**1. Introduction**

Nonmethane volatile organic compounds (NMOCs) represent a key class of chemical species governing global tropospheric chemistry and the global carbon cycle (Fehsenfeld et al. 1992; Singh and Zimmerman 1992). The most important anthropogenic sources of hydrocarbons include fossil fuel combustion, direct release from industry, industrial processing of chemicals, and waste. The global estimated anthropogenic hydrocarbon flux is 1.0 × 1014 gC per year (Singh and Zimmerman 1992). Biological processes in both marine and terrestrial environments contribute to biogenic hydrocarbon sources. For the terrestrial biosphere, the principal hydrocarbon sources come from vegetation. In regions such as eastern North America, biogenic hydrocarbon emission rate estimates exceed anthropogenic emissions (Guenther et al. 1994). At the global scale it is estimated that vegetation emits 1.2 × 1015 gC per year, an amount equivalent to global methane emissions (Guenther et al. 1995).

Much of the recent work on emissions of biogenic volatile organic compounds (BVOCs) has focused on isoprene. However, in regions dominated by coniferous or non-isoprene emitting deciduous tree species, monoterpenes may dominate BVOC emissions. Monoterpenes comprise a significant portion of BVOC emissions (Guenther et al., 1995; Pio and Valente, 1998), and it is important to understand the atmospheric fates of monoterpenes and their oxidation products. The emission patterns of the various monoterpenes strongly depend on the type of vegetation and on the environmental conditions, however d-limonene makes up the majority of monoterpene emissions over orange groves, while α-pinene and βpinene dominate over most other kinds of forests, especially those composed of oaks and conifers (Pio and Valente, 1998; Christensen et al., 2000). In recent years, the number of relevant studies has increased substantially, necessitating the review of this topic, including emission fluxes of monoterpenes, the effects of species and nutrient limitation on emissions, secondary organic aerosol yields via condensation and nucleation.

© 2012 Ma licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Ma, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
