Evaluation of regional isoprene emission factors and modeled fluxes in California
Author
Misztal, Pawel K.
Avise, Jeremy C.
Karl, Thomas
Scott, Klaus
Jonsson, Haflidi H.
Guenther, Alex B.
Goldstein, Allen H.
Date
2016-08-02Metadata
Show full item recordAbstract
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.
Description
The article of record as published may be located at http://dx.doi.org/10.5194/acp-16-9611-2016
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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