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Chien Wang

Linking Anthropogenic Aerosols, Urban Air Pollution and Tropospheric Chemistry to Climate ( actually, to CAM/CCSM ). Current and Future Researches. Chien Wang. Massachusetts Institute of Technology. Why do we need an interactive model.

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Chien Wang

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  1. Linking Anthropogenic Aerosols, Urban Air Pollution and Tropospheric Chemistry to Climate (actually, to CAM/CCSM) Current and Future Researches Chien Wang Massachusetts Institute of Technology

  2. Why do we need an interactive model Impacts of Tropospheric Chemistry and Aerosols on Climatic and 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 and Aerosols • Temperature, UV fluxes, and H2O(g) on reaction rates • Cloud and precipitation processing of gases and aerosols • Clouds on aerosols’ effective climate impacts 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)

  3. JJA DJF 0 -1000 -500 500 1000 Importance of Aerosols’ Chemical Compositions: BC Caused Changes in Convective Precipitation Rate (Using the last 20-year means of two 60-year runs coupled with SOM; Wang, 2004) (mm/yr/grid)

  4. Importance of Aerosols’ Number Concentration: Results from Thirty 3-D cloud-resolving model runs (Wang, 2004a&b) Maximum Coverage of Cloud vs.Initial CCN Concentration Total Precipitation vs.Initial CCN Concentration

  5. Aitken mode (6nm<d<30nm) 20 Altitude (km) 10 0 50 250 Horizontal distance (km) 100.0 177.5 316.2 562.5 1000.0 Concentration (100 cm-3) Acc. mode aerosol (d>30nm) 20 Altitude (km) 10 0 50 250 Horizontal distance (km) 0.1 1.0 10.0 100.0 1000.0 Concentration (cm-3) 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

  6. Current selection 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. Computational Affordability Accuracy in Representation

  7. BC pure BC/OC/SO4 mixed SO4 acc condensation emissions dry deposition SO4 ait coagulation nucleation and impact scavenging ‘growth’ SO4 nuc SO4 (g) nucleation The size- and chemical-resolving aerosol modal model Work in progress: ternary nucleation Additions: pure OC mode; nitrate to mixed mode Prescribed: climatological dust and sea salt (Wilson et al., 2001; Ekman et al., 2004)

  8. CH4 10 Yrs CO Month Sub-grid processes in most current global models Aerosol Trop O3 Week Tropospheric Lifetime NOx Day 102 reactions and  40 prognostic species are normally used to describe the NOx-HOx-VOC-O3 system VOCs Hour HOx Sec.-Min. < 100 101 102 103 104 ~106 Local processes Corresponding Spatial Scale (km) Scales of Key Chemical Species in Troposphere

  9. Inhomogeneous Distribution of Key Precursors: (Do we need to apply complicated chemistry everywhere?) (Courtesy of Andreas Richter)

  10. Nonlinearity in Fast Chemistry: O3 Mole Fraction (ppb) Derived Using CB4 Mechanism

  11. Daily Predictions of the Models Preprocessors Grid Concentrations of Chemical Species Grid-model Predictions Urban-model Predictions Grid Model: Background Chemistry Parameterized Urban Model: Fast Urban Chemistry Urban Air Pollution Model Rural Emissions Urban Emissions Total Emissions Emission Preprocessor Coupling the Urban and Global Chemistry Models: An alternative solution (Mayer et al., 2000)

  12. Modeled tropospheric mean properties of key species from runs including and excluding the Urban Meta Model MIT IGSM 120-Year Runs

  13. Atmospheric Chemistry and Aerosol Model: 25 Chemical species 5 or 6 Aerosol modes Advection, convection, and mixing Gaseous and aqueous reactions Wet and dry deposition Concentrations of Chemicals & Aerosols AGCM: NCAR CAM + CLM Atmospheric circulation and state Clouds and precipitation Radiation Winds, T, H2O, Precipitation & Radiative Fluxes OGCM or SSTData MIT EPPA Urban Air Pollution Model Emissions A-O Exchanges The Interactive Aerosol-Chemistry-Climate Model A collaborative effort of MIT and NCAR scientists Note: This is an alternative effort to other colleagues’ similar works 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)

  14. Selected Issues of Interest for 3D Interactive Modeling Model Evaluation • Ground: AGAGE, NOAA CMDL, ARONET, etc. • Satellite: MODIS, POLDER, GOME, MOPITT, TES, etc. • Others: Field experiment data, NCAR aerosol climatology, etc. • 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

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