ORGANIC-CHEMICALS IN THE AIR AT WHITAKER FOREST SIERRA-NEVADA MOUNTAINS, CALIFORNIA

Air samples from a rural forested site in the Sierra Nevada Mountains were analyzed for volatile organic compounds by a thermodesorption GC/MS technique. Approximately 120 compounds were characterized by their mass spectra, with identification achieved for about 70 of these substances. A high proportion of biogenically emitted substances was found and the concentration of anthropogenic chemicals was relatively low. Twenty-one terpenoid compounds (C10H16 and oxygenated derivatives) and p-cymene were identified, and a single sesquiterpene, tentatively identified as longifolene, was also found. Nopinone (bicyclo[3.1.1]-heptan-2-one, 6,6-dimethyl-) and alpha-pinene oxide (3-oxatricyclo-[4.1.1.02,4]-octane, 2,7,7-trimethyl), both possible pinene degradation products, were among the compounds detected, although it is possible that the observed levels of one or both of these included contributions from formation during the sampling. The strong influence of local vegetative emissions on the composition of the forest air was confirmed by quantitative analysis. Concentrations of single monoterpenes up to 6.8-mu-g m-3 were found, whereas toluene was in the range of 0.3-mu-g m-3. The results from the forest site are compared with urban air samples collected in Riverside, California.