Abstract
Continuous analyses of peroxyacetyl nitrate (PAN) were performed at a forest site in the Eggegebirge, F.R.G., where severe forest decline has occurred in the last decade. An automatically working analysis system was installed inside a spruce stand. Air samples from three elevations (1 m, 7.5 m and 12.5 m above ground) were simultaneously analyzed. The results obtained show that PAN-concentrations in the range below 0.2 ppb prevailed. Several episodes with elevated PAN concentrations, up to 4.6 ppb, were measured. High PAN-levels were more abundant in spring and summer than in winter. PAN concentrations above the canopy were usually higher than within the canopy. Near ground level the lowest concentrations were found. This concentration profile and the detailed discussion of episodes with elevated PAN concentrations, in conjunction with additional meteorological data, showed that PAN formation within or above the forest canopy is relatively low compared to the input by long-range transport. Thus it was concluded that biogenic hydrocarbons emitted by the forest trees do not significantly contribute to the formation of observed PAN peak concentrations. The measured concentrations did not indicate a phytotoxic burden by PAN and PAN homologous photooxidants at this site.
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