High concentrations of reactive biogenic VOCs at a high altitude site in late autumn

Volatile organic compounds (VOCs) at the Sonnblick Observatory. Austria (31 06 m a.s.l.) were measured in autumn 1999 using proton-transfer-reaction ma ss spectrometry (PTR-MS). Anthropogenic VOCs at this remote site, such as b enzene and toluene (50 pptv to 2 ppbv), were primarily traced to air from u rban areas. In mid-November, following a hard freeze in the central Alps, a different pattern of VOCs developed similar to that seen with C5 and C6 le af wound compounds (0.5 to 5 ppbv range). The common origins of these compo unds are proposed to be freeze-damaged leaves, inferred from laboratory inv estigations that identified hexenals, hexanal, methylbutanals, pentenol and pentenone formation in such leaves. We suggest that deciduous forests can release large amounts of reactive VOCs during the autumn, and that these re leases may be important for regional tropospheric chemistry.