Some area/nonpoint and nonroad mobile sources can be assigned point-source locations instead of being assigned spatial surrogates. At this time, the only allowable cases of this are for toxics processing for nonroad mobile and stationary area/nonpoint sources related to airport emissions processes. Smkinven has the capability to make such assignments for any area source from both the toxics and criteria inventories; the example file that comes with SMOKE for this purpose (the ARTOPNT file) only contains entries for the airport emissions processes. Section 4.2, “Test case descriptions” provides more information about the example ARTOPNT file provided with SMOKE.

Because airport location data are readily available, this feature gives users the ability to model airport-related area-source emissions at airport locations, as opposed to spatially allocating them to grid cells using spatial surrogates. Although spatial surrogates could be (and have been) developed to reproduce the same or similar results as the point-source assignments for models such as CMAQ, other models that SMOKE may eventually support (namely ISCST3) require that point-source inputs include the location coordinates. The area-to-point assignment feature in SMOKE will support such a need. Note that for large airports and a small grid, one may want to have the airport emissions gridded using surrogate data since the airport can be large enough to encompass multiple grid cells. Thus, the user should decide whether and when to use this area-to-point feature as opposed to gridding using an airport surrogate.

In SMOKE version 1.5 and higher, SMOKE can assign an area source to one or more locations in a county. For example, when multiple airports are in a county, SMOKE adds sources to the inventory and splits the county-total emissions among the locations based on a factor provided in the ARTOPNT file. All sources remain with the area-source inventory in which they started; they are not moved to a point-source inventory. Any area sources that are assigned point locations are spatially allocated using those locations, as described in Section 2.12, “Spatial processing”. Sources that are not assigned point-source locations are allocated in the standard way using spatial surrogates.