Estimating the ozone-forming potential of urban trees and shrubs

A method is presented for estimating the ozone-forming potential of biogenic hydrocarbon emissions from trees and shrubs, using the California South Coast Air Basin (SoCAB) as a case study. Hourly isoprene and monoterpenes emission rates for 308 tree and shrub species found in the SoCAB were combined with diurnal temperature and light intensity data for a representative summer day in the SoCAB to develop daily emission rates. These daily emission rates for each species were then normalized to a per tree basis using vegetation class biomass factors derived from reported leaf mass constants and tree canopy volumes. The ozone-forming potential for each of the tree and shrub species was estimated by combining the daily per tree emission rates with published maximum incremental reactivities (MIRs) for isoprene and monoterpenes. The resulting ranking of trees by ozone-forming potential can be used in tree species selection for future large-scale tree planting programs, and provides a more appropriate basis for selection than using only mass emissions of biogenic hydrocarbons.