2000). Table 13.1 lists several current generation air quality models which have been

used to simulate ambient ozone, PM, and regional haze concentrations. Table 13.2 lists several

air quality models which have been used for various ozone and PM applications over the past

decade, but are not widely used at this time. Table 13.3 lists several current dispersion models

that have used to model primary PM. Table 13.4 lists several receptor models that have been

used to identify sources of PM. The list is not intended to be comprehensive. Exclusion of a

model from the list does not necessarily imply that it cannot be used to support a modeled

attainment demonstration or uniform rate of progress assessment. In the same way, inclusion on

the list does not necessarily imply that a model may be used for a particular application.

States/Tribes should follow the guidance in Sections 13.1 and 13.2 in selecting an air quality

model for a specific application.

14.0 How are the Meteorological Time Periods (Episodes) Selected?

Historically, attainment demonstrations have been based on a limited number of episodes

consisting of several days each. In the past, the number of days modeled has been limited by the

speed of computers and the ability to store the model output files. With the advancement in

computer technology over the past decade, computer speed and storage issues are no longer an

impediment to modeling long time periods. In fact, many groups have recently modeled entire

summers and/or full years for ozone, PM2.5, and regional haze (Baker, 2004a) (U.S. EPA,


Ozone based research has shown that model performance evaluations and the response to

emissions controls need to consider modeling results from relatively long time periods, in

particular, full synoptic cycles or even full ozone seasons (Hogrefe, 2000). In order to examine

the response to ozone control strategies, it may not be necessary to model a full ozone season (or

seasons), but, at a minimum. we recommend modeling “longer” episodes that encompass full

synoptic cycles. Time periods which include a ramp-up to a high ozone period and a ramp-down

to cleaner conditions allow for a more complete evaluation of model performance under a variety

of meteorological conditions.


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