Section 7.2.3 of the Guideline on Air Quality Models (EPA, 2005b) provides the basis for

determining the urban/rural status of a source. For most applications the Land Use Procedure

described in Section 7.2.3(c) is sufficient for determining the urban/rural status. However, there

may be sources located within an urban area, but located close enough to a body of water or to

other non-urban land use categories to result in a predominately rural land use classification

within 3 kilometers of the source following that procedure. Users are therefore cautioned against

applying the Land Use Procedure on a source-by-source basis, but should also consider the

potential for urban heat island influences across the full modeling domain. Furthermore, Section

7.2.3(f) of Appendix W recommends modeling all sources within an urban complex using the

urban option even if some sources may be defined as rural based on the procedures outlined in

Section 7.2.3. Such an approach is consistent with the fact that the urban heat island is not a

localized effect, but is more regional in character.

Another aspect of the urban/rural determination that may require special consideration on a caseby-

case basis relates to tall stacks located within or adjacent to small to moderate size urban

areas. In such cases, the stack height, or effective plume height for very buoyant plumes, may

extend above the urban boundary layer height. Application of the urban option in AERMOD for

these types of sources may artificially limit the plume height. Therefore, use of the urban option

may not be appropriate for these sources, since the actual plume is likely to be transported over

the urban boundary layer. A proper determination of whether these sources should be modeled

separately without the urban option will depend on a comparison of the stack height or effective

plume height with the urban boundary layer height. The urban boundary layer height, ziuc, can be

calculated from the population input on the URBANOPT keyword, P, based on Equation 104 of

the AERMOD formulation document (Cimorelli, et al., 2004):

 

 

n201 - n202 - n203 - n204 - n205 - n206 - n207 - n208 - n209 - n210 - n211 - n212 - n213 - n214 - n215 - n216 - n217 - n218 - n219 - n220 - n221 - n222 - n223 - n224 - n225 - n226 - n227 - n228 - n229 - n230 - n231 - n232 - n233 - n234 - n235 - n236 - n237 - n238 - n239 - n240 - n241 - n242 - n243 - n244 - n245 - n246 - n247 - n248 - n249 - n250

 

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