Determination and accuracy of VOC-fluxes above the pine/oak forest at Castelporziano

Concentrations of alpha-pinene, beta-pinene and limonene were determined as two or three point profiles above the mediterranean pine/oak forest at Castelporziano, Italy. Based on these, as well as on micrometeorological data, the fluxes of these compounds were estimated using the modified Bowen-ratio method and a log-profile fit. The accuracy of the calculated fluxes was estimated, resulting in errors around 50%, which were mainly produced by the relatively small concentration gradients observed. The dependence of emission fluxes on surface temperature was interpolated by three equations of the form F(T) = F-s exp(beta . (T - T-s)) for the three compounds. The three resulting temperature exponents beta were significantly greater than the value for monoterpenes given by Guenther et al. (1993, J. Geophysical Research 18, 12,609-12,617). It is also greater than the corresponding value derived by Bertin et al. (1997, Atmospheric Environment) from the isoprene model of Guenther et al. (1993, J. Geophysical Research 18, 12,609-12,617). (C) 1997 Elsevier Science Ltd.