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.
Since the early 1970s, research to evaluate ozone levels in ambient air has been in progress at several rural and urban site in New York State. The sites were chosen to provide ozone data above and below the nocturnal inversion layer.
Ozone from upwind sources has been shown to significantly affect both the urban and remote rural areas. Concentration isopleths show that ozone created in the urban plume of the larger urban areas significantly affects areas downwind under the plume.
The sources of ozone in the remote rural areas are still not clear. Principal ozone sources are stratospheric ozone, photochemical production from terpenes and hydrocarbons emitted from local vegetation, and ozone transported via urban plumes. Each of these three sources can be a significant contributor.
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