APPENDIX G

Evaluation of the 2002 GEOS-C HEM Global Chemistry Model Used for Boundary Conditions in the VISTAS Regional Haze ModelingG-2 

### Application of GEOS CHEM for 2002 Boundary Conditions for CMAQ Modeling of the VISTAS Region

Ivar Tombach

5 October 2007

CMAQ modeling of regional haze in the VISTAS region for 2002 and 2018 was carried out on a grid of 12x12 km cells that covers the VISTAS states (AL, GA, FL, MS, SC, NC, TN, KY, VA, WV) and states adjacent to them. This grid is nested within a larger national CMAQ modeling grid of 36x36 km grid cells that covers the con tinental United States, portions of Canada and Mexico, and portions of the Atlantic and Pa cific Oceans along the east and west coasts. Transport of pollution from the national domain in to the VISTAS modeli ng domain is reflected in hourly-varying boundary conditions around the VI STAS domain, which are derived from the CMAQ simulations in the 36 km national domain. The national domain incorporates emissions from northern Mexico and southern Canada, and th erefore explicitly calc ulates the effects of
these international emissions on concentrations at the boundaries of the VISTAS modeling
domain.

Effects of emissions from more distant source s that are outside of the 36 km national domain were estimated using outputs from a global air pollution model. The Big Bend Regional Aerosol and Visibility Observational (BRAVO) study had found that the performa nce of national-scale modeling was enhanced by using monthly averages of outputs from a global air pollution model, GOCART, to generate SO 2 and sulfate boundary conditions for its 36 km national modeling grid (Schichtel, et al., 2005), instead of using the EPA default concentrations that are normally used. VISTAS elected to use a similar approach, us ing the outputs of th e GEOS-CHEM global air pollution model, which also contains a detailed representation of ozone-NO
x -VOC-PM chemistry.

Under EPRI sponsorship, Harvard University ha d already used the GEOS-CHEM model, with

2 ° x2.5 ° horizontal resolution, to estimate natura l conditions and transboundary influences on elemental and organic carbon aeroso ls in the United States in 1998 (Park et al., 2003). After some emission inventory and model improvements, similar information was developed for
sulfate and nitrate aerosols in 2001 (Park et al., 2004).

Under contract to VISTAS (which was acting on behalf of all the RPOs), Harvard then simulated global air pollution for the year 2002 (the VISTAS modeling year) with 4 ° x5 ° horizontal resolution and 3-hour temporal resolution (Jacob, 2005). The coarser grid scale was considered sufficient to provide boundary conditions outside of North America, largely over the oceans. Although the VISTAS simulation was generally si milar to the 2001 EPRI simulation mentioned above, the VISTAS modeling incorporated the fo llowing substantive changes in addition to the change in grid scale: (1) use of U.S. anthr opogenic emissions from the EPA NEI 1999 inventory, except for ammonia; (2) use of forest fire info rmation specific to 2002; (3) inclusion of the secondary organic aerosol (SOA) formation m echanism from Chung and Seinfeld (2002); and (4) inclusion of prototype soil dust and sea sa lt simulations. An additional model improvement, which has since been implemented in the standa rd version of GEOS-CHEM, was the application of surface emissions and dry deposition to the en tire mixed layer column diagnosed by GEOSG-3 (the Global Earth Observation System of NASA) rather than to just the surface layer of the model. Details of the emissions, meteorology, model configuration, an d model performance
evaluation for the VISTAS simulations are de scribed in the report to VISTAS (Jacob, 2005).

For North America, the VISTAS GEOS-CHEM m odeling used monthly-av erage emissions, so
the model results do not reflect diurnal or weekda y-weekend variability in emissions, and also diminish the impacts of episodic emissions, such as the July 2002 wildfire in Ontario, Canada.
The Mexican emissions were from the inve ntory of the BRAVO Study, while Canadian emissions for the year 2000 were used. Emissions from Caribbean islands were not included, which could impact model estimates at the Everglades.

The surface meteorological data inputs to GEOS-CHEM had 3-hr temporal resolution and the upper air meteorological inputs had 6-hr resolution, with a horizontal resolution of 1 ° x1 ° or better and 48 layers vertically.

The output of the GEOS-CHEM mode ling, as delivered to VISTAS, contained concentrations of all visibility-related components of particulate matte r with 3-hr tempor al resolution and 4 ° x5 ° horizontal resolution over multiple layers of the atmosphere.

Even though the coarse spatial resolution degr aded the performance of the model over North America, relative to results from prior m odeling for other years using finer grids, the concentrations simulated by GEOS-CHEM maintain ed the synoptic-scale structure and did not
have a continental-scale bias. At a finer scale, the concentrations simulated by GEOS-CHEM for the surface layer in 2002 were generally within a factor of two of regional-averages (~500 km scale) of measurements of the various chemical components of particulat e matter in the United States and, except for organic carbon, satisfactorily simulated the seasonal variability in the
observations.

In the meantime, Harvard University had also carried out new finer-grid simulations for 2001 for EPRI, using a 1 ° x1 ° grid over North America, nested in a coarser grid that covered the globe.
The final version of these simulations included modifications to the modeling grid to improve
delineation between domestic US emissions a nd those of foreign sources at the national boundaries, and revision (reduction) of the Cana dian and Mexican sulfur emissions. These

GEOS-CHEM 1 ° x1 ° grid scale simulations for 2001 and th eir results are desc ribed in the paper by Park et al. (2006). Over a ppropriate geographic and temporal scales, the results of these
simulations for 2001were similar to those of the 2002 VISTAS simulations, which gave
confidence in the VISTAS GEOS-CHEM results.

The concentration fields that resulted from the GEOS-CHEM simulations were not directly usable as boundary conditions for the 36 km grid scale CMAQ simulations. GEOS-CHEM and CMAQ use different horizontal and vertical grid scales and diffe rent map projections, and have
different labels for chemical constituents . The GEOS-CHEM outputs were processed by Dr. Daewon Byun at the University of Houston to adjust for these discrepancies and to develop boundary conditions for the 36 km CMAQ modeli ng. Since the CMAQ modeling has temporal resolution of one hour, the boundary conditions were given for every hour. However, since the GEOS-CHEM outputs had 3-hr resolution, the hour ly boundary conditions were the same for three consecutive hours. An example of the re sulting boundary conditions for sulfate at the surface is shown in Figure G-1. As indicated by the colors along the boundary of the modelingG-4 domain, GEOS-CHEM projects hi gher sulfate values for th e southern boundary, indicating emissions from Mexico, and the eastern boundary, i ndicating recirculation of emissions from the
eastern US.



# Average Sulfate Boundary Conditions GEOS-CHEM for July 1, 2001

Figure G-1. GEOS-CHEM projections of sulfate boundary conditions for the national CMAQ modeling grid on July 1, 2001.G-5 Model performance for the 2002 4x4 degree annual GEOS-CHEM run was compared to
observations at 145 IMPROVE sites and CASTNET sites across the continental US. Example plots from the model performance evaluation are illustrated in Fi gures G-2 through G-9. Additional information is provided in th e final GEOS-CHEM report (Jacobs, 2005). Performance at the boundaries is driven by accu racy of international emission estimates; performance at US continental monitors is driv en by US emissions. Given the large grid size, projections are approximations th at show the correct order magnitude. Performance for 2002 boundary conditions is acceptable compared to observations and an improvement over the CMAQ default single annual value for all boundaries. Sulfate pr ojections reproduce observed values fairly well, particularly for boundary cond itions. Sulfate is slightly over predicted for winter months. Summer sulfate levels are under pr edicted, particularly on high sulfate days, but mean fraction bias for monthly average sulfate is within performance criteria set for CMAQ (+/- 30%).G-6 Figure G-2. GEOS-CHEM 2002 SO4 annual performance compared to IMPROVE (145 sites) and CASTNET monitoring networks.G-7 Figure G-3. GEOS-CHEM 2002 Monthly SO4 Performance compared to 145 IMPROVE sites in the continental US.

Figure G-4. GEOS-CHEM 2002 Monthly SO4 Performance compared to 145 IMPROVE sites in the continental US. GEOS-CHEM nitrate performance is acceptable for boundary conditions. Nitrate is over predicted at some sites on some winter days; over all nitrate is under predic ted in all months, and particularly in summer months. Since summer nitrate values are gene rally low, this under prediction does not affect overall model performance for CMAQ. 

## Monthly Average Sulfate

0 2 4 6 8 10 12 14

0 2 4 6 8 10 12 14 

## IMPROVE ( μ g/m 3 

## )GEOS-CHEM (μg/m3) January
February

March
April
May

June
July
August
September

October

November

Decembe r



## Sulfate Model Performance (IMPROVE)

-40 -30 -20 -10 0 10 20 30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMean Fractional Bias (%)G-8 Figure G-5. GEOS-CHEM 2002 NO3 annual average performance compared to IMPROVE (145 sites) and CASTNET monitoring networks.G-9 Figure G-6. GEOS-CHEM 2002 Monthly NO3 Performance compared to 145 IMPROVE sites in the continental US.

Figure G-7. GEOS-CHEM 2002 Monthly NO3 Performance compared to 145 IMPROVE sites in the continental US. 

## Monthly Average Nitrate

0 1 2 3 4 5 6 7 8

012345678 

### IMPROVE ( μ g/m 3 

### )GEOS-CHEM (μg/m3) January
February

March
April
May

June
July
August
September

October

November

Decembe r



## Nitrate Model Performance (IMPROVE)

-180 -160 -140 -120 -100

-80 -60 -40 -20 0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMean Fractional Bias (%)G-10 Figure G-8. GEOS-CHEM 2002 Organic Matter Carbon (OMC) annual average performance compared to IMPROVE (145 sites) and CASTNET monitoring networks.

Model performance for organic matter carbon (OMC ) and elemental carbon (EC) are acceptable.
Performance at the boundaries is driven by quality of the fi re inventory for international
emissions. While a new biomass burning inventory was de veloped as part of this study, monthly average fire emissions do not accurately ca pture the impacts from episodic fires.G-11 Figure G-9. GEOS-CHEM 2002 Elemental Carbon annual average performance compared to IMPROVE (145 sites) and CASTNET monitoring networks.

GEOS-CHEM 3-hr average outputs were used as inputs to CMAQ modeling for 2002 and 2018. Since VISTAS did not have information to proj ect future changes in international emissions, VISTAS used the same boundary conditions in 2018 as developed for 2002.

References

Chung, S. H. and Seinfeld, J.H. (2002), Global di stribution and climate fo rcing of carbonaceous aerosols, Journal of Geophysical Research, Vol. 107 (D19), 4407, doi:10.1029/2001JD001397.

Jacob, D.J. (2005), Documenta tion and Evaluation of the GEOS-CHEM Simulation for 2002 Provided to the VISTAS Group. Final re port, Harvard University. June 24.

Park. R.J., Jacob, D.J., Chin, M., and Marti n, R.V. (2003). Sources of carbonaceous aerosols over the United States and implications for natural visibility. Journal of Geophysical Research, Vol. 108 (D12), 4355, doi:10.1029/2002JD003190.G-12 Park. R.J., Jacob, D.J., Field, B.D., Yantos ca, R.M., and Chin, M. (2004). Natural and transboundary pollution influences on sulfate-nitrate-ammonium aerosols in the United States: Implications for policy. Journal of Geophysical Research, Vol. 109, D15204,
doi:10.1029/2003JD004473.

Park. R.J., Jacob, D.J., Kumar, N ., and Yantosca, R.M. (2006). Regi onal visibility statistics in
the United States: Natural a nd transboundary pollution influen ces, and implications for the Regional Haze Rule. Atmospheric Environment, Vol. 40, pp. 5405-5423.

Schichtel, B.A., Gebhart, K.A., Malm, W.C., Barn a, M.G., Pitchford, M.L., Knipping, E.M., and Tombach, I.H. (2005). Reconciliation and Interp retation of Big Bend National Park Sulfur Source Apportionment: Results from the Big Bend Regional Aerosol and Visibility Observational Study – Part I. Journal of the Air & Waste Management Assoc. Vol. 55, pp. 1709-
1725.