Linking Anthropogenic Aerosols, Urban Air Pollution and Tropospheric Chemistry to Climate (actually, to CAM/CCSM)
Chien WangMassachusetts Institute of Technology
Current and Future Researches
Impacts of Tropospheric Chemistry and Aerosols on Climatic Impacts of Tropospheric Chemistry and Aerosols on Climatic and Environmental Changeand Environmental Change
• Radiative forcings of CH4 and tropospheric O3
• Radiative forcing and influence on hydrological cycle of aerosols
• Air pollution, acid deposition, and pollutant cleaning
Impacts of Climatic Change on Tropospheric Chemistry Impacts of Climatic Change on Tropospheric Chemistry and Aerosolsand Aerosols
• Temperature, UV fluxes, and H2O(g) on reaction rates
• Cloud and precipitation processing of gases and aerosols
• Clouds on aerosols’ effective climate impacts
Why do we need an interactive model
Basic requirement for the interactive model
A good balance of the process complexity (including needed important processes and parameters) and model performance (accomplishing runs of 50-100 years with a practical turnaround time)
Importance of Aerosols’ Chemical Compositions:
JJA
DJF
-1000 10000-500 500 (mm/yr/grid)
BC Caused Changes in Convective Precipitation Rate(Using the last 20-year means of two 60-year runs coupled with SOM; Wang, 2004)
Maximum Coverage of Cloud vs.
Initial CCN Concentration
Total Precipitation vs.
Initial CCN Concentration
0 1000 2000 3000 4000 5000 60000
10
20
30
40
50
Clo
ud C
over
age
(%)
Initial CCN Concentration (1/cc)0 1000 2000 3000 4000 5000 6000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Tota
l Pre
cipi
tatio
n (m
m)
Initial CCN Concentration (1/cc)
Importance of Aerosols’ Number Concentration:Results from Thirty 3-D cloud-resolving model runs (Wang, 2004a&b)
Importance of Aerosols’ Size Distribution: Results of Size-Resolving Aerosol Model (Ekman et al., 2004)
Note: Observed. max. value (>7nm) in anvil: 2.5·104 Modeled max. value (>6nm) in anvil: 5.5 ·104
Al ti
tude
(km
)
20
10
050 250Horizontal distance (km)
177.5 316.2 562.5 1000.0
Aitken mode (6nm<d<30nm)
Concentration (100 cm-3)100.0
0.1 1.0 10.0 100.0 1000.0
Acc. mode aerosol (d>30nm)
20
10
0Al ti
tude
(km
)
50 250Horizontal distance (km)
Concentration (cm-3)
Current Aerosol Dynamic Models
1. Continuous size distribution models:Solving the aerosol general dynamic
equation in continuous form.
2. Sectional models:10+ size sections, fixed or moving; mass
only or mass and number; inherent internal mixture structure.
3. Moment models:Using prognostic moments to close the size
distribution with or without a prescribed function; chemistry-based multiple mode structure;single-moment = mass only external mixture model.
Accuracy in Representation
ComputationalAffordability
Current selection
(Wilson et al., 2001; Ekman et al., 2004)
SO4 (g) SO4 nuc
SO4 ait
SO4 acc
BC/OC/SO4
mixedBC
pure
nucleation
condensationemissions
dry deposition
coagulation
nucleation and impact scavenging‘growth’
The size- and chemical-resolving aerosol modal model
Work in progress: ternary nucleationAdditions: pure OC mode; nitrate to mixed modePrescribed: climatological dust and sea salt
Sub-grid processesin most currentglobal models
Scales of Key Chemical Species in Troposphere
102 reactions and 40 prognostic speciesare normally used to describe the NOx-HOx-VOC-O3 system
Local processes
Sec.-Min.
VOCs
NOx
AerosolTrop O3
HOx
CO
< 100 101 102 103 104 ~106
CH410 Yrs
Week
Day
Hour
Month
Tro
po
sp
her
ic L
ife
tim
e
Corresponding Spatial Scale (km)
(Courtesy of Andreas Richter)
Inhomogeneous Distribution of Key Precursors:(Do we need to apply complicated chemistry everywhere?)
Initial VOC (ppmC)
0.0 0.5 1.0 1.5 2.0
Init
ial N
Ox
(p
pm
)
0.00
0.05
0.10
0.15
0.20
0.25
20
40
60
80
100
120
140
160
180
200
Nonlinearity in Fast Chemistry:O3 Mole Fraction (ppb) Derived Using CB4 Mechanism
Coupling the Urban and Global Chemistry Models:An alternative solution
(Mayer et al., 2000)
Emission Preprocessor
Urban Air Pollution Model
Grid Model:Background
Chemistry
ParameterizedUrban Model:Fast Urban Chemistry
RuralEmissions
UrbanEmissions
Grid Concentrations ofChemical Species
Total Emissions
Grid-modelPredictions
Urban-modelPredictions
Daily Predictions of the Models Preprocessors
Modeled troposphericmean properties of
key species from runsincluding and excludingthe Urban Meta Model
MIT IGSM120-Year Runs
The Interactive Aerosol-Chemistry-Climate ModelA collaborative effort of MIT and NCAR scientists
References: Wang (2004); Wang et al. (1998); Mayer et al. (2000); Kiehl et al. (1998); Barth et al. (2000); Rasch et al. (2000); and Kiehl et al. (2000)
AGCM:NCAR CAM + CLM
Atmospheric circulation and stateClouds and precipitation
Radiation
Atmospheric Chemistry andAerosol Model:
25 Chemical species5 or 6 Aerosol modes
Advection, convection, and mixingGaseous and aqueous reactions
Wet and dry deposition
Urban Air Pollution Model
Concentrations Concentrations of Chemicalsof Chemicals& Aerosols& Aerosols
Winds, T, HWinds, T, H22O,O,
Precipitation Precipitation & Radiative & Radiative
FluxesFluxes
OGCM or SST Data
A-O ExchangesA-O Exchanges
MIT EPPA
EmissionsEmissions
Note: This is an alternative effort to other colleagues’ similar works
Selected Issues of Interest for 3D Interactive ModelingSelected Issues of Interest for 3D Interactive Modeling
• Aerosol-cloud interaction and hydrological cycle
• Urban O3 production and export on tropospheric chemistry
• Estimate of future environmental evolution with climate change
Acknowledgements
NSF, NASA, Ford-MIT Alliance, US EPA, and MIT Joint Program on the Science and Policy of Global Change
Model Evaluation
• Ground: AGAGE, NOAA CMDL, ARONET, etc.
• Satellite: MODIS, POLDER, GOME, MOPITT, TES, etc.
• Others: Field experiment data, NCAR aerosol climatology, etc.
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