multiplication operations. The general procedures for

modeling of emissions with SMOKE are described briefly

below, followed by more specific procedures associated

with each emission source type.

4.1 Emission Inventories

Historically, many emission inventories have been compiled

and used for the purpose of regulatory or scientific

assessment of emissions, including spatial and temporal

patterns and trends. Emission inventory data are available

from various sources, often from State and local air

pollution control agencies. The inventories commonly

include area and point source data, and aggregated estimates

of mobile source emissions. The EPA compiles the data into

national annual emission inventories for the United States.

The spatial extent of an inventory may vary from plantspecific

emission data to data for an entire county or more.


4.2 Spatial Allocation of Emission Data

Emission inventory data must be spatially allocated to the

modeling grid from the geographic units in which they are

available. In the United States this usually means allocating

data from the county level to the user-defined grid cells

proportionately to the area of the geographic unit within

each cell. It is possible to substantially improve on the

representativeness of spatial assignments of emission data

by overlaying spatial surrogate data appropriate to the

location of different types of emission sources. For

example, population census tracts and road network location

data may be overlain on county and grid maps to weigh the

fractions of emissions attributable to source category codes

representing activities proportional to population density and

motor vehicles, respectively. The surrogate data currently

used include combinations of population and housing census

data, political boundaries, water boundaries, road networks,

ports, airports, railroads, and detailed land use data. Current

spatial surrogate data are available from EPA at



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