64 lines
3.2 KiB
ReStructuredText
64 lines
3.2 KiB
ReStructuredText
.. _rst_Biogenic Volatile Organic Compounds (BVOCs):
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Biogenic Volatile Organic Compounds (BVOCs)
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===============================================
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This chapter briefly describes the biogenic volatile organic compound
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(BVOC) emissions model implemented in CLM. The CLM3 version (Levis et
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al. 2003; Oleson et al. 2004) was based on Guenther et al. (1995). Heald
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et al. (2008) updated this scheme in CLM4 based on Guenther et al.
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(2006). The current version was implemented in CLM4.5 and is based on MEGAN2.1 discussed in
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detail in Guenther et al. (2012). This update of MEGAN incorporates four
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main features: 1) expansion to 147 chemical compounds, 2) the treatment of the
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light-dependent fraction (LDF) for each compound, 3) inclusion of the
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inhibition of isoprene emission by atmospheric CO\ :sub:`2` and
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4) emission factors mapped to the specific PFTs of the CLM.
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MEGAN2.1 now describes the emissions of speciated monoterpenes,
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sesquiterpenes, oxygenated VOCs as well as isoprene. A flexible scheme
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has been implemented in the CLM to specify a subset of emissions. This
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allows for additional flexibility in grouping chemical compounds to form
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the lumped species frequently used in atmospheric chemistry. The mapping
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or grouping is therefore defined through a namelist parameter in
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drv\_flds\_in, e.g. megan\_specifier = ’ISOP = isoprene’, ’BIGALK =
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pentane + hexane + heptane + tricyclene’.
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Terrestrial BVOC emissions from plants to the atmosphere are expressed
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as a flux, :math:`F_{i}` (:math:`\mu` \ g C m\ :sup:`-2` ground area h\ :sup:`-1`), for emission of chemical compound
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:math:`i`
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.. math::
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:label: ZEqnNum964222
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F_{i} =\gamma _{i} \rho \sum _{j}\varepsilon _{i,j} \left(wt\right)_{j}
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where :math:`\gamma _{i}` is the emission activity factor accounting
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for responses to meteorological and phenological conditions,
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:math:`\rho` is the canopy loss and production factor also known as
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escape efficiency (set to 1), and :math:`\varepsilon _{i,\, j}`
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(:math:`\mu` \ g C m\ :sup:`-2` ground area h\ :sup:`-1`) is
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the emission factor at standard conditions of light, temperature, and
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leaf area for plant functional type *j* with fractional coverage
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:math:`\left(wt\right)_{j}` (Guenther et al. 2012). The emission
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activity factor :math:`\gamma _{i}` depends on plant functional type,
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temperature, LAI, leaf age, and soil moisture (Guenther et al. 2012).
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For isoprene only, the effect of CO\ :sub:`2` inhibition is now
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included as described by Heald et al. (2009). Previously, only isoprene
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was treated as a light-dependent emission. In MEGAN2.1, each chemical
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compound is assigned a LDF (ranging from 1.0 for isoprene to 0.2 for
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some monoterpenes, VOCs and acetone). The activity factor for the light
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response of emissions is therefore estimated as:
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.. math::
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:label: 28.2)
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\gamma _{P,\, i} =\left(1-LDF_{i} \right)+\gamma _{P\_ LDF} LDF_{i}
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where the LDF activity factor (:math:`\gamma _{P\_ LDF}` ) is specified
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as a function of PAR as in previous versions of MEGAN.
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The values for each emission factor :math:`\epsilon _{i,\, j}` are
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now available for each of the plant functional types in the CLM and
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each chemical compound. This information is distributed through an
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external file, allowing for more frequent and easier updates.
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