# Appendix M

. 2

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

Tennessee Department of Environment and Conservation
Division of Air Pollution Control
9 th 

### Floor L&C Annex
401 Church Street Nashville, TN 37243

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

5 October 2007

CMAQ modeling of regional haze in the VIST AS region for 2002 and 2018 was carried out on a grid of 12x12-km cells that covers the VI STAS 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 th at covers the contin ental United States, portions of Canada and Mexico, and portions of the Atlantic and Pacific Oceans along the east and west coasts. Transport of pollution from the national domain into the VISTAS modeling domain is reflected in hourly-va rying boundary conditions around the VISTAS domain, which are derived from the CMAQ si mulations in the 36-km national domain. The national domain incorporates emissions from northern Mexico and southern Canada, and therefore explicitly calculates the effects of th ese international emissions on concentrations
at the boundaries of the VISTAS modeling domain.

Effects of emissions from more distant sour ces 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 Observ ational (BRAVO) study had found that the performance 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, using the outputs of the GEOS-Chem global air pollution model, which also contains a detailed representation of ozone-NO
x 

### -VOC-PM chemistry.

Under EPRI sponsorship, Harvard University had already used the GEOS-Chem model,
with 2 ° x2.5 ° horizontal resolution, to estimate na tural conditions and transboundary influences on elemental and organic carbon aero sols 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 re solution (Jacob, 2005). The coarser grid scale was considered sufficient to provide boundary co nditions outside of North America, largely over the oceans. Although the VISTAS simula tion was generally similar to the 2001 EPRI simulation mentioned above, the VISTAS modeli ng incorporated the following substantive changes in addition to the cha nge in grid scale: (1) use of U.S. anthropogenic emissions from the EPA NEI 1999 inventory, except for amm onia; (2) use of forest fire information specific to 2002; (3) inclus ion of the secondary organi c aerosol (SOA) formation mechanism from Chung and Seinfeld (2002); an d (4) inclusion of pr ototype soil dust and sea salt simulations. An additional model improvement, which has since been implemented in the standard version of GEOS-Chem, was the application of surface emissions and dry2 deposition to the entire mixed layer colu mn diagnosed by GEOS (the Global Earth Observation System of NASA) rather than to just the surface layer of the model. Details of the emissions, meteorology, model configura tion, and model performance evaluation for
the VISTAS simulations are described in the report to VISTAS (Jacob, 2005).

For North America, the VISTAS GEOS-Chem modeling used monthl y-average emissions,
so the model results do not reflect diurnal or weekday-weekend vari ability in emissions, and also diminish the impacts of episodic emi ssions, such as the July 2002 wildfire in Ontario, Canada. The Mexican emissions were from the inventory of the BRAVO Study, while Canadian emissions for the year 2000 we re used. Emissions from Caribbean islands were not included, which could impact model estimates at the Everglades.

The surface meteorological data inputs to GE OS-Chem had 3-hr temporal resolution and the upper air meteorological i nputs had 6-hr reso lution, with a horizon tal resolution of

1 ° x1 ° or better and 48 layers vertically.

The output of the GEOS-Chem modeling, as delivered to VISTAS, contained concentrations of all visibility-related compone nts of particulate matter with 3-hr temporal
resolution and 4 ° x5 ° horizontal resolution over multiple layers of the atmosphere.

Even though the coarse spatial resolution de graded the performance of the model over North America, relative to results from prior modeling for other years using finer grids, the concentrations simulated by GEOS-Chem mainta ined the synoptic-sca le structure and did
not have a continental-scale bias. At a finer scale, the concentrations simulated by GEOSChem for the surface layer in 2002 were genera lly within a factor of two of regionalaverages (~500 km scale) of measurements of the various chemical components of particulate matter in the United States a nd, 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 simula tions included modifications to the modeling grid to improve delineation between domestic US emissions and those of foreign sources at the national boundaries, and revision (reduction) of the Canadian and Mexican sulfur
emissions. These GEOS-Chem 1 ° x1 ° grid scale simulations for 2001 and their results are described in the paper by Park et al. (2006) . Over appropriate ge ographic 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 horizonta l and vertical grid scales and different map projections,
and have different labels for chemical constituents. The GEOS-Chem outputs were processed by Daewon Byun at the University of Houston to adjust for these discrepancies and to develop boundary conditions for th e 36-km CMAQ modeling. Since the CMAQ modeling has temporal resolution of one hour, the boundary conditions were given for3 every hour. However, since the GEOS-Chem outputs had 3-hr resolution, the hourly boundary conditions were the same for three consecutive hours. An example of the resulting boundary conditions for sulfate at the surface is shown in Figure 1. As indicated by the colors along the boundary of the m odeling domain, GEOS-Chem projects higher sulfate values for the southern boundary, indica ting emissions from Mexico, and the eastern boundary, indicating recirc ulation of emissions from the eastern US.



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

Figure 1. GEOS-CHEM projections of sulf ate boundary conditions for the national CMAQ modeling grid on July 1, 2001

Model performance for the 2002 4x4 degree a nnual GEOS-Chem run was compared to
observations at 145 IMPROVE sites and CASTNET sites across the continental US. Example plots from the model performance ev aluation are illustrated in Figures 2-9. 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 dr iven by US emissions. Given the large grid size, projections are approximations that show the correct order magnitude. Performance for 2002 boundary conditions is acceptable comp ared to observations and an improvement over the CMAQ default single annual value for all boundaries. Sulfate projections reproduce observed values fairly well, par ticularly for boundary conditions. Sulfate is slightly over predicted for winter months. Summer sulfate levels are under predicted, particularly on high sulfate days, but mean fr action bias for monthly average sulfate is within performance criteria set for CMAQ (+/- 30%).

### 4 Figure 2. GEOS-Chem 2002 SO4 annual performa nce compared to IMPROVE (145 sites) and CASTNET monitoring networks.

### 5 Figure 3. GEOS-Chem 2002 Monthly SO4 Perfor mance compared to 145 IMPROVE sites
in the continental US.

Figure 4. GEOS-Chem 2002 Monthly SO4 Perfor mance compared to 145 IMPROVE sites
in the continental US. 

## 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 (%)6 GEOS-Chem nitrate performance is acceptable for boundary conditions. Nitrate is over predicted at some sites on some winter days; ov erall nitrate is under pr edicted in all months, and particularly in summer months. Since summ er nitrate values are generally low, this under prediction does not affect overa ll model performance for CMAQ.

Figure 5. GEOS-Chem 2002 NO3 annual average performance compared to IMPROVE (145 sites) and CASTN ET monitoring networks.7 Figure 6. GEOS-Chem 2002 Monthly NO3 Performance compared to 145 IMPROVE sites
in the continental US.

Figure 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 (%)8 Figure 8. GEOS-Chem 2002 Organic Carbon an nual average performance compared to IMPROVE (145 sites) and CAST NET monitoring networks.

Model performance for organic carbon matte r and elemental carbon are acceptable. Performance at the boundaries is driven by quali ty of the fire inventory for international emissions. While a new biomass burning invent ory was developed as part of this study, monthly average fire emissions do not accurately capture the impacts from episodic fires.9 Figure 9. GEOS-Chem 2002 Elemental Carbon a nnual average performance compared to IMPROVE (145 sites) and CAST NET 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 project future cha nges in international emissions, VISTAS used the same boundary conditions in 2018 as developed for 2002.

References

Chung, S. H. and Seinfeld, J.H. (2002), Gl obal distribution and climate forcing of carbonaceous aerosols, Journal of Geophysical Research, Vol. 107 (D19), 4407,
doi:10.1029/2001JD001397.

Jacob, D.J. (2005), Documentation and Evalua tion of the GEOS-Chem Simulation for 2002 Provided to the VISTAS Group. Final re port, Harvard University. June 24.10 Park. R.J., Jacob, D.J., Chin, M., and Mart in, 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.

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 Yantos ca, R.M. (2006). Regional visibility statistics in the United States: Natural and transboundary pollution influences, and implications for the Regional Haze Rule. Atmospheric Environment, Vol. 40, pp. 5405-5423.

Schichtel, B.A., Gebhart, K.A., Malm, W.C ., Barna, M.G., Pitchford, M.L., Knipping, E.M., and Tombach, I.H. (2005). Reconciliati on and Interpretation 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 & Wa ste Management Assoc. Vol. 55, pp. 1709-1725.