The Tree BVOC Index
Urban trees can produce a number of benefits, among them improved air quality. However, biogenic volatile organic compounds (BVOCs) emitted by some species are ozone precursors. Modifying future tree planting to favor lower-emitting species can reduce these emissions and aid air management districts in meeting federally mandated emissions reductions for these compounds. Changes in BVOC emissions result from transitioning to a lower-emitting species mix in future planting. A simplified method for calculating the emissions reduction and a Tree BVOC index (TBI) based on the calculated reduction has been developed. It is a prescriptive approach that provides an estimate of projected and actual emission reductions, gives users a clearly defined target to reach and a method to continuously monitor progress, is completely transparent to users and regulators, and eliminates labeling of tree species, thereby facilitating verification and enforcement in a regulatory environment. Calculations are readily implemented in a spreadsheet application using numbers of each species planted over the life of the project, the number of years in the project, and tabulated daily emissions values, which account for differences due to species, size, and local climate.