This document discusses atmospheric chemistry models and their use in quantifying atmospheric concentrations and fluxes. Global 3D models divide the atmosphere into grid boxes and use the continuity equation to track species concentrations over time, accounting for transport, chemistry, emissions and deposition. Transport is parameterized using turbulence and convection schemes. Chemistry is solved using operator splitting and implicit methods. Models are evaluated and improved using atmospheric observations from satellites, aircraft and surface sites through data assimilation techniques like inverse modeling. Examples are given of various applications of the GEOS-CHEM global model.

1. ATMOSPHERIC CHEMISTRY MODELS Daniel J. Jacob Harvard University http://www-as.harvard.edu/chemistry/trop

2. OBJECTIVE OF ATMOSPHERIC CHEMISTRY MODELS: QUANTIFY THE CONCENTRATIONS AND FLUXES OF ATMOSPHERIC SPECIES IN TIME AND SPACE Fires Land biosphere Human activity Lightning Ocean physics chemistry biology Volcanoes MEASURES OF ATMOSPHERIC CONCENTRATIONS: Number density n i (x, t ) [molecules cm -3 ] Mixing ratio (mole fraction) C i (x, t ) [mol/mol]

8. TURBULENT COMPONENT DOMINATES VERTICAL FLUX IN LOWER ATMOSPHERE vertical wind w T CO 2 small large Example: CO 2 flux observations at Harvard Forest, Massachusetts

9. THE TRANSPORT OPERATOR: parameterization of convection Convective cloud (0.1-100 km) Model grid scale Model vertical levels updraft entrainment downdraft detrainment Convection is subgrid scale in global models and must be treated as a vertical mass exchange separate from transport by grid-scale winds. Need info on convective mass fluxes from the model meteorological driver.

13. Eulerian research models use assemblages of boxes exchanging mass to resolve spatial structure Lagrangian research models use assemblages of traveling puffs not exchanging mass, and sum over all puff trajectories to resolve spatial structure LAGRANGIAN vs. EULERIAN MODELING APPROACHES n i (x,t o ) n i (x,t o  t 

18. LONG-RANGE TRANSPORT OF POLLUTION: SURFACE OZONE ENHANCEMENTS CAUSED BY ANTHROPOGENIC EMISSIONS FROM DIFFERENT CONTINENTS GEOS-CHEM model, July 1997 North America Europe Asia Li et al. [2001] Li et al. [2002]

19. COLUMN MEASUREMENT OF AN ABSORBING GAS USING SOLAR BACKSCATTER EARTH SURFACE Scattering by Earth surface and by atmosphere ATMOSPHERE absorption wavelength     Slant optical depth Backscattered intensity I B Slant column    

20. AIR MASS FACTOR (AMF) CONVERTS SLANT COLUMN  S TO VERTICAL COLUMN  “ Geometric AMF” (AMF G ) for non-scattering atmosphere: EARTH SURFACE 

21. IN SCATTERING ATMOSPHERE, AMF CALCULATION REQUIRES MODEL INFORMATION ON THE SHAPE OF THE VERTICAL PROFILE: d  (z) I o I B EARTH SURFACE RADIATIVE TRANSFER MODEL Scattering weight ATMOSPHERIC CHEMISTRY MODEL Shape factor z number density n(z) Palmer et al. [2001]

22. ATMOSPHERIC COLUMNS OF NO 2 AND FORMALDEHYDE (HCHO) MEASURED BY SOLAR BACKSCATTER FROM GOME ALLOW MAPPING OF NO x AND HYDROCARBON EMISSIONS Emission NO h  (420 nm)  O 3 , RO 2 NO 2 HNO 3 1 day NITROGEN OXIDES (NO x ) NON-METHANE HYDROCARBONS Emission NMHC OH HCHO h  (340 nm)  hours CO hours BOUNDARY LAYER ~ 2 km Tropospheric NO 2 column ~ E NOx Tropospheric HCHO column ~ E NMHC Deposition GOME SATELLITE INSTRUMENT … but model info is needed for the vertical distributions of NO 2 and HCHO

23. CAN WE USE GOME TO ESTIMATE NO x EMISSIONS? TEST IN U.S. WHERE GOOD A PRIORI EXISTS Comparison of GOME retrieval (July 1996) to GEOS-CHEM model fields using EPA emission inventory for NO x GOME GEOS-CHEM (EPA emissions) BIAS = +3% R = 0.79 Martin et al. [2002]

24. GOME RETRIEVAL OF TROPOSPHERIC NO 2 vs. GEOS-CHEM SIMULATION (July 1996) GEIA emissions scaled to 1996 Martin et al. [2002]

25. FORMALDEHYDE COLUMNS FROM GOME: July 1996 means BIOGENIC ISOPRENE IS THE MAIN SOURCE OF HCHO IN U.S. IN SUMMER Palmer et al. [2001]

26. MAPPING OF ISOPRENE EMISSIONS FOR JULY 1996 BY SCALING OF GOME FORMALDEHYDE COLUMNS [Palmer et al., 2002] GEIA (IGAC inventory) BEIS2 GOME COMPARE TO…

27. PROGRESS IN ATMOSPHERIC CHEMISTRY REQUIRES INTEGRATION OF MEASUREMENTS AND MODELS 3-D CHEMICAL TRACER MODELS QUANTITATIVE PREDICTIONS SATELLITE OBSERVATIONS Global and continuous but few species, low resolution AIRCRAFT OBSERVATIONS High resolution, targeted flights provide critical snapshots for model testing SURFACE OBSERVATIONS high resolution but spatially limited Source/sink inventories Assimilated meteorological data Chemical and aerosol processes