Biogenic hydrocarbon emissions: a consideration for large-scale tree planting programs

Although principal gas exchange of green plants includes water vapor, carbon dioxide and oxygen, hundreds of additional carbon-containing compounds are also emitted by plants. These volatile organic compounds (VOC) react with oxides of nitrogen (NOx) to form ozone, a secondary pollutant in the lower atmosphere, as well as secondary organic aerosols. Emission strength of specific biogenic VOC (BVOC) is dependent upon species-specific emission rate and amount of leaf mass, as well as environmental factors such as light and temperature. Understanding the BVOC contribution of plants in a polluted region is critical for formulating effective air quality attainment policy, since reductions in photochemical products depend on reductions of precursor VOC, NOx, or both. Also, biogenic compounds may have reaction rates greater than those of anthropogenic compounds such as those found in gasoline. Large-scale tree planting programs can affect BVOC emissions in an airshed depending on the mix of species planted. Species selection for urban tree planting programs should consider BVOC emission rate in addition to other horticultural characteristics, and databases exist for BVOC emission rates as do approaches for estimation of BVOC emission rates for unmeasured species.