PHASE 1 RECOMMENDATION SUMMARY

Until the Phase 2 work of the IWAQM is complete the IWAQM

recommends the following modeling approach be used under

circumstances which require the analysis of Class I area

impacts for sources more than 50 kilometers and up to several

hundred kilometers away. This recommendation is interim in

that certain technical compromises were made in order to

satisfy the immediate need for a workable modeling approach.

I. LEVEL I ANALYSIS (PLUME MODEL)

A. PSD INCREMENT AND STANDARDS

(1) For conditions other than extended

stagnation or known conditions of pollutant

recirculation, a steady-state, Gaussian

plume model may be used for all sources.

(2) Mass removal model options for either

chemical transformation or deposition

should not be employed.

(3) Where recirculation or stagnation is known

to be important the applicant should use

the Level II analysis only.

(4) If the Level I analysis indicates an

exceedance then a complete Level II

analysis should be performed.

B. VISIBILITY

The applicant should use the same approach as is

described in I.A. with the following additions:

(1) Assume that all of the emitted SO and NO 2 X

has been converted to SO and NO =

4 3

respectively.

(2) The concentrations of SO and NO should =

4 3

then be used in conjunction with the

techniques presented in Appendix B to

estimate impacts on Class I area

visibility.

C. OTHER AQRVs

The applicant should use the same approach as is

described in I.A. with the following additions:

(1) Assume that all of the emitted SO remains 2

as SO and that the NO has been converted 2 X

to HNO . 3

(2) Use appropriate deposition velocities to

estimate the deposition of the pollutants.

(See Inset 2.)

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