URBAN TREES AND AIR POLLUTION

In urban areas, an evolution of the nature of air pollution has been noticed, and if until the eighties the major sources were domestic heating and industry with large emissions of SO₂, now the main source is to be found in the exhausts from motor vehicles, with emissions of NOx, CO₂, hydrocarbons and dust.
On sunny days in summer, these substances contribute to the formation of ozone, a more phytotoxic pollutant, with the highest concentrations in urban surroundings.

In many towns from West-Europe countries, the air concentration of these new pollutants is more often under the threshold of phytotoxicity, and very sensitive plants, as the lichens, can again be observed downtown.

If the vitality of urban trees is always a problem in spite of the decreasing impact of air pollutants, it comes mainly from their soil environment : water stress, asphyxia, etc… During cold periods, the use of salt for snow or ice removal enhances their soil problems.
Planting trees can reduce local temperature and consequently reduce the amount of ozone in atmosphere.
But planting high hydrocarbon-emitting trees, particularly in southern cities, can conversely increase ozone formation.

Generally urban trees can not significantly reduce air pollution by intercepting particulate and/or absorbing gaseous pollutants through their leaves, but they may be used as good bio-indicators and bio-accumulators of air pollutant effects for detection, recognition and monitoring purposes.

International Symposium on Urban Tree Health

J. Garrec

Urban trees, air pollution

https://doi.org/10.17660/ActaHortic.1999.496.38