Historic PAS Report Series
PAS published its first Information Report in 1949. To celebrate this history, each month we're presenting a new report from the archives.
We hope you enjoy this month's fascinating snapshot of a planning issue of yesteryear.
AMERICAN SOCIETY OF PLANNING OFFICIALS
1313 EAST 60TH STREET — CHICAGO 37 ILLINOIS
|Information Report No. 212||July 1966|
Air Zoning: An Application of Air Resource Management
Prepared by Michael J. Meshenberg
For when in all other places the Aer is most Serene and Pure, it is here Ecclipsed with such a Cloud of Sulphure, as the Sun itself, which gives day to all the World besides, is hardly able to penetrate and impart it here; and the weary Traveller at many Miles distance, sooner smells, than sees the City to which he repairs.
-- Fumifugium: or the Inconvenience of the Aer, and Smoke of London Dissipated.l
In 1955, at the annual meeting of the Air Pollution Control Association, a paper was presented by Francois N. Frenkiel in which the concept of air zoning was described in detail for the first time.2 The concept has since been refined and further developed but it has generally received little attention from planners. It is the intention of this report to correct this oversight by defining air zoning operationally, by describing both its applicability and its limitations, and by placing it in its proper context within an over-all air pollution study and abatement program. It is important to emphasize that air zoning is but one approach to maximizing air purity and that it can only become practical after completion of the series of studies and analyses that are included in air resource management.
The intent of the present report is to emphasize the fact that the air over most of our urban areas is becoming increasingly contaminated and that planners, whose concern is the improvement of the total urban environment, need to direct their talents and energies toward the alleviation of air pollution. It is hoped that this report will help to stimulate that interest.
The present report is in the tradition of the occasional ASPO Planning Advisory Service report which describes a relatively new concept before it is widely accepted and used by many communities. Unlike most PAS reports, it does not give detailed examples of current practice, simply because there is as yet no community where air zoning has been fully applied. The examples mentioned are used to illustrate particular aspects of air zoning; they are not necessarily the "best" approaches. Future research will undoubtedly improve each of them.
Two previous Planning Advisory Service Reports, Air Pollution Control (No. 20, November 1950) and Air Pollution — A Growing Urban Problem (No. 79, October 1955), discussed in detail the types and effects of air pollution and the available methods of control. Although much research has been done since the above reports were written, their general discussion of the problem and the technical controls remains useful. This report will not duplicate the information in either of the previous reports.
A Framework for Air Zoning
The rationale for any pollution abatement program is the prevention of damage. Pollution-produced damage, e.g., the aggravation of some respiratory conditions, irritation of the eyes, destruction of plants, deterioration of paint, soiling of clothing, is the result of a series of steps which compose the problem. These steps, as described by Frenkiel in the paper noted above, are: (1) production of the pollutants, usually a by-product of a combustion or crushing process; (2) emission of the pollutants into the atmosphere; (3) their transfer from the point of emission by the flow of air, and (4) the contact with receptors (e.g., lungs, buildings, vegetation) which are finally damaged (see Figure 1).
Schematic Representation of the Atmospheric Pollution Cycle
SOURCE: Atmospheric Pollution in Growing Communities by Francois N. Frenkiel. The Smithsonian Report for 1956. Washington: Smithsonian Institution, 1957. P. 213.
Technological advances have been made at a rapid rate over the last few decades both in preventing the production of pollutants, particularly by improving the quality of fuel and increasing the efficiency of combustion processes, and in controlling emission by the installation of devices which trap pollutants before they are emitted into the atmosphere. In many cases these methods are extremely effective in reducing the amount of pollution produced and the amount emitted. Unfortunately, however, the most efficient of these source controls — i.e., controls affecting production and emission — often require changes in production methods or the installation of expensive devices. Therefore, unless more economical means are devised to eliminate pollution at its source, or until the problem becomes so acute that the public will demand source controls regardless of cost, it is necessary to investigate all possible means of attacking the problem at the transfer and contact stages. Since source control is primarily an engineering problem with which the planner has only indirect involvement, his talents can best be utilized in locating sources and receptors, determining zones of higher air quality, and setting standards so that the emissions will cause as little damage as possible.
Air Zoning Defined
Air pollution regulations have been in effect in many parts of the country for a number of years. They have usually taken the form of a single set of regulations for an entire air pollution control district — state, city, a county, or, in some cases such as Los Angeles and San Francisco, several counties. Until about six or seven years ago, the regulations were imposed directly on the sources of pollution without specifically determining the goals of the regulations.
Recently, however, the concept of air quality standards has begun to attain widespread acceptance, giving local, metropolitan, or state agencies a more rational basis upon which to establish regulations. Briefly (they will be discussed in detail below), air quality standards are goals determined by a community and definitions of the maximum level of air pollution it wishes to permit. Some states, including New York, California, and Oregon, and metropolitan control districts, such as Los Angeles, San Francisco, and Dade County, Florida, have enacted the standards into law.
Air zoning rests heavily on the determination of air quality standards but carries the concept a step further by establishing different standards for different sections (or zones) within the jurisdiction. For example, a heavily industrialized area would be permitted to maintain a higher level of pollution concentration than would a forest or an agricultural area. Within this framework, then, air zoning can be defined as the establishment of limits on the amount and type of pollution that will be tolerated in the atmosphere of different parts of an area under specified conditions.
The need for air zoning arises out of a conflict of goals. These conflicts relate to the desire for air purity, on one hand, and to the practical necessity of retaining pollution emitters, on the other. Of course, the air we breathe should be clean and healthful. At the same time, most communities, or at least most metropolitan areas, cannot be deprived of such pollution emitters as industry and motor vehicles. If the economics of air pollution source control were such that it was relatively inexpensive to institute effective control devices, the conflict would not exist. At the present time, however, this conflict is evident in virtually every metropolitan area, and until it is resolved air zoning is a reasonable solution.
Air Zoning Contrasted with Land Zoning
Because of the city planner’s familiarity with the concept of zoning as applied to the land, some confusion may arise from the application of the same term to the atmosphere. While there are some basic similarities between the two, their differences may very well be greater. The major reason for the use of the term here is its general acceptance in the literature of the environmental health field.
The common denominator of the concepts of air zoning and land zoning is that a single area of jurisdiction is divided into zones which will be subject to different standards. This division, however, is the only thing that is truly common to both.
The major differences are:
Implementation of Objectives. — Traditional land-use zoning is a set of restrictions on the use of land. These restrictions are based on objectives which are separate from the restrictions and, ideally, taken from a comprehensive plan. The implementation of the objectives takes the form of regulations on the density, bulk, height, and so forth of various land uses.
Air zoning, on the other hand, incorporates both objectives and restrictions and in a sense, therefore, may be compared to both a comprehensive plan and a zoning ordinance. The objectives take the form of air quality standards which differ from area to area within the jurisdiction. The restrictions take the form of allowable emission rates. Because of the complex relationship between each emitter and over-all air quality, it seems difficult to translate air quality objectives into permitted emission rates. However, the engineers tell us that fair and equitable emission controls can in fact be derived from air quality standards for most pollutants.3
Geographical Area. — Because the configuration of the land can be expected to remain stable over an indefinite period, it is possible to draw a map that clearly delineates boundaries for districts where different land zoning standards will apply. Air, on the other hand, remains stable for only relatively short periods, and it is not possible to be similarly precise in delineating air zones. Also, since air moves in large masses which display similar characteristics or which cannot feasibly be divided, individual air zones have to be considerably larger in area than land zones, perhaps as large as several neighborhoods within a city, or even entire municipalities. Finally, because air pollution pays no heed to zone boundaries, large transition areas between zones of higher and lower air quality are an important part of air zoning.
Time. — In implementing air zoning, time is measured in a frame of reference wholly different from that of land zoning. It is considered in terms of hours instead of years. Changes in land use are much less variable over time than is the pollution-dispersal capacity of the atmosphere which can vary markedly within a few hours or even less, for example, because of changes in wind velocity. Because of these variations, there is a need to adjust source control regulations not only to the requirements of each zoning district but also over time in accordance with the quantity of air available to disperse pollutants.
Thus air zoning standards, as translated into source control or emission regulations, have a time dimension as well as a space dimension and must therefore incorporate a type of flexibility not necessary in land zoning. The long-term source control regulations which vary from district to district are based on desired standards in each zoning district, on the nature of the pollutant, and the relation of the emitter to other emitters and to receptors. Variations from hour to hour are also based upon these factors but with the addition of the short-term meteorological conditions. Together, they produce regulations that can be applied quickly to meet ever changing conditions. These regulations might include: (1) a fixed limitation on the amount and manner of pollution emitted under all conditions; (2) storage of pollutants during unfavorable dispersal conditions and emission during more favorable conditions; and (3) decreasing production, or complete prohibition under particularly severe conditions, e.g., when a temperature inversion causes pollution concentrations that endanger health. The degree of utilization of each of the alternatives would vary between the zones.
Air Resource Management
The traditional basis for the control of air pollution is the concept of "nuisance," that one man’s property ought to be free of deleterious effects produced by activity on another’s. This concept, in fact, has been the basis for most of the pollution control ordinances enacted until a few years ago. Nuisance control is almost impossible to apply when the pollutant is not directly traceable to its source or when the problem arises not from a single large emitter, but from thousands of small ones. As a result, few controls had been placed on the emitters of those gases that are odorless and invisible but which often cause considerable damage, nor had they been placed on the emitters of soot and smoke which individually had little effect on property but which contributed to the overcall community air pollution level.
To overcome this deficiency, the process known as the "air resource management study" has been developed and applied to an increasing number of communities throughout the country. The prime mover behind this approach has been the Division of Air Pollution of the U. S. Public Health Service which has made grants and technical assistance available for its utilization.
Air resource management begins with the recognition that modern man’s activities inevitably pollute the atmosphere. It recognizes, too, that the atmosphere has a role to play in the disposal of wastes, so long as wholly effective source controls are not economically feasible. Some pollution is therefore unavoidable under present economic and technological conditions. The objective at the present time is to keep the concentration of each pollutant below the dispersal capacity of the atmosphere and to reduce the harmful effects both to the immediate area and to the community as a whole.
The steps to be taken in developing an air resource management plan are described in Appendix A. They are listed in three phases: (A) Surveys, to assemble and acquire the necessary data on area conditions; (B) Analyses of present and future conditions and needs, as guides for considering practical alternatives for air quality control actions; (C) Decisions to determine the specific actions to be taken.4 Although the basic approach of this plan is applicable to virtually all communities, modifications of some of the steps may be necessary to suit particular situations.
This approach is closely related to and, in fact, should be used in conjunction with the comprehensive plan for the community. The steps to be taken are analogous to those of comprehensive planning and should take their proper role along with other planning considerations such as land use, demography, transportation, and waste disposal to which air quality is closely related.
Scale of the Study
An air resource management study should ideally be performed for an area covering an entire air basin. For the purposes of pollution analysis an air basin may be defined as the area encompassing the body of air in which the major pollutants originate and collect and in which the principal effects occur. (The term "airshed" as used in California is generally applied to an area clearly defined by topography.)
In many cases, this area would be more or less coterminous with a metropolitan area. When an air basin covers several communities, pollution problems cannot be solved by communities acting alone. An air pollution control agency at the regional level should be given power to perform the studies and establish the minimum standards for an entire air basin. As will be described, a number of conditions may produce significant variations in pollution levels within a relatively small area, but local conditions can only be considered within the regional context if the overall level of pollution is to be reduced.
Descriptive Mathematical Models
The analysis phase of the air resource management study includes the calculation of diffusion (or dispersal) equations which describe mathematically what happens to the pollutants after they are emitted into the atmosphere. For example, the analyses help answer the following questions for each area in the region: Do pollutants tend to concentrate in the immediate vicinity of the source? Do they tend to disperse over a large area? Or do they remain concentrated and reach the surface at some distance from the source?
Detailed knowledge of such characteristics as pollution sources, topography, meteorology and micrometeorology, and land use of each of the subareas of the community can be used to calculate the diffusion equations and to prepare mathematical models describing the relative contribution of the sources in each subarea to the pollution concentration of other areas and of the region. Mathematical models can also represent characteristics of the air mass both horizontally and vertically. (Vertical boundaries in many urban areas are usually defined by an inversion layer, the point at which warmer air overlies a body of cooler air, in reverse of the more common situation in which temperature decreases with height. Such a layer effectively seals off the upper atmosphere and increases the concentration of pollutants below it. The Los Angeles basin is one of the more extreme examples but many communities, even those located in relatively flat terrain, such as Chicago and St. Louis, are often subject to inversion.)
Considerable success has been achieved in several air resource management studies in producing mathematical models which accurately describe the pollution levels for each part of the area.5 As will be discussed, models are also useful in forecasting the effects of the introduction of a new emitter or emitters into the area and in describing the effects of the various controls.
Airflow is an important determinant of the level of air pollution. Airflow studies indicate how long a given body of air remains stagnant, how often it is replaced, and how many times the same body of air passes over the sources and receptors of pollutants. The flow of air, in turn, depends upon meteorological and topographical conditions, land use traffic patterns, natural landforms, and other factors. Air monitoring stations located throughout an urban area and analysis of the samples they yield can lead to the preparation of hourly airflow maps with a fairly high degree of accuracy. Such maps have achieved a degree of operational utility in Los Angeles.
When complaints are received by the air pollution control district, the complainants are located on a grid which is placed over one map indicating the airflow at that time and another showing known emitters of the pollutant. It may then be possible (admittedly with many limitations), to trace the pollutant to its source. The use of automatic data processing machines to isolate sources and plot trajectories, as well as to add such other data as wind turbulence, has simplified the process and increased its utility.6
Airflow maps are also of considerable value in determining the contribution of single (point) sources and area sources to the pollution level over the entire community and over each section of the community. Because the dispersal of pollutants depends to such a great extent on wind conditions, the preparation of airflow maps and diffusion equations is one of the key steps in the process of determining effective air quality standards for different parts of the community.
Air Quality Standards
Air zoning like other forms of sophisticated air pollution abatement rests on the establishment of air quality standards or objectives which define the acceptable concentration of each pollutant in the atmosphere. These standards in turn are used to determine emission controls. It must be reemphasized that the standards of air quality are not the end product; they are used in the subsequent calculation of allowable emission rates or other controls (e.g., location of emitters, combination of emitters, and possible limitation on the number of emitters) that will maintain the standard.
Left, a view southwest from the Chicago Loop during an extended temperature inversion period; right, approximately the same area on a clear day with the only visible smoke plume coming from the southwest sewage treatment plant. The tall building in both photographs is the administration building of the University of Illinois, Chicago Circle Campus.
While air quality standards contemplate some pollution in the atmosphere, they are not intended to define a precise line above which detrimental effects are likely to occur and below which they will not occur. The concentration indicated as a standard merely represents the approximate level at which detrimental effects may be expected to begin to occur or, conversely, the approximate level of concentration below which the effects defined will not ordinarily occur.
The concept of air quality standards can be simplified by reference to the following equation:
If: C = the concentration of contaminants in the atmosphere,
Q = the quantity of wastes, and
V = the volume of air into which the wastes are disposed,
Thus, if the concentration of a pollutant increases above a permitted level, i.e., the level of the adopted air quality standard, either the quantity of pollution must be decreased or the available air supply must be increased to disperse it. Obviously, then, if the volume of the air mass cannot be changed appreciably as desired, and under present technology it cannot, then pollution emissions must be reduced. The air quality standards can be used to define the amount by which the quantity of each pollutant must be reduced. In this approach of back-calculation from a desired objective of air quality, the impact of the controls is known beforehand; for regulations based simply on source controls, on the other hand, the end result is only an educated guess.
Although the major reason for controlling air pollution is to prevent its interference with physiological functions, any decrease in the normal functioning of the community as a result of air pollution is a cost to the community and is a basis for the determination of standards. Therefore, ambient air quality standards should be designed to minimize the cost of air pollution by a reduction in (1) the danger to human health and well-being, (2) damage and injury to vegetation, (3) damage and injury to domestic animals, (4) damage to materials and property, and (5) interference with visibility. The utilization of these concepts in the establishment of standards is discussed in the following sections.
Criteria for the Standards
It would, of course, be desirable to set air quality standards for all pollutants, but research into their effects has not progressed to the point where objective criteria can be determined for each pollutant. There are adequate criteria for some contaminants; for others, there are only partial criteria; for still others, no objective criteria have been formulated.
Biological experimentation has indicated that certain pollutants may be toxic to animals, for example, but little information is available as to the effects of small concentrations on humans. New York, among others, has established standards (called objectives) for some gaseous contaminants based on the considered judgment of experts on air pollution such as engineers, physicians, and meteorologists. It was felt that lack of complete information about the effects of some pollutants was not sufficient reason to assume that no detrimental effect exists. In addition, some communities and states have set standards for sulfur oxides, suspended particulates, dustfall, and some others for which the criteria have not as yet been spelled out. It is understood that these necessary but, to an extent, arbitrary controls may be changed when additional information becomes available.
The criteria are in turn based upon the lower of the long-term exposure concentration and the threshold concentration, i.e., the adverse effects produced by extended exposure to a pollutant and those produced by high concentration over a short period. In either case, where sufficient information is not available, it may be necessary to leave a margin of safety greater than might actually be necessary.
The Economic Bases for Standards
One of the key steps in any air resource management study is a comparison of the marginal costs of the various control methods and devices with the effects they have on reducing pollution levels. This means in effect that any control district wishing to institute an air pollution abatement program will need to decide the level of air quality it desires to attain and the costs it is willing to incur to reach this level. Because there are so many variables, the degrees of compromise that may be reached by different communities will undoubtedly vary considerably.
One of the key variables in the determination of air pollution control methods is cost. Cost can be classified under two major headings: (1) the costs to a community that are a direct result of the existence of the pollutant and (2) the costs which a community incurs to control the pollutant. The first can be broken down into (A) direct economic costs, i.e., those which can be evaluated relatively easily in terms of dollars (such as crop damage and corrosion of materials); (B) indirect economic costs, e.g., out-migration of citizens or losses due to poor visibility; (C) health hazards for which it becomes almost impossible to assign costs; (D) social costs as a result of increased movement of the citizens in an attempt to find relief from contaminated air, and (E) psychological costs produced as a result of the fear of pollution-induced illness.
The costs of control are categorized as (A) primary, those which prevent the production of pollutants; (B) secondary, those which permit production but which limit emission; (C) tertiary, those controls which permit emission but prevent the occurrence of harmful effects.
The determination of standards, i.e., the maximum concentration of each pollutant that a community is willing to accept, is based directly on the analysis of both the direct and indirect types of costs. However, because the costs due to the existence of a pollutant are distributed throughout the reception area and, therefore, are difficult to assess, while costs of control are usually out-of-pocket expenses and more readily determined, the latter have weighed more heavily in establishing air quality standards. Nevertheless, an air resource management study should try to determine all the costs in arriving at standards for each zone. The goal for each community should be to minimize the sum of the cost of the damage and the cost of control in each zone. But so long as the burden of the former is indirect and diffuse, and the burden of the latter is direct and more concentrated, coming close to the goal without actually attaining it may be all we can expect.
Variable Standards Within a Region
For the purpose of air zoning, one of the major tasks of an air resource management study is to determine whether variable standards are feasible and desirable within a given air basin. One community may be unwilling to accept a level of contamination that is acceptable to its neighbors. Or a city (or state) may be willing to accept a higher level of concentration in an industrial area than in a residential or recreational area. The responsible governing bodies could resort to air zoning to accomplish these objectives. But whether they have a realistic basis for doing so depends on the presence of those factors, discussed below, that produce local variations. There has been considerable discussion of this point among professionals in the field of air pollution control over the past few years, and the general consensus appears to be that in most regions there are significant local variations so that different standards can indeed be established.
Local meteorological conditions play an important role in determining the degree of contamination of the atmosphere and are the critical determinant of the feasibility of variable standards. Considerable research has led to the conclusion that there are significant areal differences within regions, even though local conditions can be analyzed only in the context of the entire region.
In determining zones as they apply to air pollution, the meteorological factors of most importance are: prevailing wind speed and direction, turbulence, the prevalence of temperature inversions, precipitation, and the periods of sunshine.
Where air monitoring stations have been maintained in an area over an extended period, it has been found that a variety of surface features might produce local meteorological differences which affect the dilution capacity of the atmosphere, i.e., the amount of pollution it can accept without producing harmful effects. These factors include physiographic features which hinder or facilitate air movements; location and form of green areas; type of land use; the density, orientation, site planning, and mass of buildings; and the location and density of traffic on major arteries. Air movement is caused by pressure changes produced to a large extent by the amount of heat generated or absorbed by the land. Thus such factors would produce considerable local variations in air flow. (The roughness of the surface, for example, would increase the turbulence of the air, thereby affecting the manner, location, and period of pollution dispersal.)
A general rule of thumb is that the concentration of pollutants from a single source varies inversely with the square of the distance from the source except under unusual conditions. Because concentrations fall off so rapidly, the major effects are generally felt relatively close to the source. (For industrial emitters with high stacks, however, there is usually considerable dispersal before the pollutants reach the ground.)
Since distance from the source plays such an important role even in a community located on a flat plain, it certainly appears feasible to establish variable standards for communities within a metropolitan area or even for individual neighborhoods if meteorological conditions permit.
Criteria for Variable Standards
Sensitivity of Receptors. — After the location of the emitters, the next most important criterion in determining varying air quality standards is the sensitivity of the various receptors to different pollutants. In any complex geographical area, the range of receptor sensitivity will be considerable. In a city, for example, some people will be much more susceptible than others to various contaminants; the same holds true for different kinds of vegetation in an agriculture area. Accordingly, as the pollutant concentration changes, different proportions of the total number of receptors experience ill effects.
But even more important, groups of receptors as a whole are affected differently by different pollutants. Some pollutants are more toxic to vegetation and to animals than to people, while some are not harmful to living things but may cause property damage. An agricultural area, for example, is more sensitive to sulfur dioxide and fluorides than is an urban area. On the other hand, hydrogen sulfide has little effect on vegetation but is malodorous and obnoxious to people and may even become poisonous in high concentrations.
Analyses of these types of data are directly related to the economic feasibility of emission controls. In the establishment of standards, a community must consider the cost of the available controls and the severity and seriousness of effects, which may provide a basis for determining the per cent of receptors which can be protected practicably.
The U.S. Public Health Service has taken the position that in terms of human health, standards should be based upon the most sensitive groups, e.g., the aged, the chronically ill, and the frail. P.H.S. is currently preparing guidelines using this criterion. It seems logical that a minimum standard relating to health for each pollutant should be established for an entire air basin. Individual communities might then adopt stricter standards to suit their own needs.
Over the last few years, there has been considerable discussion relating to the problem of a single versus a multiple standard for each contaminant. There is almost universal agreement that standards should be designed to maintain a level for each contaminant which would not impair the health or bodily functions of any individual, regardless of his sensitivity. It seems almost as likely, although there is little information to substantiate it, that the public will not accept standards permitting contamination levels which exceed the threshold for sensory irritation of taste or odor, or which would allow damage to livestock or agricultural crops. But there is little consensus in the areas of property damage and nuisance, i.e., soiling of fabrics, corrosion of building materials, and the reduction of visibility. Different receptors have different sensitivities to contaminants, and what the public is willing to accept may vary markedly from place to place.
Other Local Considerations. — If we assume that nonhealth-related standards can be established and enforced in relatively small areas, what factors should be considered in establishing the standards? These factors would all appear to boil down largely to a question of economics: the people of some communities are willing to spend more money to enforce higher standards than others. Using visible particulates as an example, the esthetic sensitivities of people in some areas may produce a desire to minimize the amount of dust and soot in the atmosphere. Or the people may wish to establish very strict limitations on certain gases which tend to deteriorate paint at a rapid rate.
It is reasonable to assume, therefore, that the wide range of goals exhibited by communities within any region would lead to a similarly wide range of air quality standards above the minimum health requirement. Until such time as controls based on a single high standard become economically feasible, variable standards are a satisfactory solution.
New York State's Ambient Air Quality Objectives
The most notable example of the application of different controls to zones within a large area is that under the jurisdiction of the New York State Air Pollution Control Board. After considerable study, including a continuing inventory of emission sources by small area throughout the state, the board has prepared a series of objectives for those substances which are known to be harmful as well as those which are likely to be harmful to people, livestock, vegetation, or property. These objectives have been broken down, using the criteria described in Appendix B, into four major and four minor categories. Each area of the state will eventually be assigned the objectives of the most applicable of the 16 possible categories.
The objectives were enacted by the legislature at the end of 1964, and thus far classifications for three counties, Chemung (Elmira), Erie (Buffalo), and Niagara (Niagara Falls) have been adopted and those for Westchester County are in the process of adoption. The map indicates the application of varying standards to an industrial region and its less-developed hinterland.
Area classification for air quality objectives, Erie County (Buffalo), New York. See Appendix B for description of objectives. (Map courtesy State of New York Air Pollution Control Board.)
Three of the four regional designations are indicated ("B," "C," "D,") with a number of subregional classifications under each. As indicated by the tables in Appendix B, the industrial city of Buffalo is permitted to maintain a higher concentration of the listed pollutants, while the standards permit decreasing concentrations with distance from the center. The smaller towns and villages are assigned standards slightly below those of their surrounding agricultural areas.
While this approach is certainly not ideal (partly because of its emphasis on political boundaries), it indicates one approach to the determination of air quality zones that might be applicable to areas in other states.
Updating the Standards
As has been emphasized throughout this report, air quality standards are adopted as the result of the study of sources, means of transfer, and the effects of pollutants. Not only do these conditions change but our ability to measure and to cope with them is improving rapidly. This combination would tend to render standards obsolete within a relatively short time; therefore, the information that forms the basis for standard-setting must be periodically updated, analyzed, and used for the revision of the standards.
An important part of the process of keeping the standards up to date is the maintenance of a continuous air monitoring program. The U.S. Public Health Service maintains a large number of air monitoring stations throughout the country. These may be supplemented by additional stations in various parts of a community. They serve an important function in providing information on the effectiveness of the controls and in determining the effects of the changing patterns of land and energy use on the air pollution level. These data would be fed back into the goal-setting and plan-formulation process with a revision of the controls, either up or down, as the result.
Pictured above are two examples of the more obvious types of pollution sources. On the left is a burning municipal dump in Joliet, Illinois, with a generating plant visible in the background. On the right is one of the most offensive sources, a chemical plant from which obnoxious odors are detectable at a considerable distance.
Applying Air Zoning Techniques
Operational Uses for Mathematical Models
In addition to their descriptive characteristics, mathematical models of the pollution characteristics of an urban area have considerable practical value. With the information that is available from the air monitoring program, they can be used to analyze air quality and determine when the maximum allowable concentration in each zone has been exceeded. They can assist in evaluating the desirability of various emergency measures, and they can help to evaluate the efficacy of various plans to reduce pollution levels. They also help to determine the effects of adding a large source of pollution or a number of sources to the existing total, to predict the pollution patterns likely to exist in the future as the urban area expands, and even to estimate the effects of various planning techniques on predicted pollution levels.7
Los Angeles again provides a good example of the sophisticated use of mathematical models for operational purposes. It has incorporated into its model a vast amount of data including a complete emission inventory. When, at any given time pollution levels reach progressively more severe concentrations, i.e., "adverse," "serious," or "emergency," progressively more drastic steps are taken to reduce emissions, such as stopping production at a selected group of plants. This application of graded air quality standards has proved its operational value.
Planners may also find mathematical models useful in testing various development alternatives to determine the level of air quality that would result. Air quality data, fed into the comprehensive planning process along with data on other predicted conditions, would become an additional criterion to be used in the selection of the best alternative. The pioneering work in this field is being done by the Northeastern Illinois Planning Commission and includes an air resources management study as an integral part of its comprehensive planning program.
Although an increasing number of communities are including performance standards for industrial zones in their zoning ordinances, the standards as they refer to emission rates have seldom been based on predetermined objectives of desirable air quality. The approach outlined in this report in one sense provides a rational basis for the use of performance standards.
It should be emphasized that so far as air zoning is concerned, there is no reason to exclude any industry from any part of an urban area. So long as limitations are placed on the amount of pollution which a source will be allowed to add both to the local level of pollution and to the over-all level, the industry will be free to choose its location and to select the most economical and convenient methods to control its emissions.
Utilization of air zoning also would indicate the need to apply performance standards not only to industries but to all types of uses including residential. The soot and dust that is the bane of the housewife is often not the product of a factory but the result of the incomplete combustion of a very low grade of coal (which also is a major source of sulfur dioxide in many urban areas) used in home heating. Across-the-board application of performance standards based on predetermined air quality standards would go a long way toward reducing both neighborhood and area-wide pollution.
The main purpose of this report has been to bring the problems of air pollution to the attention of planners and to outline one approach toward their alleviation. It is to be reemphasized that the utilization of the air zoning approach, or one similar to it, is a vital step in the maintenance of a healthful environment. Until such time as completely effective controls at the source become economically feasible, and that day is not in the foreseeable future, air quality standards must adjust to the needs and economic resources of individual communities.
An Air Resource Management Study: Methodology
Source: Vernon G. MacKenzie, Management of Our Air Resources. Paper presented at the Growth Conference on Air, Land, and Water Resources, University of California at Riverside, October 7, 1963.
1. Collect air quality data from previous studies and make such additional measurements as are necessary and practicable to define present air quality and serve as one basis for estimating future pollution levels.
2. Collect available meteorological data and make such further measurements as may be needed to calculate dispersion formulas. Items of principal interest here are: wind speed and direction; vertical temperature gradients; and frequency and duration of stagnation periods.
3. Collect information on local topographical features as they may affect pollutant dispersion and future land-use patterns.
4. Collect data on pollutant emissions. Possible sources include census data, Chamber of Commerce files, complaint files of public agencies, and traffic surveys. Questionnaires, field inspections, and some emission measurements may also be needed.
5. Review existing control programs and applicable laws, also related zoning, building, and nuisance control regulations.
6. Assemble information on anticipated developments, as to land-use patterns, population, and industrialization; and on technological changes which affect pollutant emission and control methods.
7. Collect available information, and possibly make new studies, on effects of pollutants on local health, vegetation, materials, visibility, and property values.
8. Study current plans for transportation, land use, and open spaces, to coordinate with them the air resource management plan. Keep other planners informed as the air plan develops.
1. Make projections of current and future pollutant emissions, considering changes in technology, population, industrialization, and transportation.
2. Develop mathematical models for estimating current and future air pollution levels, based on above emission projections and on meteorological data; and estimate levels which would result from several possible emission control programs and land-use patterns.
3. Indicate approximate cost of reaching each of those alternative levels; their possible impact on transportation and social patterns, need for industrial expansion, availability of fuels, and community aims; and their likely effects on health, materials, vegetation, visibility, etc.
4. Evaluate possible systems for collection, storage, and analysis of data needed, on a continuing basis, for the air resource management program.
5. Indicate various alternatives for implementing the program, as to jurisdictions to be served, legislation needed, appropriate control agencies, relationships with other jurisdictions, sources of funds, coordination with other local planning programs, and citizen participation.
C. Conclusions and Decisions
1. Select air quality standards — possibly with variations in various parts of the area.
2. Cooperate with other community planners in allocating land uses.
3. Design remedial measures calculated to bring about the air quality desired. Such measures might include several or all of the following: limitations on pollutant emissions; variable emission limits for certain weather conditions and predictions; special emission limits for certain areas; time schedules for commencing certain control actions; control of fuel composition; control of future sources by requiring plan approvals; prohibition of certain plan approvals; prohibition of certain activities or requirements for certain types of control equipment; and performance standards for new land uses.
4. Outline needs for future studies pertaining to air quality and pollutant emissions, and design systems for collection, storage, and retrieval of the resultant data.
5. Establish priorities among program elements and set dates for implementation.
6. Prepare specific recommendations as to administrative organization needed to implement the program; desirable legislative changes; relationships with other agencies and programs, in the area and adjoining areas and at higher governmental levels; and funds, facilities, and staff required.
State of New York Air Pollution Control Board
Ambient Air Quality Objectives
(Statutory authority: Public Health Law, §§ 1271, 1276)
500.2 Basis of ambient air quality objectives
500.3 Application of objectives
Section 500.1 Foreword. (a) Ambient air quality objectives describe a level of air quality designed to protect people from the adverse effects of air pollution; and they are intended further to promote maximum comfort, and enjoyment and use of property consistent with the economic and social well-being of the community.
(b) The basic use of our air resource is to sustain life. Our environment is an ocean of air, of which the average adult male must inhale approximately 400 cubic feet daily to obtain the necessary oxygen. Air entering the respiratory tract must not menace health. Therefore, all other uses must yield to the necessity of air which will not degrade, either acutely or chronically, the health and well-being of the populace.
(c) The only areas of compromise are the economic and the esthetic. In these areas the cost to society of providing a given level of air quality must be balanced against the benefits attained. As a consequence, in many communities, achievement of a desired air quality will be realized through a number of transition periods, during which improvements will be made as advancing technology reduces the cost of cleaner air.
(d) Ambient air quality objectives as used here are a tool in achieving cleaner air, not as a license to permit unnecessary degradation of air quality which would thwart attainment of the long-range goal to maintain a reasonable degree of air purity. They have been designed, and should serve, as a sound basis in the development of contaminant emission limitations, in the preparation of long- and short-range objectives for acceptable total contaminant limitations, and for the selection of air pollution control measures for planned and existing establishments which may create pollution.
(e) These objectives are not intended to represent the ultimate in air quality achievement. It is anticipated that research and development will gradually make possible cleaner air at lower cost.
(f) It has not been possible at this time to establish acceptable limits for many contaminants because of the dearth of information regarding the threshold values which might be harmful to the receptors. This is an area of research which will require additional attention by environmental health investigators. As evidence accumulates on the deleterious effect of a contaminant, present objectives will be revised or additional objectives established.
(g) The current ambient air quality objectives are tabulated in Tables I, II, III, IV, V, and VI (see Appendix 2) [pages 22–25]
(h) Analytical treatment of samples in determining contaminant concentrations is listed in Table VII (see Appendix 2). These laboratory procedures will be revised as improved methods are developed. In unusual instances, other sampling and analytical procedures that may be used to determine compliance with objectives shall be subject to board approval.
500.2 Basis of ambient air quality objectives. (a) The degree of air purity required may depend on the effect on any or all of the following receptors: man, livestock, vegetation, and property. This is especially so, for example, with some of the pollutants, such as fluorides, which not only damage vegetation, but also may build up concentrations in forage crops toxic to grazing ruminants. When protection of human health is of concern, the objectives must be set so as to assure no adverse effects. Otherwise, objectives in whole or part must be based on the potential effects on susceptible receptors and accepted or potential land uses.
(b) Air pollution potentials range from the almost pristine pure air such as is found in the Adirondack Mountains to the heavily contaminated air in the highly populous and industrialized areas such as the Niagara Frontier and Metropolitan New York. Within this range, the degree of social and economic development accounts for the kind and quality of contaminants emitted to the atmosphere and hence the potential effect on the receptors. These factors in combination with topographical and meteorological variations would tend either to accentuate or reduce the effect of emissions.
(c) Thus, it is illogical to attempt one overall set of quality objectives to apply to the entire State. It cannot be expected that the board can permit air in a clean area — for example, one used principally for high quality purposes such as recreation — to be degraded to a level that can reasonably be attainable in a highly populated and industrialized area. Nor would it be reasonable to expect a highly industrialized area to attain economically the level of air quality prevailing in the presently clean areas.
(d) The results of air sampling surveys for settleable and suspended particulates, conducted for the board by the Bureau of Air Pollution Control Services in the State Department of Health, show that four distinct general levels of air contamination exist in the State. These levels appear to be related generally to the macro-population density and related economic development. It therefore seems logical to establish four major regional classifications.
(e) Within any region, land use varies, but broadly falls into four types: industrial, commercial. residential, or rural. In essence, these land use types describe the activity that creates the varying degree of air contamination. The land uses can be defined as follows and describe the subregions into which each region is subdivided:
Subregion 1 — predominately used for timber and agricultural crops, farming, and recreation. Habitation and industry sparse.
Subregion 2 — single- and two-family residences, small farms, and limited commercial services and industrial development.
Subregion 3 — densely populated, primarily commercial, office buildings, department stores, and light industry such as electronics and instruments, apparel and finished products, printing and publishing, and food and kindred products.
Subregion 4 — primarily industrial, light and heavy industry such as chemical and allied products, primary ferrous and nonferrous metals, stone, clay, glass, petroleum, and coal.
(f) It is with these factors in mind that regional and land use air quality objectives have been established. This is in keeping with the Air Pollution Control Act, which charges the board with the responsibility of promulgating air quality objectives following surveys to determine levels of contamination, recognizing varying requirements for different areas of the State.
(g) Extreme toxicity to humans of some contaminants, such as beryllium compounds, requires the establishment of one maximum allowable concentration in all areas.
(h) Toxicity to animals of some contaminants, such as fluorides, requires the establishment of stringent maximum allowable concentrations where the effects are likely to interfere unreasonably with the economy of the area.
(i) The public welfare and the protection of physical property and other resources require the establishment — based on what can be reasonably achieved in keeping with the social and economic development of the area — of maximum allowable concentration for some other contaminants.
500.3 Application of objectives. (a) Definition of geographical boundaries of regions and subregions and their classification will logically follow the completion of comprehensive area surveys. Based on the findings and following public hearings, as required by law, the board will then establish the objectives applicable to the areas studied.
(b) It is the intent of the board to evaluate attainment of AAQ objectives on the basis of avoiding adverse effect on a receptor. It is therefore logical to establish attainment by employing any reasonable method or combination of methods such as area sampling, source sampling, emission evaluation, and assessment of source contribution and effect.
(c) It is the intent of the board to control emissions to the extent that emissions in one classified area will not contravene the objectives in another classified area.
New York State Air Pollution Control Board Ambient Air Quality Objectives
New York State Air Pollution Control Board Ambient Air Quality Objectives
(24 hr. averages, except as noted. to be less than given values)
|Sulfuric Acid Mist||0.10 mg/m3||all|
|Hydrogen Sulfide||0.10 ppm for 1 hr.||all|
|(To be less than given value 85% of the time on an annual basis)||15 ppm for 8 hrs.*|
|(To be less than given value 100% of the time)||30 ppm for 8 hrs.*|
|(To be less than given value 99% of the time on an annual basis)||60 ppm for 1 hr.*|
|Oxidants (Incl. ozone. photochemical aerosols, and other oxidant contaminants not listed separately)||0.05 ppm
0.15 ppm for 1 hr.
0.10 ppm for 4 hrs.
1 & 2
|Fluorides (as HF) in air||1 ppb
|Soluble Fluorides (as F) in forage for livestock consumption — dry weight basis||35 ppm**||1 and 2|
**Values above 35 ppm will be acceptable provided it can be shown that no adverse effects are created and provided it can be shown to the board's satisfaction that the average over four consecutive months does not exceed 35 ppm.
The ambient air shall not contain visible smoke from any fuel-burning equipment (including incinerators) which is inconsistent with the economic or social well-being of the community or which will prevent enjoyment and use of property. The foregoing also applies to open burning of refuse, where permitted.
Consistent with the economic and social well-being of the community, the ambient air shall not contain odorous substances in such concentrations or of such duration as will prevent enjoyment and use of property.
The ambient air shall not contain any radioactive substances in concentrations that are deleterious, either directly or indirectly, to human health, or which affect the economic or social well-being of the community.
Other Toxic or Deleterious Substances
The ambient air shall not contain toxic or deleterious substances, in addition to those specifically listed in these objectives, in concentrations that affect human health or well-being, or unreasonably interfere with the enjoyment of property, or unreasonably and adversely affect plant or animal life. Guides for specific substances will be considered on an individual basis by the board.
Glossary of Selected Technical Terms
Air Basin. — A term used by the U.S. Public Health Service to indicate the area in which the major pollutants originate and collect and in which the principal effects occur.
Air Conservation. — The opposite of air pollution. The maintenance of an air supply as free from contaminants as is possible.
Air Dilution Capacity. — The amount of pollution that a given body of air can absorb without increasing the concentration above maximum accepted levels. It is a function of such things as physical boundaries, speed and direction of airflow, temperature, and others.
Air Quality. — The amount of pollution contained in a given body of air.
Air Quality Standards and Objectives. — The concentration of each type of pollutant that is considered to be acceptable in any area. They are established subsequent to detailed studies of sources and effects of pollution among other things and are used to establish permitted emission rates. They are usually enacted into law.
Air Resource Management Study. — A process in which sources and effects of pollution are analyzed, objectives relating to desired levels of air quality are formulated, and emission controls are instituted. It accepts the premise that air pollution is an inevitable concomitant of modern life but that the air resource is in the public domain and must be maintained as pollution-free as is possible.
Air Shed. — A term that often is used synonymously with air basin but which has come to mean an area that is more clearly defined by topography.
Ambient Air. — The air supply moving past and enveloping a pollution source and that carries the pollutants away from the source.
Diffusion Model. — A mathematical representation, usually constructed with the aid of electronic computers, which describes emission sources and airflow characteristics of an air basin. It is used to determine the relationship between sources and receptors and to calculate the probable pollution patterns resulting from various development alternatives.
Long-Term Exposure Concentration. — The effects resulting from extended exposure to a pollutant.
Micrometeorology. — Usually defined as relatively small-scale, localized disturbances of the atmosphere such as land and sea breezes, the flow of air down a mountain, showers, thunderstorms. and so forth. Depending on the scale of analysis, however, the term might include such things as the high- and low-pressure systems shown on the weather maps or, at the other end of the scale, local weather variations produced by small topographic changes and human activities.
Temperature Inversion. — A meteorological phenomenon in which a warm layer of air overlays a cooler layer. This condition precludes the vertical flow of air and prevents pollutants from escaping into the upper atmosphere.
Threshold Concentration. — The effects resulting from short-term exposure to a high concentration of a pollutant.
Trajectory. — The curve which an object describes in passing through space. Trajectories of pollutants are used to trace the source from the point of contact using airflow maps.
Turbulence. — The "gustiness" of the wind. The process by which small masses of air vary from the mean direction and disperse the particles which they carry. May be produced by topographical variations as well as such things as buildings, industrial activity, and agriculture.
1. Evelyn, John. Fumifugium: or the Inconvenience of the Aer, and Smoke of London Dissipated. Oxford, 1661. 43 pp. Reprinted by the National Smoke Abatement Society, Manchester, 1933. Quoted in: Man’s Role in Changing the Face of the Earth. William L. Thomas, Jr., Ed. Chicago: The University of Chicago Press, 1956. p. 586.
2. Frenkiel, Francois N. Atmospheric Pollution and Zoning in an Urban Area. Air Pollution Control Association Annual Meeting Paper No. 55-4, Detroit, Michigan, May 1955. Reissued with some revisions as "Atmospheric Pollution in Growing Communities," The Smithsonian Report. Washington, D.C.: Smithsonian Institution, 1956. pp. 269–299.
3. Stern, Arthur C. "Summary of Existing Air Pollution Standards," Journal of the Air Pollution Control Association, Vol. 14. No.1, January 1964, pp. 5-14; and in a letter to the author from Alexander Rihm, Jr., Executive Secretary, State of New York, Air Pollution Control Board, March 28, 1966.
4. MacKenzie, Vernon G. Management of Our Air Resources. Paper presented at the Growth Conference on Air, Land and Water Resources, University of California at Riverside, October 7, 1963.
5. Williams, James D., and Edmisten, Norman G. Air Resource Management Plan for the Nashville Metropolitan Area. Cincinnati: U.S. Department of Health, Education, and Welfare, Public Health Service, Division of Air Pollution, September, 1965; Venezia, R.A. Air Pollution Emission Inventory St. Louis - East St. Louis Metropolitan Area. Air Pollution Control Association Annual Meeting Paper No. 65-73, Toronto, Ontario, Canada, June 1965; and Dickinson, J.E. Air Quality of Los Angeles County. Air Pollution Control District, County of Los Angeles, 1961.
6. Herring. Frances. "Effects of Air Pollution on Urban Planning and Development," Proceedings, National Conference on Air Pollution. Washington, D.C., December 10–12, 1962, pp. 190–200.
7. American Association for the Advancement of Science. Air Conservation. The Report of the Air Conservation Commission of the AAAS. Washington, D.C., 1965, p. 55.
The following list represents the more notable of the works reviewed for the preparation of this report. Those of particular value to the reader are indicated by an asterisk.(*)
Air Pollution Control Programs Under the Clean Air Act. Washington. D.C.: U.S. Department of Health, Education, and Welfare, Public Health Service, Division of Air Pollution, 1965.
Air Pollution in Greater Elmira, (Area Survey No.1), and Air Pollution in Westchester, (Area Survey No.5). Albany: State of New York, Air Pollution Control Board, 1965.
*American Society of Planning Officials. Air Pollution: A Growing Urban Problem. ASPO Planning Advisory Service Information Report No. 79. Chicago: ASPO, October, 1955.
*American Society of Planning Officials, Air Pollution Control. ASPO Planning Advisory Service Information Report No. 20. Chicago: ASPO, November, 1950.
Atkisson, Arthur A. Air Contaminants as Factors in Industrial Land Use Planning and Zoning. Speech before the Northern California Section, AIP, San Jose, California, July 25, 1956.
*Dunsmore, Herbert J. "The Use of Air Quality Standards in Local or Area Control Programs," Journal of the Air Pollution Control Association, Vol. 14, No.8, August, 1964, pp. 320-321.
Frenkiel, F.N. The Physical Scientist's View of Air Conservation. Paper presented at the Annual Meeting of the American Association for the Advancement of Science, Cleveland, December, 1963.
Gabell, Katherine N. Clearing the Air: A Regional Challenge. Penjerdel (Pennsylvania-New Jersey-Delaware Metropolitan Project, Inc.), Philadelphia, 1963.
Goldner, Lester. "Air Pollution Control Should Be A Built-In Element of Community Development," Journal of Housing, Vol. 21, No.8, September, 1964.
*Herring, Frances W. "Basis for Urban Development: Air," Planning 1963 Proceedings of the American Society of Planning Officials National Conference. Chicago: ASPO, 1963, pp. 32–39.
Holland, W.D., Hasegawa, A., Taylor, J.R., Kauper, E.K. Industrial Zoning As A Means of Controlling Area Source Air Pollution. Air Pollution Control Association Annual Meeting Paper No. 59-64, Los Angeles, June, 1959.
"The Industrial Control Story," Report. County of Los Angeles, Air Pollution Control District, Los Angeles, April–June, 1958.
Katz, Morris. "Air Pollution and Community Planning," Canada's Health and Welfare, March, 1962.
MacKenzie, V.G. "Future Outlook for the Development and Application of Air Quality Standards," Journal of the Air Pollution Control Association, Vol. 14, No.1, January, 1964, pp. 19–21.
Maga, John A. Air Resource Management in the San Francisco Bay Area. Berkeley: Institute of Governmental Studies, University of California. 1965.
Pack, Donald H. "Meteorological Tools in Evaluating and Reducing Effects of Air Pollution," Journal of the Air Pollution Control Association, Vol. 14, No.3, March, 1964.
Pelle, William J., Jr. Bibliography on the Planning Aspects of Air Pollution Control: Summary and Evaluation. The Northeastern Illinois Planning Commission, Air Resources Management Study, December, 1964. (Unpublished)
Perkins, W.A. "Some Effects of City Structure on the Transport of Airborne Material In Urban Areas," Air Over Cities. Symposium sponsored by the U.S. Public Health Service, Cincinnati, November, 1961, pp. 197–206.
Staff of the Committee on Public Works, U.S. Senate. A Study of Pollution — Air. Washington, D.C.: U.S. Government Printing Office, 1963.
Rihm, Alexander, Jr. "New York State’s Classifications—Ambient Air Quality Objectives System," Journal of the Air Pollution Control Association, Vol. 15, No. 11, November, 1965, pp. 519–522.
Salzenstein, Marvin A. Industrial Performance Standards for Zoning: A Current Review. Air Pollution Control Association Annual Meeting Paper No. 65–12, Toronto, Ontario, Canada, June, 1965.
Singer, I.A. An Objective Method for Site Evaluation. Air Pollution Control Association Annual Meeting Paper, June, 1959, 13 pp.
Stern, Arthur C., ed. Air Pollution. New York and London: Academic Press. 1962, 2 volumes about 1200 pp.
*Sutermeister, Oscar. Influence of Town and Country Planning on Air Pollution in the U.S.A. Paper presented at the European Conference on Air Pollution, Strasbourg, France, 24 June–1 July, 1964.
*Taylor. J.R., Hasegawa, A., and Chambers, L.A. "Control of Air Pollution Through Site Selection and Zoning," Air Pollution. Geneva: World Health Organization, 1961, pp. 293–306.
A Compilation of Ambient Air Quality Standards and Objectives. Cincinnati: Technical Assistance Branch, Division of Air Pollution, Public Health Service, U.S. Department of Health, Education, and Welfare, R.A. Taft, Sanitary Engineering Center, May 11, 1965.
Tilson, Seymour. "Air Pollution," International Science and Technology, June, 1965, 11 pp.
Wexler, Harry. "The Role of Meteorology in Air Pollution," Air Pollution. Geneva: World Health Organization, 1961, pp. 49–62.
Wronski, W., and others. Air Pollution Considerations in Planning and Zoning of a Large Rapidly Growing Municipality. Air Pollution Control Association Annual Meeting Paper No. 65-10. Toronto, Ontario, Canada, June 1965.
ASPO acknowledges the contributions of the following people toward the preparation of this report:
William Pelle and Kenneth Johnson, Air Resources Management Study, Northeastern Illinois Planning Commission; S. Smith Griswold and William Skwersky, Division of Air Pollution. U.S. Public Health Service, Washington, D.C.; Alexander Rihm, Jr., New York State Air Pollution Control Board; C.E. Moore, Loyola University; James D. Williams, Robert A. Taft Sanitary Engineering Center, P.H.S., Cincinnati, Ohio; and F.N. Frenkiel, Editor, The Physics of Fluids, Washington. D.C., whose writings provide much of the background for this report and who kindly consented to review an early draft.
Photographs in this report courtesy of Northeastern Illinois Planning Commission.