Barriers by Roadways: The Efficacy of Long Beach’s Great Wall of Mulch in Reducing Pollutant Concentrations in Adjacent Areas

Research Lead: Suzanne Paulson

UC Campus(es): UCLA

Problem Statement: Air pollution near highways is a public health concern, especially in densely populated urban areas. Roadside barriers are a mitigation strategy commonly used to reduce the exposure of nearby communities to air pollution. In 2013, the City of Long Beach installed a novel type of barrier, called the “Great Wall of Mulch,” constructed using mulch contained within a chain link fence enclosure. The barrier separates a park from a highway with large volumes of truck traffic, and it was touted by city officials as mitigation for nearby freight and industrial activity.

Project Description: Researchers at UCLA conducted measurements of ultrafine particles surrounding the Great Wall of Mulch using hand-held instruments and instruments installed in an electric vehicle. The research team conducted measurements during afternoons when the wind was roughly perpendicular to the freeway, when the park was most impacted by nearby pollution sources. The research found that air quality at Hudson Park is consistent with a moderate amount of pollution reduction behind the Great Wall of Mulch. Part of the observed reduction, however, may be due to tall trees planted in the park near the barrier. In addition, the project found that there is still room for improvement. A very effective barrier would usually result in even less air pollution than that observed at Hudson Park.

Status: Completed

Budget: $27,500

Project Partner(s): California Air Resources Board, Caltrans Maintenance and the City of Long Beach

Policy Brief(s):
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