Four-dimensional variational inversion of black carbon emissions during ARCTAS-CARB with WRFDA-Chem
Biomass burning emissions of atmospheric aerosols, including black carbon, are growing due to increased global drought, and comprise a large source of uncertainty in regional climate and air quality studies. We develop and apply new incremental four-dimensional variational (4D-Var) capabilities i...
Main Authors: | , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-06-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | http://www.atmos-chem-phys.net/17/7605/2017/acp-17-7605-2017.pdf |
Summary: | Biomass burning emissions of atmospheric aerosols, including black carbon,
are growing due to increased global drought, and comprise a large source of
uncertainty in regional climate and air quality studies. We develop and apply
new incremental four-dimensional variational (4D-Var) capabilities in
WRFDA-Chem to find optimal spatially and temporally distributed biomass
burning (BB) and anthropogenic black carbon (BC) aerosol emissions. The
constraints are provided by aircraft BC concentrations from the Arctic
Research of the Composition of the Troposphere from Aircraft and Satellites
in collaboration with the California Air Resources Board (ARCTAS-CARB) field
campaign and surface BC concentrations from the Interagency Monitoring of
PROtected Visual Environment (IMPROVE) network on 22, 23, and 24 June 2008.
We consider three BB inventories, including Fire INventory from NCAR (FINN)
v1.0 and v1.5 and Quick Fire Emissions Database (QFED) v2.4r8. On 22 June,
aircraft observations are able to reduce the spread between a customized QFED
inventory and FINNv1.0 from a factor of 3. 5 ( × 3. 5) to only
× 2. 1. On 23 and 24 June, the spread is reduced from × 3. 4 to
× 1. 4. The posterior corrections to emissions are heterogeneous in time
and space, and exhibit similar spatial patterns of sign for both inventories.
The posterior diurnal BB patterns indicate that multiple daily emission peaks
might be warranted in specific regions of California. The US EPA's 2005
National Emissions Inventory (NEI05) is used as the anthropogenic prior. On
23 and 24 June, the coastal California posterior is reduced by × 2,
where highway sources dominate, while inland sources are increased near
Barstow by × 5. Relative BB emission variances are reduced from the
prior by up to 35 % in grid cells close to aircraft flight paths and by
up to 60 % for fires near surface measurements. Anthropogenic variance
reduction is as high as 40 % and is similarly limited to sources close to
observations. We find that the 22 June aircraft observations are able to
constrain approximately 14 degrees of freedom of signal (DOF), while surface
and aircraft observations together on 23/24 June constrain 23 DOF. Improving
hourly- to daily-scale concentration predictions of BC and other aerosols
during BB events will require more comprehensive and/or targeted measurements
and a more complete accounting of sources of error besides the emissions. |
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ISSN: | 1680-7316 1680-7324 |