Urban trees and air amelioration capability

Urbanisation processes have increased pollution levels in urban areas, and vehicular traffic is one of the major sources of air pollution. Understanding the urban ecosystem pollution dynamics require long-term researches because the many factors involved (i.e. climate, pollution sources, urban characteristics, trees presence, traffic density, vehicle type). In the last years investigators are themselves concentrating on the possibility to develop models that can quantify the role of urban trees in removing pollutants from atmosphere; nevertheless, these models need many data on the species composition, age, structure, health, and geographic distribution. We analysed the main factors affecting atmospheric CO2 and heavy metal concentrations in Rome in the long term, and the trees air amelioration capability, considering the most important deciduous and evergreen species widely distributed in the city. These species have a different role in carbon dioxide sequestration and in bioaccumulation of heavy metals. Moreover, trees contribute to air temperature mitigation by shading and transpiration, thus lowering energy consumption for air conditioning during summer. Incorrect pruning practices can reduce or undo the trees air amelioration role. Such a role depends on many factors, including trees species, plant size and leaf longevity. In particular, information on air pollution could be deduced from heavy metal concentration in plant tissues, offering a low-cost information about urban environment quality. Moreover, crown volume is a discriminant factor for carbon sequestration, and leaf longevity is the most important leaf trait changing in response to heavy metal pollution. It is important to identify the tree species mostly contributing to air amelioration, and the most discriminant plant traits helping long-time monitoring and city management. The results might be exported into other urban areas to improve air quality enhancing social benefits.