Appendix K 

Recommended Improvements 
 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 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. 

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. 
 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 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 

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) 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.