Seasonal variations in VOC emission rates from gorse (Ulex europaeus)

Seasonal variations of biogenic volatile organic compound (VOC) emission ra tes and standardised emission factors from gorse (Ulex europaeus) have been measured at two sites in the United Kingdom, from October 1994 to Septembe r 1995, within temperature and PAR conditions ranging from 3 to 34 C and 10 -1300 mu mol m(-2) s(-1), respectively. Isoprene was the dominant emitted c ompound with a relative composition fluctuating from 7% of the total VOC (w inter) to 97% (late summer). The monoterpenes x-pinene, camphene, sabinene, beta -pinene, myrcene, limonene, trans-ocimene and gamma -terpinene were a lso emitted, with x-pinene being the dominant monoterpene during most the y ear. Trans-ocimene represented 33-66% of the total monoterpene during the h ottest months from June to September. VOC emissions were found to be accura tely predicted using existing algorithms. Standard (normalised) emission fa ctors of VOCs from gorse were calculated using experimental parameters meas ured during the experiment and found to fluctuate with season, from 13.3+/- 2.1 to 0.1+/-0.1 mu gC (gdwt)(-1) h(-1) in August 1995 and January 1995, re spectively, for isoprene, and from 2.5 +/- 0.2 to 0.4 +/- 0.2 mug C (g dwt) (-1) h(-1) in July and November 1995, respectively, for total monoterpenes. No simple clear relation was found to allow prediction of these seasonal v ariations with respect to temperature and light intensity. The effects of u sing inappropriate algorithms to derive VOC fluxes from gorse were assessed for isoprene and monoterpenes. Although on an annual basis the discrepanci es are not significant, monthly estimation of isoprene were found to be ove restimated by more than a factor of 50 during wintertime when the seasonali ty of emission factors is not considered. (C) 2001 Elsevier Science Ltd. Al l rights reserved.