Biogenic volatile organic compound emissions from a lowland tropical wet forest in Costa Rica

Atmospheric Environment 36 (2002) 3793–3802 Biogenic volatile organic compound emissions from a lowland tropical wet forest in Costa Rica Chris Geron a, *, Alex Guenther b , Jim Greenberg b , Henry W. Loescher c , Deborah Clark d , Brad Baker e a National Risk Management Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, NC 27711, USA b National Center for Atmospheric Research, Boulder, CO 80303, USA c School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, USA d Department of Biology, University of Missouri-St. Louis, St. Louis, MS 63121, USA e South Dakota School of Mines and Technology, Rapid City, SD 57701, USA Received 10 August 2001; accepted 17 April 2002 Abstract Twenty common plant species were screened for emissions of biogenic volatile organic compounds (BVOCs) at a lowland tropical wet forest site in Costa Rica. Ten of the species examined emitted substantial quantities of isoprene. These species accounted for 35–50% of the total basal area of old-growth forest on the major edaphic site types, indicating that a high proportion of the canopy leaf area is a source of isoprene. A limited number of canopy-level BVOC ﬂux measurements were also collected by relaxed eddy accumulation (REA). These measurements verify that the forest canopy in this region is indeed a signiﬁcant source of isoprene. In addition, REA ﬂuxes of methanol and especially acetone were also signiﬁcant, exceeding model estimates and warranting future investigation at this site. Leaf monoterpene emissions were non-detectable or very low from the species surveyed, and ambient concentrations and REA ﬂuxes likewise were very low. Although the isoprene emission rates reported here are largely consistent with phylogenetic relations found in other studies (at the family, genus, and species levels), two species in the family Mimosaceae, a group previously found to consist largely of non-isoprene emitters, emitted signiﬁcant quantities of isoprene. One of these, Pentaclethra macroloba (Willd.) Kuntze, is by far the most abundant canopy tree species in the forests of this area, composing 30–40% of the total basal area. The other, Zygia longifolia (Humb. & Bonpl.) Britton & Rose is a common riparian species. Our results suggest that the source strength of BVOCs is important not only to tropical atmospheric chemistry, but also may be important in determining net ecosystem carbon exchange. Published by Elsevier Science Ltd. Keywords: Isoprene; Biogenic volatile organic compounds; Relaxed eddy accumulation; Pentaclethra macroloba; Palmae; La selva biological station 1. Introduction Isoprene emission from vegetation is the world’s largest known source of non-methane volatile organic *Corresponding author. Tel.: +1-919-541-4639; fax: +1- E-mail address: geron.chris@epa.gov (C. Geron). 1352-2310/02/$ - see front matter Published by Elsevier Science Ltd. PII: S 1 3 5 2 - 2 3 1 0 ( 0 2 ) 0 0 3 0 1 - 1 compounds (NMVOCs). Its importance is further ampliﬁed by its high reactivity with the hydroxyl radical compared to other abundant atmospheric NMVOCs. It is estimated that over 90% of isoprene emission is from vegetation (Guenther et al., 1995). Modeling (Guenther et al., 1995) and limited measurement (Guenther et al., 1999, 1996) studies have suggested that at least 50% of the global annual isoprene ﬂux is from tropical