Volatile Organic Compound Emissions From Citrus In California Airsheds

Volatile organic compounds (VOC) are emitted from both biogenic and anthropogenic sources, and in the lower atmosphere may participate in photochemical reactions with oxides of nitrogen (NOx) to produce ozone, particulate matter, and other secondary air pollutants.  Green plants are sources of biogenic VOC, with emission strength dependent upon species-specific emission rate and amount of leaf mass, as well as environmental factors such as light and temperature.  Understanding the biogenic VOC contribution in a region is critical for formulating effective air quality attainment policy, since reductions in photochemical products depend on reductions of precursor VOC, NOx, or both.  A study to measure VOC emissions from five Citrus species and varieties was conducted using a dynamic enclosure technique, followed by a field study focusing on orange ‘Parent Navel’ using an eddy covariance technique.  Emission rates per g dry leaf mass were low compared to previously identified high-emitters such as certain native oak species and eucalyptus.  Also, the principal VOC emitted by citrus were the oxygenated VOC methanol and acetone, but isoprene and its oxidation products were found at low levels.  These results indicate the citrus species studied have an emission profile unlike those of high-emitters and also unlike native pines and oaks surrounding California’s Central Valley.  Despite the extensive land area of citrus cultivation in California, these results imply low BVOC contribution from citrus to regional air masses.