The first method of urban determination is a land use method (Appendix W, Section

38 7.2.3c). In the land use method, the user analyzes the land use within a 3 km radius of the source

39 using the meteorological land use scheme described by Auer (1978). Using this methodology, a

40 source is considered urban if the land use types I1 (heavy industrial), I2 (light-moderate

41 industrial), C1 (commercial), R2 (common residential), and R3 (compact residential) are 50

42 percent or more of the area within the 3 km radius circle. Otherwise, the source is considered a

43 rural source. The second method uses population density and is described in Section 7.2.3d of

44 Appendix W. As with the land use method, a circle of 3 km radius is used. If the population

45 density within the circle is greater than 750 people/km2, then the source is considered urban.

46 Otherwise, the source is modeled as a rural source. Of the two methods, the land use method is

Public Review Draft 03/04/2013


considered more definitive 1 (Section 7.2.3e, Appendix W).

Caution should be exercised with either classification method. As stated in Section 5.1 of

3 the AIG (U.S. EPA, 2009), when using the land use method, a source may be in an urban area

4 but located close enough to a body of water or other non-urban land use category to result in an

5 erroneous rural classification for the source. The AIG in Section 5.1 cautions users against using

6 the land use scheme on a source by source basis, but advises considering the potential for urban

7 heat island influences across the full modeling domain. When using the population density

8 method, Section 7.2.3e of Appendix W states, “Population density should be used with caution

9 and should not be applied to highly industrialized areas where the population density may be low

10 and thus a rural classification would be indicated, but the area is sufficiently built-up so that the

11 urban land use criteria would be satisfied...” With either method, Section 7.2.3(f) of Appendix

12 W recommends modeling all sources within an urban complex as urban, even if some sources

13 within the complex would be considered rural using either the land use or population density

14 method.




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