Appendix K



Recommended Improvement

Tennessee Department of Environment and Conservation 

Division of Air Pollution Control 

9th Floor L&C Annex 

401 Church Street 

Nashville, TN 37243

Pre-Hearing Draft

REgional Haze SIP for TN Class I Areas

Appendix K - 1

January 18, 2008
APPENDIX K: RECOMMENDED IMPROVEMENTS 

The Regional Haze Rule requires states to conduct a mid course review in 2012 of 

progress toward reasonable progress goals for 2018. There are several technical 

improvements that are recommended in the emissions inventory and air quality models 

that are used to support regulatory decisions for regional haze. These technical 

improvements are also important for states’ efforts to demonstration attainment of the 

ozone and PM2.5 health standards. 

1) Emissions inventory We need to continue to improve emission inventories for 

regulatory sources, particularly emissions profiles for the composition of PM2.5 

emissions. 

2) Continued improvements are needed in the integrated one-atmosphere air quality 

models that are used to project air quality responses to emissions reductions. The 

interactions among primary and secondary pollutants in the atmosphere affect the 

levels of ozone, PM2.5, and haze in the atmosphere. As our understanding of 

partitioning between gaseous and aerosol phases improves, this understanding needs 

to be reflected in the models. 

 

3) Sulfate performance for the CMAQ regional air quality model is good overall. 

Sulfate deposition is frequently overestimated in the models, particularly in the 

summer months. Overestimation of precipitation volume from convective storms is 

one possible explanation. Improvements in treatment of convective systems in the 

meteorological models would improve projections of pollutant deposition 

concentrations. At the coastal sites, when winds are blowing from the Gulf of 

Mexico or Atlantic Ocean, CMAQ under estimates measured sulfate at the monitors. 

Improvements to emissions inventories for commercial shipping in the Gulf and 

Atlantic were made in 2006; additional refinements to emissions estimates are 

needed. As well CMAQ’s processes should be reviewed for sulfate formation over 

water, including availability of precursor species (hydrogen peroxide and ozone), 

dispersal patterns for moving and fixed SO2 emission sources, and vertical and 

horizontal within clouds over water. The accuracy of meteorological modeling of 

flux at the land-water interface is also an area for additional attention. 

4) Nitrate is overestimated by the CMAQ model in the winter and underestimated in the 

summer, although summer monitored values of nitrate are very low. In the 

southeastern US, nitrate formation is driven largely by level of ammonia available in 

the atmosphere. Our understanding of seasonal variation in ammonia emissions from 

agricultural sources has improved; additional improvements in seasonal allocation of 

annual inventories would improve model estimates of ammonium nitrate formation. 

5) Organic carbon is generally underestimated in the CMAQ in the summer months. 

Improvement in the characterization of primary carbon emissions and partitioning 

between gas and aerosol phase and formation of secondary organic aerosols is 

needed. 

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REgional Haze SIP for TN Class I Areas

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January 18, 2008
6) We need better tools for organic carbon source apportionment. In aged aerosol most 

of primary aerosol has reacted to form some secondary organic aerosol. Improved 

emissions profiles and stable molecular makers for anthropogenic and biogenic 

sources and fossil and modern carbon are critical. 

7) Consistent measurement techniques are needed between rural and urban monitoring 

networks so that concentrations of organic carbon and elemental carbon can be 

compared between sites. 

8) To improve our understanding of the contribution of fire from natural forest fires, 

prescribed burning, land clearing, and agricultural burning, states need to improve 

record keeping. Records should include acres burned, dates, location 

(latitude/longitude), fuel type, and intensity of burn. 

9) Additional improvements to international emissions inventory are needed to improve 

our understanding of boundary conditions for our modeling domain and of the 

contributions from international emissions to pollutant concentrations at the VISTAS 

Class I areas. Currently monthly average inventories are used for non-US sources. 

Even when highly resolved meteorological data are used, these monthly average 

inventories do not reflect the episodic variation in emissions, particularly for fire 

events, that are important at the receptors. In the current modeling we cannot 

distinguish Us from non-US sources of pollutant concentrations at the boundaries of 

the model domain. We need to improve our ability to trace emissions that originate 

within US as they are transported outside our modeling grid so that when they recirculate back into the modeling domain they retain their identify as US emissions 

rather than non-US boundary conditions. 

10) The effect of meteorological model performance on air quality model performance 

needs additional attention. 

11) We need to capture the value of the continuous monitoring by evaluating model for 

the diurnal and spatial patterns seen in the monitored data. 

12) We need to improve confidence in trajectory model for periods greater than 72 hours. 

Currently trajectories of longer duration have such large bands of uncertainty as to 

reduce any conclusions than can be drawn for transport greater than 72 hours. 

Pre-Hearing Draft

REgional Haze SIP for TN Class I Areas

Appendix K - 3

January 18, 2008