by DJ Nowak, DE Crane, JC Stevens
Urban Forestry & Urban Greening 4:115-1232006
The ability of urban trees and shrubs to improve air quality (in terms of O3, PM10, NO2, SO2, and CO) was modeled for 55 continental U.S. cities and all urban areas of the U.S. combined. Local hourly air pollutant concentrations and meteorological data were incorporated into the model together with tree canopy cover determined from aerial imagery sampling or radiometer data and estimates of leaf-on and leaf-off times. The greatest total air pollutant removal occurred in Jacksonville, FL, and the greatest air pollutant removal per unit of canopy cover occurred in Los Angeles, CA. Factors influencing pollution removal include tree canopy cover, pollution concentration, duration of the in-leaf period, amount of precipitation, and other weather factors. Total air pollutant removal (all five pollutants) by urban trees and shrubs in the U.S. was estimated at 711,000 t per year, which is less than 1% of the total air pollutant load. The estimates are likely conservative as they do not account for the ability of the tree canopy to stop upper-atmosphere pollutants from reaching ground level.