This guidance recommends using regional modeling domains. Regional modeling

applications require coordination, quality assurance and management of data bases covering

large areas of the country. Resources used to run recommended models for generating

meteorological and emissions inputs and the air quality model itself can be substantial.

States/Tribes facing the need to develop an attainment demonstration requiring resource

intensive techniques may wish to consider pooling resources in some manner. Examples might

include delegating responsibilities for certain parts of the analyses to a single State/Tribe which

can “specialize” in that kind of analysis. Another example might be formation of a regional

technical center to perform analyses as directed by its client group of States/Tribes (e.g., multistate

and tribal organizations such as the Regional Planning Organizations (RPO) 10, LADCO,

and the Ozone Transport Commission (OTC)).

Premise 4. High concentrations of ozone, PM2.5 and regional haze often have a common

origin. Ozone formation and formation of secondary particulates result from several common

reactions and reactants. Secondary particulates are a major part of PM2.5. Often similar sources

contribute precursors to both ozone and PM2.5. In some regions of the U.S., high regional ozone

and secondary particulates are observed under common types of meteorological conditions.

Reducing PM2.5 is the principal controllable means for improving regional haze. Reducing PM2.5

precursors can also lead to reductions in ozone. Models intended to address secondary

particulate matter problems need also to be capable of simulating ozone formation and transport.

U.S. EPA policy is to encourage “integration” of programs to reduce ozone, PM2.5 and regional

haze to ensure they do not work at cross purposes and to foster maximum total air quality benefit

for lower costs.


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