The Greenest Air Filters: Impact of Urban Green Spaces on Air Quality

Urban green spaces have been recognized as a practical strategy to improve urban air quality and reduce health risks associated with air pollution and extreme heat. In cities, exposure to elevated air pollutant concentrations (e.g., ozone and particulate matter) contributes to respiratory and cardiovascular illness, while higher temperatures linked to the urban heat island effect can intensify heat-related medical events. This paper reviews literature on urban green spaces and their ability to improve air quality through three pathways: (1) lowering air temperature through shade and evapotranspiration, (2) filtering and removing air pollutants, and (3) supporting greenhouse gas mitigation through carbon storage and sequestration. The paper uses a targeted evidence scan to establish key outcome categories and then presents a structured comparison of two exemplar case studies. Two exemplary case studies illustrate these pathways by examining how vegetation relates to urban heat patterns and heat-related health outcomes, and by estimating how urban trees remove air pollutants and the associated economic value. Together, these studies demonstrate that urban vegetation can produce measurable environmental and public health benefits through both cooling effects and pollutant removal. However, green spaces alone are unlikely to fully offset major sources of air pollution and greenhouse gas emissions without broader changes in land use, energy systems, and environmental practices.