Other sources of ozone include power plants, buildings, and lawn mowers. Trees are critical components of our environmental life support system and are necessary to prevent or minimize the negative combination of high temperature and vehicle exhausts from spinning out of control and causing harmful ozone levels. Trees improve air quality by providing a cooling effect through transpirational water loss from their leaves and by filtering atmospheric pollutants through their leaves. By decreasing both the temperature and the amount of pollutants in the atmosphere, trees can have a positive effect on air quality. This is significant since federal highway funds can be withheld from Atlanta and other metropolitan areas because of poor air quality.
Ozone is a major contributor to poor air quality in urban areas.
Perhaps an appropriate analogy would be the filter for a home air conditioning unit. If you remove the filter for the air conditioning unit, the cooling unit will become clogged with trash and will stop functioning. Ionic materials comprise the major exhaust pollutants of vehicles. Trees were able to remove large quantities of each type of material. Increased Water Run-Off.