Appendix K 

Recommended Improvements 
Appendix K - 1
Appendix K - 2

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 Continued improvements in emission inventories for regulatory sources, 

particularly emissions profiles for the composition of PM2.5 emissions is necessary. 

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 understanding of partitioning between gaseous and aerosol 

phases improves, models reflecting this understanding need to be developed. 

 

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. Current 

understanding of seasonal variation in ammonia emissions from agricultural sources has 

improved; additional improvements in seasonal allocation of annual inventories would 

further 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. 

6) Better tools for organic carbon source apportionment need to be developed. 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. 
Appendix K - 3

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 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 

understanding of boundary conditions for modeling domains 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. States and RPOs need to improve their ability to 

trace emissions that originate within US as they are transported outside modeling grids so 

that when they re-circulate 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) Values of continuous monitoring need to be captured by evaluating model for the diurnal and 

spatial patterns seen in the monitored data. 

12) Confidence in trajectory model for periods greater than 72 hours also needs to be improved. 

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.