Plants and microorganisms produce a variety of organic and inorganic compounds that react with photochemical components of the atmosphere and influence the production and turnover of atmospheric oxidants. 1 It is this continuous processing of reactive compounds from various terrestrial and marine ecosystems that maintains the atmosphere in a state of chemical disequilibrium and sustains some key atmospheric components that are required for life to persist. For example, most of the molecular oxygen (O 2 ) that exists in the atmosphere, and is used as an electron acceptor in aerobic respiration, is derived from autotrophic photosynthesis. Tropospheric O 2 , in turn, sustains the production of stratospheric ozone (O 3 ), a compound that protects nucleic acids, the compounds that carry the genetic code for life, from potentially harmful fluxes of ultraviolet radiation. There is clearly need for a coupled, synthetic view of biology and chemistry in order to completely understand atmospheric biogeochemical dynamics and their role in the sustenance of life.
In this chapter, I focus on the emission of biogenic volatile organic compounds (BVOCs), principally by plants, and their photochemical fate in the atmosphere. The diversity of BVOCs capable of fuelling atmospheric chemistry is immense, including alkenes, alkanes, alcohols, aldehydes, ketones and organic acids. These compounds exhibit a broad range of atmospheric lifetimes, ranging from a few seconds to several years. Ultimately, they all represent sources of electrons that exist at higher potential energy levels than those in the fundamental inorganic products to which they are oxidized (e.g. CO 2 ) and, thus, thermo-
The Chemistry and Biology of Volatiles
Edited by Andreas Herrmann