Journal of Atmospheric Chemistry 33: 23–88, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.
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Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology J. KESSELMEIER? and M. STAUDT Max Planck Institute for Chemistry, Department Biogeochemistry, PO Box 3060, D-55020 Mainz, Germany; E-mail:
[email protected] (Received: 20 March 1998; accepted: 21 October 1998) Abstract. This overview compiles the actual knowledge of the biogenic emissions of some volatile organic compounds (VOCs), i.e., isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls, and acids. We discuss VOC biosynthesis, emission inventories, relations between emission and plant physiology as well as temperature and radiation, and ecophysiological functions. For isoprene and monoterpenes, an extended summary of standard emission factors, with data related to the plant genus and species, is included. The data compilation shows that we have quite a substantial knowledge of the emission of isoprene and monoterpenes, including emission rates, emission regulation, and biosynthesis. The situation is worse in the case of numerous other compounds (other VOCs or OVOCs) being emitted by the biosphere. This is reflected in the insufficient knowledge of emission rates and biological functions. Except for the terpenoids, only a limited number of studies of OVOCs are available; data are summarized for alkanes, alkenes, carbonyls, alcohols, acids, and esters. In addition to closing these gaps of knowledge, one of the major objectives for future VOC research is improving our knowledge of the fate of organic carbon in the atmosphere, ending up in oxidation products and/or as aerosol particles. Key words: nonmethane hydrocarbons, volatile organic compounds, terpenes, isoprene, oxygenated compounds, alkanes, alkenes, carbonyls, acids, esters, emission, physiology, ecology, emission inventories, review.
1. Introduction The term biogenic volatile organic compounds (biogenic VOCs) includes organic atmospheric trace gases other than carbon dioxide and monoxide. Focusing on hydrocarbons but excluding methane, the term nonmethane hydrocarbons (NMHCs) is used, while VOCs without methane are termed nonmethane VOCs (NMVOCs). Hence, large numbers of groups of saturated, unsaturated, and oxygenated derivatives are included within VOCs. Biogenic VOCs include the isoprenoids (isoprene and monoterpenes) as well as alkanes, alkenes, carbonyls, alcohols, esters, ethers, and acids. Emission inventories show isoprene and monoterpenes as the most prominent compounds. Alcohols and carbonyls follow the isoprenoids as the most predominant groups. The release of compounds other than isoprenoids has ? Author for correspondence.
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J. KESSELMEIER AND M. STAUDT
Table I. Comparison of nonmethane volatile organic compound (NMVOC) categories (Goldan et al., 1993; Guenther et al., 1995; Neeb et al., 1997; Singh et al., 1994) Name
Chemical lifetimesa Day Night
Example
Atmospheric concentrations
Isoprene
3 hrs
1.5 hrs
isoprene
ppt to several ppb
Monoterpenes
2–3 hrs 40–80 min 15–20 min
