Characterization of speciated aerosol direct radiative forcing over California
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Transcript of Characterization of speciated aerosol direct radiative forcing over California
Chun Zhao, L. Ruby Leung, Richard EasterPacific Northwest National Laboratory, Richland, WA, USA
Jenny HandColorado State University, Fort Collins, CO, USA
Jeremy AviseCalifornia Air Resources Board, CA, USA
13th WRF Users' Workshop Boulder, Colorado, June 28, 2012
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Characterization of speciated aerosol direct radiative forcing over California
Aerosol impact over California
California is one of the most polluted regions in the world,
with air quality that is likely affecting well-being of people.
Air pollution control reduced aerosol concentrations, which
has potential to cause an increase in solar radiation and
weaken the aerosol effect of regional climate change
mitigation.
Understanding the seasonal variation and speciation of
aerosol and its direct radiative forcing over California is
important to provide further information as guidance for future
emission control strategies.
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WRF-Chem MADE/SORGAM aerosol scheme (Modal) coupled with
GOCART dust emission scheme [Ginoux et al., 2001, Zhao et
al., 2010].
Aerosol SW and LW direct radiative effects coupled with RRTMG radiation schemes [Zhao et al., 2011].
Morrison microphysics scheme and Grell convective scheme
12km horizontal resolution; simulation for 2005; driven by NARR reanalysis
ARCTAS-CARB anthropogenic emission inventory for June 2008; GFEDv3 biomass burning emission inventory for 2005
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Aerosols in the model are assumed internally mixed.
A methodology is developed to diagnose the optical depth and
direct radiative forcing of individual aerosol species:
AOD[species i] = AOD[all-species] – AOD[without species i]
Forcing[species i] = Forcing[all-species] – Forcing[without species i]
Optical properties and direct radiative forcing for OM, EC, dust,
sulfate, and a single group lumping all other aerosol species
are estimated.
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Spatial correlation coefficient and mean bias: 2m T: 0.90-0.94 with mean bias < 2 oC2m RH: 0.7~0.9 with mean bias < ~0.1Rain: 0.5-0.8 with mean bias < ~10 mm/monthSolar radiation: 0.98
EPA (urban): triangles (100)
IMPROVE (rural): circles (40)
High total PM2.5 over the
Central Valley (CV) and the
Los Angeles metropolitan
regions (LA)Seasonality with highest in
winter and lowest in
summer Model captures the spatial
distribution and seasonality;
and high PM2.5
concentrations over
southeastern California (due
to dust)
Low emission?Resolution?
Low emission?Resolution?SOA?
Doubled EC
Photochemistry Gas-aerosol partition
High bias nearby the source regionResolution?
High bias nearby the coastal areasEmission scheme? Measurements?
2008 for 2005?
Improve speciation profiles
High AOD and
AAOD over the CV,
LA, and the deserts
Higher AOD/AAOD
over the CV and the
LA than over the
deserts
More distinct
seasonality of
AOD/AAOD over
the CV and the LA
than over the
deserts
ECx2 simulation
Differences between the diagnosed and simulated AOD and AAOD:
non-linear interactions among the internal-mixed aerosol species
AOD: winter maximum and fall minimum, determined by that of
anthropogenic aerosols. Sulfate AOD is largest. The AOD for EC and
OM is small, but may have low biases.
AAOD: summer maximum and winter minimum, determined by EC and
dust. Aerosol species other than EC and dust also enhance the
absorption and account for 15-20% of AAOD.
Non-linear interactions
TOA: most aerosols-
negative radiative
forcing, except EC
Atmosphere: EC and
dust are biggest
contributors (~90%) to
warming; Internal
mixing enhances
warming.
Surface: all aerosols
have a cooling effect.
EC is the largest
contributor in summer,
while sulfate is in
winter.
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Summary WRF-Chem captures the observed seasonal meteorological
conditions over California.
WRF-Chem reproduces the observed spatial and seasonal distribution of most aerosol species, except underestimating the surface concentrations of OM and EC, potentially due to uncertainties or/and interannual variabilities of the anthropogenic emissions of OM and EC and the outdated SOA mechanism. A sensitivity simulation with anthropogenic EC emission doubled significantly reduces the model low bias of EC.
The seasonality of aerosol surface concentration is mainly determined by vertical turbulent mixing, ventilation, and photochemical activity, with distinct characteristics for individual aerosol species and between urban and rural areas.
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Summary Anthropogenic aerosols dominate the aerosol optical depth (AOD).
The ratio of AOD to AAOD shows distinct seasonality with a winter
maximum and a summer minimum.
On statewide average over California, aerosol reduces the seasonal-
average surface radiation fluxes by about 3 W m-2 with a maximum
of 10 W m-2 in summer. In the atmosphere, aerosol introduces a
warming effect of about 2 W m-2 with a maximum of 10 W m-2 also in
summer, with EC and dust as the main contributors (about 90%). At
the TOA, the overall aerosol direct radiative effect is cooling with a
maximum of -3.5 W m-2. EC contributes exclusively to the TOA
warming of up to about 0.7 W m-2.
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Extra
Impact of BC emission control (1980’s~2000’s)
Clear Sky All Sky
Solar Radiation at Surface
Impact of BC emission control (1980’s~2000’s)
Surface Temperature Atmospheric Heating
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