LOW-EMITTING URBAN FORESTS - A TAXONOMIC METHODOLOGY FOR ASSIGNING ISOPRENE AND MONOTERPENE EMISSION RATES

Large-scale tree planting programs have been proposed, and are being i mplemented, as a means of reducing energy demand, mitigating urban hea t islands, and improving air quality. However, many species of trees e mit highly photochemically reactive hydrocarbons and the rates of such emissions can vary by four orders of magnitude, depending upon the tr ee species. Thug, planting of high-emitting trees species on a massive scale has the potential to adversely affect air quality rather than l eading to improvement. However, the selection of low-emitting trees is difficult because emission rates have been experimentally determined for only a limited number of species. The present study describes a me thodology for assigning biogenic emission rates based on taxonomic rel ationships. Using this methodology, direct emission measurements from 124 tree and shrub species found in the California South Coast Air Bas in (SoCAB) are used to assign emission rates to 253 other species foun d in the SoCAB but for which there are no measured emission rates. The combined listing of 377 species is ranked according to total (isopren e and monoterpenes) biogenic emission rate on an hourly basis. Althoug h the ranking of trees developed here is specific to Southern Californ ia, the methodology described can be applied to other geographic areas to assist in the planting of low-emitting urban forests.