title: Field investigation of roadside vegetative and structural barrier impact on near-road ultrafine particle concentrations under a variety of wind conditions.
abstract: Roadside barriers, such as tree stands or noise barriers, are prevalent in many populated areas and have been shown to affect the dispersion of traffic emissions. If roadside noise barriers or tree stands are found to consistently lower ground-level air pollution concentrations in the near-road environment, this may be a practical strategy for reducing exposures to air contaminants along populated traffic corridors. This study measured ultrafine particle (UFP) concentrations using an instrumented mobile measurement approach, collecting data on major roadways and in near-road locations for more than forty sampling sessions at three locations in central North Carolina, USA. Two of the sampling sites had relatively thin tree stands, one evergreen and one deciduous, along a portion of the roadway. The third sampling site had a brick noise wall along a portion of the road. At 10 m from the road, UFPs measured using a mobile sampling platform were lower by approximately 50% behind the brick noise wall relative to a nearby location without a barrier for multiple meteorological conditions. The UFP trends at the vegetative barrier sites were variable and the barrier effect is uncertain. In some cases, higher concentrations were observed behind the vegetative barrier, with respect to the clearing, which may be due to gaps in the thin tree stands allowing the transport of traffic-related air pollution to near-road areas behind the vegetation. On-road sampling revealed no consistent difference in UFP levels in on-road portions of the road with or without a roadside barrier present. These findings support the notion that solid roadside barriers may mitigate near-road impact. Given the co-benefits of vegetative barriers in the urban landscape, research regarding the mitigation potential of vegetative barriers of other configurations (e.g., greater density, wider buffer) is encouraged.
authors.affiliation: US EPA, Office of Research and Development, National Risk Management Research Laboratory, Research Triangle Park, NC, USA. hagler.gayle@epa.gov
authors.forename: Gayle S W
authors.initials: GS
authors.lastname: Hagler
authors.forename: Ming-Yeng
authors.initials: MY
authors.lastname: Lin
authors.forename: Andrey
authors.initials: A
authors.lastname: Khlystov
authors.forename: Richard W
authors.initials: RW
authors.lastname: Baldauf
authors.forename: Vlad
authors.initials: V
authors.lastname: Isakov
authors.forename: James
authors.initials: J
authors.lastname: Faircloth
authors.forename: Laura E
authors.initials: LE
authors.lastname: Jackson
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution; D004784:Environmental Monitoring / Q000295:instrumentation; D052918:Environmental Restoration and Remediation; D009657:North Carolina; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D013997:Time Factors; D014197:Trees; D001335:Vehicle Emissions / Q000032:analysis*; D014919:Wind
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D001335:Vehicle Emissions