Determination of the biogenic emission rates of species contributing to VOC in the San Joaquin Valley OF California

Abstract

As part of an extensive effort to characterize biogenic hydrocarbon emission rates in the San Joaquin Valley and surrounding areas during the SJVAQS/AUSPEX field experimental period, July-August 1990, measurements were made for the first time of isoprene, terpene, and other VOC emission rates from blue oak (Quercus douglasii), foothill pine (Pinus sabiniana), and a ground cover plant called tarweed (Holocarpha sp.) at a rural site near Mariposa, CA. A flow-through plant enclosure method was used to measure the emission flux rates from these species; the plant limb or whole plant was flushed with clean air just prior to hydrocarbon sampling. Samples of the plant emissions were collected on Tenax GC or Tenax GC-Carbosieve S-I1 cartridges and analysed by gas chromatography- Fourier transform infrared-mass spectrometry (GC-FTIR-MS). Quantifiable biogenic emissions from two blue oak specimens consisted only of isoprene, with an average emission rate of 8.4 μg g-1 dry biomass h-1. Emission rates (above the detection of about 0.05 μg-1 h-1) from two foothill pine specimens consisted mostly of α-pinene; an average emission rate of 0.64 μg-1 h-1 of α-pinene was observed. The tarweed species emitted both α- and β-pinenes, along with other terpene and oxygenated species, some of which have been tentatively identified. The emission rates of biogenic hydrocarbons from foothill pine and blue oak species as determined in this study make these species potentially significant contributors to summertime VOC levels in the San Joaquin Valley of California, based on vegetation classification data and the predominant summer meteorology. © 1994.