Evaluation of regional isoprene emission factors and modeled fluxes in California
Accurately modeled biogenic volatile organic compound (BVOC) emissions are an essential input to atmospheric chemistry simulations of ozone and particle formation. BVOC emission models rely on basal emission factor (BEF) distribution maps based on emission measurements and vegetation land-cover...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/9611/2016/acp-16-9611-2016.pdf |
| Summary: | Accurately modeled biogenic volatile organic compound (BVOC) emissions are an
essential input to atmospheric chemistry simulations of ozone and particle
formation. BVOC emission models rely on basal emission factor (BEF)
distribution maps based on emission measurements and vegetation land-cover
data but these critical input components of the models as well as model
simulations lack validation by regional scale measurements. We directly assess
isoprene emission-factor distribution databases for BVOC emission models by
deriving BEFs from direct airborne eddy covariance (AEC) fluxes
(Misztal et al., 2014) scaled to the surface and normalized by the activity
factor of the Guenther et al. (2006) algorithm. The available airborne BEF data
from approx. 10 000 km of flight tracks over California were averaged
spatially over 48 defined ecological zones called ecoregions. Consistently,
BEFs used by three different emission models were averaged over the same
ecoregions for quantitative evaluation. Ecoregion-averaged BEFs from the most
current land cover used by the Model of Emissions of Gases and Aerosols from
Nature (MEGAN) v.2.1 resulted in the best agreement among the tested
land covers and agreed within 10 % with BEFs inferred from measurement.
However, the correlation was sensitive to a few discrepancies (either
overestimation or underestimation) in those ecoregions where land-cover BEFs
are less accurate or less representative for the flight track. The two other
land covers demonstrated similar agreement (within 30 % of measurements) for
total average BEF across all tested ecoregions but there were a larger number
of specific ecoregions that had poor agreement with the observations.
Independently, we performed evaluation of the new California Air Resources
Board (CARB) hybrid model by directly comparing its simulated isoprene area
emissions averaged for the same flight times and flux footprints as actual
measured area emissions. The model simulation and the observed surface area
emissions agreed on average within 20 %. We show that the choice of model
land-cover input data has the most critical influence on model-measurement
agreement and the uncertainty in meteorology inputs has a lesser impact at
scales relevant to regional air quality modeling. |
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| ISSN: | 1680-7316 1680-7324 |