Air pollution control has become an essential part of operations for many industries particularly the chemical process industries. In developed countries, air quality problems are attributable to the by‐products of combustion processes used in the private and public transportation sectors of the economy, as well.
Frequently; however, planners fail to acknowledge that control systems themselves are industrial processes that consume energy and can emit significant amounts of pollutants into the atmosphere. Regulators have tended to pursue the control of each target pollutant independently with little consideration of secondary pollutants.
In the United States, for example, regulation of air pollution started with the largest sources because they had the most potential for immediate environmental improvement and because the major corporations responsible for these sources could reasonably be asked to assimilate the costs of added controls. The next regulatory phase saw a progressive tightening of standards and application of limits to more and smaller sources, with priority pollutants targeted as separate and distinct entities to be controlled.
Air Emission Estimates
It is critical for a facility to make realistic estimates of the emissions it produces, which will help in determining compliance, predicting potential public exposure and health impacts and designing effective air pollution control equipment or strategies (Karell 2017).
Emission Factors
Valid emission factors for each source of pollution are the key to the emission inventory. It is not uncommon to find emission factors differing by 50%, depending on the researcher, variables at the time of emission measurement, etc. Since it is possible to reduce the estimating errors in the inventory to ±10% by proper statistical sampling techniques, an emission factor error of 50% can be overwhelming. It must also be realized that an uncontrolled source will emit at least 10 times the amount of pollutants released from one operating properly with air pollution control equipment installed.
Actual emission data are available from many handbooks, government publications, and literature searches of appropriate research papers and journals. It is always wise to verify the data, if possible, as to the validity of the source and the reasonableness of the final number. Some emission factors, which have been in use for years, were only rough estimates proposed by someone years ago to establish the order of magnitude of the particular source.
Emission factors must be also critically examined to determine the tests from which they were obtained. For example, carbon monoxide from an automobile will vary with the load, engine speed, displacement, ambient temperature, coolant temperature, ignition timing, carburetor adjustment, engine condition, etc. However, in order to evaluate the overall emission of carbon monoxide to an area, we must settle on an average value that we can multiply by the number of cars, or kilometers driven per year, to determine the total carbon monoxide released to the area.
Published emission factors are available in the literature for many process situations and types of equipment. These are often calculated and published by the USEPA and other agencies, equipment vendors, and trade associations. Many of these emission factors are published in normalized terms, such as pounds of contaminant per 1000 gal of certain fuel combusted, pounds per kilowatt of electricity produced, etc. Manufacturers often provide an emission factor as a guarantee, which enables the user to estimate the emissions from the equipment and obtain a permit for the unit.
Compilation of air pollutant emissions factors (AP‐42) (Table C.1) and emission inventories have long been fundamental tools for air quality management (USEPA 1995). Emission estimates are important for developing emission control strategies, determining applicability of permitting and control programs, ascertaining the effects of sources and appropriate mitigation strategies, plus a number of other related applications by an array of users including federal, state, local agencies, consultants, and industry. Data from source‐specific emission tests or continuous emission monitors are usually preferred for estimating a source’s emissions because those data provide the best representation of the tested source’s emissions. However, test data from individual sources are not always available and, even then, they may not reflect the variability of actual emissions over time. Thus, emission factors are frequently the best or only method available for estimating emissions, in spite of their limitations.
The passage of the Clean Air Act Amendments of 1990 (CAAA) and the Emergency Planning and Community Right‐to‐Know Act (EPCRA) of 1986 has increased the need for both criteria and HAP emission factors and inventories. The Emission Factor and Inventory Group (EFIG), in the USEPA’s Office of Air Quality Planning and Standards, develops and maintains emission estimating tools to support the many activities mentioned above. The AP‐42 series is the principal means by which EFIG can document its emission factors. These factors are cited in numerous other EPA publications and electronic data bases, but without the process details and supporting reference material provided in AP‐42.
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