Vegetated stormwater practices (green roofs, tree trenches, bio-retention, stormwater ponds/wetlands, and swales) can be designed, constructed and maintained to reduce emissions of air pollutants and intercept particulate matter to help improve air quality. Plants can filter out particulate matter and air borne pollutants via uptake and absorption into plant tissue. A variety of airborne contaminants can be removed by vegetated stormwater practices including CO2 (carbon dioxide), O3 (ozone), SO2 (sulfur dioxide), and PM10 (particulate matter) among other airborne particles and contaminants. Green roofs can also help regulate air temperature by reducing the heat island effect.
A study performed in Chicago, Illinois demonstrated that several air pollutants (Ozone, Nitrogen Oxide, Particulate Matter, and Sulfur Dioxide) were removed through the installation of Green Roofs on rooftops. The highest level of air pollution removal occurred in May and the lowest in February1.
A second study in Toronto, Canada used the Urban Forest Effects (UFORE) model developed by the USDA Forest Service Northeastern Regional Station and quantified pollution removal for contaminants such as NO2, SO2, CO2, PM10, and O3. Different vegetation scenarios were developed within the Toronto study to compare the vegetation variety on their effect on air contaminants2. Results found that grass on roofs could supplement the effect of trees/shrubs in air pollution mitigation, and that by placing shrubs on roofs there would be a more sizable impact.
Studies have also shown that green roofs can reduce diesel engine air pollution and that a significant reduction of SO2 (37%) and nitrous acid (21%) directly above a newly installed green roof. Some studies suggest the removal of dust particles on the order of 0.2 kg of particles per year per square meter of grass roof3.
Similar to green roofs, Tree trenches and tree box BMPs improve air quality by absorbing air pollutants and intercepting particulate matter. Trees help reduce the heat island effect and reduce energy consumption, which improves air quality and reduces the amount of greenhouse gases present in the atmosphere.
Bio-retention BMPs (rain gardens, bioswales, wetlands, etc.) can improve air quality by through uptake of criteria air pollutants and the deposition or particulate matter which could otherwise migrate into the atmosphere.