The Long Reach of Biogenic Emissions in the Atmosphere
This chapter provides a brief summary of the impacts of biogenic emissions in the atmosphere, focusing on reactive organics. These species have a significant impact on the chemical balance of the troposphere and also affect the formation of ozone and othe
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Abstract This chapter provides a brief summary of the impacts of biogenic emissions in the atmosphere, focusing on reactive organics. These species have a significant impact on the chemical balance of the troposphere and also affect the formation of ozone and other secondary species in polluted regions. Methane, though slowly reacting, also plays an important role in the chemistry of the global troposphere. Methane and aerosol production from biogenic organics both affect climate. Two distinctions are emphasized: (i) between naturally occurring emissions from largely unperturbed ecosystems (usually forests) as opposed to emissions associated with agriculture and other human activities; and (ii) between reactive emissions (including slowly reacting species) and completely nonreactive species such as carbon dioxide. The reactive species are eventually removed from the atmosphere, but carbon dioxide and other nonreactive species accumulate in the atmosphere over time and are only removed on time scales of 100 years or longer.
It is widely known that emissions from the biosphere have a large effect on the evolution of the atmosphere. Most immediately, respiration of CO2 and exhale of O2 by plants causes a noticeable seasonal atmospheric cycle, with CO2 decreasing during the northern summer at the time of maximum net photosynthesis on a global scale. In addition to the global cycle, the biosphere represents a reservoir of carbon that can be exchanged with atmospheric CO2, with time scales ranging from years (for most plant species) to centuries (for stored carbon in soils). On geologic time scales the evolution of the biosphere is directly associated with release of free oxygen (O2) to the atmosphere, and even today the reservoir of atmospheric oxygen turns over on a time scale of approximately 25 million years. The increase in atmospheric
S. Sillman (*) Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA e-mail: [email protected] T. Fenning (ed.), Challenges and Opportunities for the World’s Forests in the 21st Century, Forestry Sciences 81, DOI 10.1007/978-94-007-7076-8_32, © Springer Science+Business Media Dordrecht 2014
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oxygen over geologic time (from
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