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

Seasonal variations of biogenic volatile organic compound (VOC) emission rates and standardised emission factors from gorse (Ulex europaeus) have been measured at two sites in the United Kingdom, from October 1994 to September 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 compound with a relative composition fluctuating from 7% of the total VOC (winter) to 97% (late summer). The monoterpenes x-pinene, camphene, sabinene, beta -pinene, myrcene, limonene, trans-ocimene and gamma -terpinene were also emitted, with x-pinene being the dominant monoterpene during most the year. Trans-ocimene represented 33-66% of the total monoterpene during the hottest months from June to September. VOC emissions were found to be accurately predicted using existing algorithms. Standard (normalised) emission factors of VOCs from gorse were calculated using experimental parameters measured 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, respectively, 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 variations with respect to temperature and light intensity. The effects of using inappropriate algorithms to derive VOC fluxes from gorse were assessed for isoprene and monoterpenes. Although on an annual basis the discrepancies are not significant, monthly estimation of isoprene were found to be overestimated by more than a factor of 50 during wintertime when the seasonality of emission factors is not considered. (C) 2001 Elsevier Science Ltd. All rights reserved.