Car parks that see less intensive use can be can be paved with surfacing open to vegetation and be planted with trees. These car parks can serve as cool islands in the town or city. A study performed by research institute TNO Duyzer et al., 2011 reveals that industrial estates, harbours and business estates are some of the hottest urban areas. Planting trees on semi-paved car parks would be one way to lower temperatures. An additional benefit is that the cars underneath a tree canopy will also stay cooler inside and that the trees will purify from the air some of the emissions generated by the cars.