Do Urban Forests Enhance Air Quality?

Abstract

There is a need for scientific understanding of how urban landscapes affect human environments regarding air, water and soil quality. This article is a review of the current science behind how urban trees influence the level of ambient air pollutants that exist in common urban airsheds. The paucity of data and directed science in this area is notable with unresolved controversy surrounding the variables used to determine the amount of air pollutants, such as particulate matter, ozone, and nitrogen and sulphur oxides, that trees can remove or add to the atmosphere. Use of percentage tree coverage, percentage urban landscape coverage, leaf area index, pollutant deposition velocity, and ambient air concentration data for New Zealand's largest city, Auckland (population 1.2 million, Statistics New Zealand 2001) provided an estimate of an annual loss of 1230 tonnes of nitrogen dioxide, 1990 tonnes of ozone and 1320 tonnes of particulate matter due to existing Auckland woodlands.