The total terpene concentration beneath the canopy of an eastern United States coniferous forest was found to be of the order of 50 μg/m3. Similar measurements within the forest but outside the canopy ranged from 3 to 32 μg/m3. Two samples collected at a mountain summit above the tree line were found to contain 7 and 27 μg/m3 total terpenes. Downwind from the coniferous forest in an area of deciduous vegetation the mean morning total terpene level was 4 μg/m3 and increased to 11 μg/m3 during the afternoon. Unidentified species, primarily in the C5–C9 range, were observed in total concentrations which averaged approximately twice the sample total terpene value. Results indicate a concentration range of 8–130 μg/m3 for C5–C10 organics in rural atmospheres in the Adirondack Mountain region of New York State. It is concluded that the majority of observed organics are of natural origin.
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