Terpene, forest emission

Forests can act as sources of some of the trace gases in the atmosphere, such as hydrocarbons, hydrogen sulfide, NO, and NH3. Forests have been identified as emitters of terpene hydrocarbons. In 1960, Went (10) estimated that hydrocarbon releases to the atmosphere were on the order of 108 tons per year. Later work by Rasmussen (11) suggested that the release of terpenes from forest systems is 2 x 10 tons of reactive materials per year on a global basis. This is several times the anthropogenic input. Yet, it is important to remember that forest emissions are much more widely dispersed and less concentrated than anthropogenic emissions. Table 8-2 shows terpene emissions from different types of forest systems in the United States. 

Yokouchi et al., 1983). Micrometeorological conditions also are important in controlling the concentrations of forest emissions. For example, Isidorov et al. (1985) noted that a stable atmospheric stratification in the evening caused a considerable enhancement of terpene concentrations. 

Composition of U.S. Forest-Type Groups by Foliar Terpene Emissions... 

Baumann, M.G.D., Batterman, S.A. and Zhang, G.-Z. (1999) Terpene emissions from particleboard and medium-density fiberboard products. Forest Products Journal, 49 (1), 49-56. 

There definitely are very large emissions of higher hydrocarbons from plants, including ethylene. This has been definitely discovered above the tropical forests in Brazil. The most active emissions are actually isoprene and the terpenes, but there are many other hydrocarbons which are chemically very reactive. 

The biosphere is a major contributor to the atmosphere of heavier hydrocarbons. Fritz Went (8, 9), who first recognized the global extent of smog, pointed out the general importance of natural emissions from vegetation. He estimated that sources in the biosphere annually emit between 170 X 10 and 10 tons of hydrocarbon material to the atmosphere. Went also observed that these materials are mainly in the terpene class and that, because they are photochemically reactive, these materials are polymerized in atmospheric photochemical reactions to form an organic aerosol. He attributes the blue haze found in many forested areas to the optical effects of this aerosol. 

In addition to the important role biogenic terpenes play in gas-hase chemistry, their impact also extends to heterogeneous air chemistry. Although Went (1960) linked the formation of the blue haze over coniferous forests to the biogenic emission of 20 monoterpenes over 40 years ago, it was not until recently that terpenes received their due attention with respect to their role in secondary organic aerosol (SOA) formation. O Dowd et al. (2002) reported that nucleation events over a boreal forest were driven by the condensation of terpene oxidation products. Formaldehyde (HCHO) is a high-yield product of isoprene oxidation. The short photochemical lifetime of HCHO allows the observation of this trace gas to help constrain isoprene emissions (Shim et al. 2005). 

It has been suggested that volatile terpenes play a similar dual action inside the leaves and participate in ozone quenching in the intercellular spaces before they are released into the atmosphere. In plants exposed to ozone either a reduction or an increase of isoprene and monoterpene emission is observed. Particularly high ozone concentrations induce the terpene emission often as a result of cellular damage. There is evidence that volatile terpenes are able to reduce ozone damage and to quench ozone and reactive oxygen species (ROS). Furthermore, it has been demonstrated in tropical forests a large fraction of total plant sesquiterpene... 

VOC). Of most concern is the emission of terpenes. Terpenes are hydrocarbons present in conifer oleo-resins. They could also be found in many hardwoods, especially of tropic origin. Natural emissions take place everywhere in our forests and the quantity released naturally is much higher than the anthropogenic emissions. The problem with the latter is the very high local concentrations that can be achieved. Terpenes have a high reactivity in the atmosphere and may contribute to the formation of ground-level ozone. 

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