5.2.1 Increment and NAAQS Cumulative Long Range Transport


Sources at distances greater than 50 km from a given

receptor should be analyzed with the MESOPUFF-II model, run as

described in Appendix A. This includes using the chemical

transformation and deposition algorithms. Sources within 50 km

of a receptor should be modeled using the appropriate model and

model options, as recommended in the Guideline. The

concentrations from these two analyses should be added on an

hour-by-hour, receptor-by-receptor, and pollutant-by-pollutant


There will be occasions when a source will be both nearer

and farther than 50 km from receptors in an analysis. It is

not intended that such a source be analyzed with both models.

In general, the nearer receptors will yield the controlling

concentrations for that source, therefore, the appropriate

Guideline model should generally be run for all receptors, for

that source. If, however, it is determined that a particular

source, modeled with a steady-state, Gaussian model, is

possibly causing an exceedance at a receptor more than 50 km

from the source, it is obviously appropriate to model its

impacts at that receptor with the long range transport model,

to more accurately estimate its impacts. Again, it is expected

that a fair degree of professional judgement will need to be

exercised in these analyses.

When analyzing impacts in a large Class I area it may be

appropriate to divide the steady-state, Gaussian plume analyses

into several source groups and use meteorological data

appropriate to each source group. For example, if a Class I

area is 150 km long, it is unlikely that sources located at

opposite ends of the area will experience the same meteorology.

Therefore, it may be appropriate to use representative



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