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A. Guenther et al.
incorporated into the database and currently are the best approach for constraining
monoterpene emission factors.
29.4 MEGAN3 Sensitivity and Evaluation
A comparison of MEGAN2.1 and MEGAN3, with the emission factors generated by
the initial runs of the MEGAN-EFP, indicated that the MEGAN3 isoprene emissions
were considerably lower than MEGAN2.1 and in better agreement with aircraft flux
and concentration measurements. Generally, there was a reduction in monoterpene
emissions calculated in MEGAN3 relative to MEGAN2.1 that degraded agreement.
Concentration comparisons using the Comprehensive Air Quality Model with extensions [6] indicated that estimates of monoterpenes aloft were often considerably lower
using the MEGAN3 estimates. The cause of the reduction of monoterpene emissions
in MEGAN3 is not known, but is under investigation. Assessment of the new stress
algorithms (high temperature, low temperature, high winds, high ozone) incorporated into MEGAN3 indicated that there was relatively little impact on isoprene and
monoterpenes using the initial parameterizations that are a conservative representation of these processes. These stresses are expected to have a greater impact on other
BVOC.
29.5 Conclusions
MEGAN3 can be used to provide biogenic emissions estimates that are more accurate
than MEGAN2.1 as demonstrated by comparison to aircraft flux measurements.
MEGAN3 also facilitates assessing and improving individual model components
including emission factors, canopy and soil environment conditions, and response
functions which should lead to improvements over alternative models that are based
on outdated emission factors and model algorithms.
The MEGAN3 framework can be used for assessing available landcover and
emissions data and identifying gaps. The available landcover and emissions data that
were incorporated for the initial database used for this project improved isoprene
emissions for the regions investigated by the 2013 SAS aircraft study. Discrepancies
between enclosure and aircraft measurements of isoprene emissions were reconciled.
Distributions of tree species, the major source of isoprene and monoterpene emissions, can be adequately estimated with existing landcover data in forested regions of
southeast and southcentral US. Additional efforts are needed to improve tree species
distributions in urban and savannah locations. Isoprene and other VOC emission
studies have focused on closed canopy forests. The performance of models in open
canopies in savannas and shrublands has not been well characterized and the existing landcover data, canopy environment and isoprene response functions may not be
suitable for these landscapes.
A. Guenther et al.
incorporated into the database and currently are the best approach for constraining
monoterpene emission factors.
29.4 MEGAN3 Sensitivity and Evaluation
A comparison of MEGAN2.1 and MEGAN3, with the emission factors generated by
the initial runs of the MEGAN-EFP, indicated that the MEGAN3 isoprene emissions
were considerably lower than MEGAN2.1 and in better agreement with aircraft flux
and concentration measurements. Generally, there was a reduction in monoterpene
emissions calculated in MEGAN3 relative to MEGAN2.1 that degraded agreement.
Concentration comparisons using the Comprehensive Air Quality Model with extensions [6] indicated that estimates of monoterpenes aloft were often considerably lower
using the MEGAN3 estimates. The cause of the reduction of monoterpene emissions
in MEGAN3 is not known, but is under investigation. Assessment of the new stress
algorithms (high temperature, low temperature, high winds, high ozone) incorporated into MEGAN3 indicated that there was relatively little impact on isoprene and
monoterpenes using the initial parameterizations that are a conservative representation of these processes. These stresses are expected to have a greater impact on other
BVOC.
29.5 Conclusions
MEGAN3 can be used to provide biogenic emissions estimates that are more accurate
than MEGAN2.1 as demonstrated by comparison to aircraft flux measurements.
MEGAN3 also facilitates assessing and improving individual model components
including emission factors, canopy and soil environment conditions, and response
functions which should lead to improvements over alternative models that are based
on outdated emission factors and model algorithms.
The MEGAN3 framework can be used for assessing available landcover and
emissions data and identifying gaps. The available landcover and emissions data that
were incorporated for the initial database used for this project improved isoprene
emissions for the regions investigated by the 2013 SAS aircraft study. Discrepancies
between enclosure and aircraft measurements of isoprene emissions were reconciled.
Distributions of tree species, the major source of isoprene and monoterpene emissions, can be adequately estimated with existing landcover data in forested regions of
southeast and southcentral US. Additional efforts are needed to improve tree species
distributions in urban and savannah locations. Isoprene and other VOC emission
studies have focused on closed canopy forests. The performance of models in open
canopies in savannas and shrublands has not been well characterized and the existing landcover data, canopy environment and isoprene response functions may not be
suitable for these landscapes.