbon (BC) concentrations across three seasons. Measurements were taken during spring, fall and winter on the campus of a middle school in the Atlanta (GA, USA) area at distances of 10 m and 50 m from a major interstate highway. We identified consistent decreases in BC concentrations, but not for PNC, with increased distance from the highway. In multivariable models, hour of day, downwind conditions, distance to highway, temperature and relative humidity significantly predicted pollutant concentrations. The magnitude of effect of these variables differed by season, however, we were not able to show a definitive impact of the vegetative barrier on near-road concentrations. More detailed studies are necessary to further examine the specific configurations and scenarios that may produce pollutant and exposure reductions.

Urban Vegetation in Air Quality Management: A Review and Policy Framework

“…Forests near major roads may slightly worsen air quality in terms of traffic-related NO 2 pollution, however for PM 2.5 pollution, no difference between open and vegetated areas was found and for coarse PM (>PM 2.5 ) and large PM (>PM 10 ), the air pollution concentration levels were lower in the forest than in open transects [19]. Finally, in one study, a significant decrease according to the distance from the traffic lane was observed for PM 10 ,PM 2.5 ,and black carbon (BC) concentrations [24], while in another study, it was concluded that only a decrease in BC concentrations occurred with increased distance from the road and a similar effect was not observed for PM pollution [23].…”

“…On-site air quality measurements, also if coupled with field vegetation inventories, and data analysis [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] On-site air quality measurements or soil sampling, measurements of pollution removal by means of laboratory techniques, including instrumental analysis on plant samples (e.g., microscopic analysis, spectroscopy, gravimetry, gas exchange measurements, wind tunnel experiments on leaves or branches etc.) and data analysis [31][32][33][34][35] Measurements of pollution removal by means of laboratory techniques, including instrumental analysis on plant samples and data analysis [11][12][13] Estimates of pollution removal by vegetation or statistical analysis based on field plant inventories or remote sensing data and existing literature/databases or air quality data [60][61][62][63][64][65][66] Modelling Approaches…”

“…At the micro-scale level, single elements of the geometry of the urban canopy layer were investigated, such as buildings or building complexes, street canyons, roads, or urban parks. In particular, vegetation around building complexes [15], near-road locations [14,19,21,23,24,[26][27][28]34,75,76], urban green spaces [16,22,44,63], or green roofs [17,29] were considered. The studies at the neighbourhood scale, in which several urban blocks or large open urban areas were considered, or at the city scale, which included the area of the entire municipality, were less common.…”

“…Plant level study [10][11][12][13][31][32][33][35][36][37][38][39][40][41][42][43][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]65,69,73] Local scale [14][15][16][17]19,[21][22][23][24][26][27][28][29]34,44,63,75,76] Neighbourhood scale [18,…”

“…For local-scale studies, to date, the varying methodologies and habitats do not allow for meaningful comparisons [19]. Similarly to plant-scale studies, a variety of local conditions, such as meteorological factors, may have a significant impact on the results [23,24]. Although increasing the amount of urban greenery was found to be adversely associated with local air pollution concentration levels in various scenarios and it has been advocated as a mitigation strategy (e.g., [15,26,29,34]), other studies were less optimistic.…”