Stationary Source Emissions

Point Sources

Sources identified on an individual facility basis or as a single source are called point sources. Refineries and industrial plants are examples of point sources. The emission characteristics of individual facilities vary widely and each facility is examined individually. The Permit Services Division of the BAAQMD collects and maintains a computer data bank with detailed information on point sources. Almost all facilities emitting greater than 2.5 tons/year of any air pollutant are included. The District data bank contains information for about 4,000 facilities. Data on the activity, seasonal variations, and hours of operation are collected from each facility. Parameters which affect the quantity of emissions are updated regularly. Emissions are calculated using detailed data for each of the facilities by various processes. The emissions from combustion and other general processes are computed using generalized or specific emission factors. These factors are periodically reviewed and updated.

Area Sources

Stationary sources not identified individually are called area sources. This term is sometimes extended to cover groups of numerous small point sources, such as dry cleaners or gas stations. Area sources also include the diverse, unpermitted small sources which individually do not emit significant amounts of pollutants but which together make an appreciable contribution to the emission inventory. Examples of area sources are residential heating and use of paints, varnishes, and consumer products. Emissions from these sources are grouped into categories and calculated based on surrogate variables. Information on these surrogates is usually available for the state or by county. Selected surrogates are used to apportion the category emissions into diurnal and spatial patterns. Emissions for some source categories are estimated by the California Air Resources Board (ARB) based on statewide data.

Many area source categories are further classified into subcategories for better emission computation, specification, regulation development, and future-year projections. For example architectural coating categories are subdivided into various types of coatings and varnishes to account for varying solvent content. There are more than 800 different subcategories used in this inventory. Emissions for categories affected by regulations are adjusted to reflect the controls required and the estimated rule effectiveness achieved.