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.