Page 122 - Fundamentals of Air Pollution

92 6. Sources of Air Pollution

Fig. 6-12. Emissions from uncontrolled automobiles (and those meeting U.S. Environmen-
tal Protection Agency standards) in grams per kilometer.

V. EMISSION INVENTORY

An emission inventory is a list of the amount of pollutants from all sources en-
tering the air in a given time period. The boundaries of the area are fixed (8).
The tables of emission inventory are very useful to control agencies as
well as planning and zoning agencies. They can point out the major sources
whose control can lead to a considerable reduction of pollution in the area.
They can be used with appropriate mathematical models to determine the
degree of overall control necessary to meet ambient air quality standards.
They can be used to indicate the type of sampling network and the locations
of individual sampling stations if the areas chosen are small enough. For
example, if an area uses very small amounts of sulfur-bearing fuels, estab-
lishing an extensive SO 2 monitoring network in the area would not be an
optimum use of public funds. Emission inventories can be used for publicity
and political purposes: "If natural gas cannot meet the demands of our
area, we will have to burn more high-sulfur fuel, and the SO 2 emissions
will increase by 8 tons per year."
The method used to develop the emission inventory does have some
elements of error, but the other two alternatives are expensive and subject
to their own errors. The first alternative would be to monitor continually
every major source in the area. The second method would be to monitor
continually the pollutants in the ambient air at many points and apply
appropriate diffusion equations to calculate the emissions. In practice, the
most informative system would be a combination of all three, knowledge-
ably applied.
The U.S. Clean Air Act Amendments of 1990 (10) strengthened the emis-
sion inventory requirements for plans and permits in nonattainment areas.
The amendments state:
"INVENTORY.—Such plan provisions shall include a comprehensive, accurate,
current inventory of actual emissions from all sources of the relevant pollutant or