Air pollution mitigation by urban greening

Air pollution in urban areas is a serious threat to human health. Urban greening may improve air quality by intercepting air pollutants on leaf surface. In the present review the effects of air pollutants on human health were analyzed. In addition, the characteristics of vegetation which can optimize air pollutants interception by plants were reported. The analysis of the literature shows how the planting scheme details (density of vegetation, disposition of plants, global dimensions of the green infrastructure) are the main factors influencing the impact of plants on air quality. The same planting scheme may have opposite effects depending on the planting site characteristics. Vegetation barriers composed by continuous, dense and tall vegetation were found to be particularly effective in intercepting and reducing air pollutants deriving from traffic in open areas. Differently in street canyons, a too dense vegetation can hinder air circulation thus increasing air pollution concentration. Finally, in the last part of the review some guidelines with the principal favorable characteristics of vegetation for improving air quality are reported.