Criteria of setting ambient air
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This document discusses criteria for setting ambient air quality standards. It outlines several factors that influence decision making for standards, including acceptable health risks, control costs, and scientific judgment. Standards are designed to protect public health from air pollution effects and may establish maximum concentrations. Primary standards protect health, while secondary standards protect welfare. Factors like meteorology, geography, exposure levels, health risks, economics and policies must be considered when setting standards.
Criteria of setting ambient air
- 1. Criteria of Setting Ambient Air Quality Standards: An Overview Dr. Animesh Kumar Scientist Air Pollution Control Division, NEERI, Nagpur - 440020 Preamble Air Quality Standard (AQS) values represent concentration of air pollutants in air that would not pose any hazard to human population. However, the realistic assessment of human health hazard necessitates a distinction between absolute safety and acceptable risk. Due to lack of comprehensive and conclusive data on environmental contaminants, scientific judgment and consensus play an important role in establishing acceptable levels of population exposure. Several factors influence the decision-making process concerning air pollution standard setting. For example, infinite health protection is unattainable; therefore, either society must decide what level of health risk is acceptable, a decision that will be made indirectly, since the societal investment in environmental pollution control will dictate the level of health protection to be achieved. Ambient Air Quality Standards (AAQS) are setup for protecting public health from adverse effects of air pollution and eliminating or reducing to a minimum, those contaminants that are known to be or likely to be hazardous to human health. Several approaches have been considered for setting air quality standards. Some of these are: i) using another community's air as the standard, ii) using as standard the quality of air that existed at an earlier time for which it was believed that adverse effects were either nonexistent or tolerable by the community, iii) using as standard the quality of air that exists in the community on certain days of good ventilation and iv) considering health protection - control cost relationship. (xxxvi)
- 2. Types of Air Quality Standards An "Air Quality Standard" is a description of a level of air quality, adopted by a regulatory authority as enforceable. Enforcement of AQS aims at evaluating the need for control action on emission sources for attaining compliance with the standards. AQS are of three types and these are: (i) ambient air quality standards, (ii) indoor air quality standards, and (iii) emission standards. National Ambient Air Quality Standards A National Ambient Air Quality Standard (NAAQS) is a uniform, national standard establishing the maximum permissible concentration of an air pollutant in the ambient air - the "portion of the atmosphere, external to buildings, to which the general public has access." The USEPA has setup two types of standards, viz. "Primary Standards" to protect health with a margin of safety and for "Secondary Standards" to protect welfare. Primary Standards Primary NAAQS define the acceptable concentration of an air pollutant in the ambient air - necessarily to protect health with adequate margin of safety. The Primary NAAQS are used to identify the following areas: • Air quality control regions • Attainment areas (those complying with the standard) and • Non-attainment areas (those in which the pollutant exceeds the standard) Secondary Standards Secondary NAAQS define the concentration of an air pollutant in the ambient air necessary to protect the "public welfare." Effects on welfare includes, but is not limited to, effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-
- 3. being, whether caused by transformation, conversion, or combination with other air pollutants. Contents of an Air Quality Standard Typically an Air Quality Standard (AQS) contains the information on type, of pollutants, of their concentration and averaging time, of exposure (e.g. Outdoor etc), of compliance monitoring, of methods of data analysis, of QA / QC requirements, of nature of pollution effects, of likely adverse health effects, of special population (plant or material) at risk and of applicability (National, local, regional etc.) An AQS should also detail out; (i) supporting emissions standards for enforcing abatement measures in case AQS is exceeded, (ii) legislation, authorities responsible for public information, enforcement and penalties for exceeding standards, and (iii) provisions for informing the public about air quality. Setting of AAQS Ambient air quality standards are setup in such a way so that these can take care of all odds. Following factors should therefore be taken into account while setting AAQS: • Prevailing environmental conditions: This comprises; (i) meteorology (temperature, humidity, wind, turbulence) and (ii) geography (altitudes, natural sources of pollution, terrain) • Prevailing exposure levels of pollutants (including trends) • Prevailing social conditions • Prevailing economic conditions • Prevailing cultural conditions • Prevailing nutritional status • Prevailing policies (fuel policy, industrial policy etc.) concerning release of pollutants concentrations above or below guideline / standard values • Health risk of Chemical compound / pollutant and mixtures: epidemiology and toxicology (xxxviii)
- 4. • Any special populations (plant or material etc.) at risk and necessitating special attention Reasons for considering these aspects are summarized below: • At increased altitudes the partial pressure of oxygen falls and inhalation increases leading to increased intake of air borne particles. However, no increase in effects of gaseous pollutants would be expected. • Temperatures have significant effect on human health whereas humidity is unlikely to have significant effect on the toxicity of gaseous pollutants. • A total daily exposure of an individual to air pollution is the sum of the separate exposures to air pollution of that individual as he / she passes through a series of microenvironments during the course of the day (e.g. at home, while commuting, at works, etc.). Therefore Exposure in micro-environment = pollutants concentration x exposure time • Day to day variation in concentration of pollutants are affected by meteorological conditions responsible for dispersion • Database of time series epidemiological studies relates the daily occurrence of events such as deaths or admission to hospital to daily average concentrations of pollutants taking into account the confounding factors such as seasons, temperature and day of the week • People with poor standard of living suffer from nutritional deficiencies, infections disease due to poor sanitation and over crowding and tend to be provided with a poor standard of medical care. Each of these factors may render individuals more susceptible to the effects of air pollution • Exposure-response relationship of a pollutant may not be linear over the entire range of concentration of other pollutant: extrapolation beyond the available data may be dangerous. • Chemical composition of particulate matter may vary from place to place. (xxxix)
- 5. Priority Setting During setting of AQS, priority is given to several considerations which comprise; (i) avoiding the health risk, (ii) including air pollution compounds depending on toxicity exposure, (iii) emissions from most important sources of pollutants and (iv) most appropriate framework for a political, regulatory and administrative approach. Taking into the account all theses aspects guarantees consistent and transparent derivation of air quality standards and to ensure a basis for making decision on risk reducing measures and abatement strategies. The cost benefit analysis is also done so that the AQS is achievable. Enforcement of air quality standards Enforcement of an AQS should aim at evaluating the need for control action on emission sources to attain compliance with the standards. A typical enforcement plan should include; (i) a description of the area, (ii) an emission inventory and (iii) an air pollutant concentration inventory monitored and simulated. Though no monitoring programme, however, well funded and designed, can hope to comprehensively quantify patterns of air pollution in both space and time. Reliance on modeling alone is not sufficient. Although modeling can provide powerful tool for interpolation, prediction and optimization of control strategies, they are effectively useless unless properly validated by real-world monitoring data. Monitoring, modeling and emission assessments should be regarded as complementary components for estimating exposure or determining compliance. Some considerations to be done before enforcement are: • A comparison of emissions with air quality standards or guidelines • An inventory of effects on public health and the environment (xl)
- 6. • A causal analysis of the effects and their attribution to individual sources • Control measures their costs • Transportation and landuse planning • Enforcement procedures • Resource commitment • Projection for future Exposure to air Pollutants: Some Considerations Ideally human exposure study would be based on direct measurements of each pollutant concentration in the breathing zone of each member of a representative cross section of population of interest. However, such a programme is technically impossible and impractical as well. Personnel monitors may be helpful but they can be applied in a small sample of the population. Therefore, ambient air quality measurements at fixed sites are widely used as surrogate for population exposure. But the concentration may differ from those in breathing zone of residents of the community. Indoor air pollution: In ventilated buildings with open windows and no source of indoor pollution, outdoor concentration of pollutants almost equal indoor concentrations. However, in air conditioned (hot or cold) buildings the out door concentration gets largely attenuated during infiltration into indoor air, with indoor sources of pollution however, chemically reactive gases, such as 03 and S02 rapidly diffuse and react with interior surfaces. For non-reactive gases such as CO the indoor- outdoor concentration ratio is usually near unity. Fine particles' components such as Sulphate ion, the ratio of indoor outdoor concentration may be unity whereas coarse particle concentration indoor would be low due to deposition by sedimentation in relatively still air. (xli)
- 7. A complete knowledge of the concentration of all relevant pollutants in each microenvironment alone would not provide adequate basis for predicting physiological and pathological responses to human exposure as pollutant uptake could also be greatly affected by ventilation rate and pattern, entry of air via the nose or mouth, airway sizes, past and current history of another toxicants (such as cigarette smoke), and prior disease history and genetic dispositions. Help of models is, therefore, taken to estimate dose distributions associated with ambient air concentrations. A two-way approach is, therefore, generally used. This approach comprises; calculation of total tolerable intake for multimedia pollutants and subsequently, adequately partitioning the total tolerable intake among the different exposure routes taking into account the comparative importance of different routes of exposure for different pollutants An overview of the USEPA guidelines is discussed in the following text. United States Environment Protection Agency (USEPA) Criteria and the Process for Setting National Ambient Air Quality Standards (NAAQS): The EPA follows a multistage process for setting a NAAQS. The NAAQS is reviewed every 5 years using the same process, to ensure that the standard is based on the most recent scientific information. The basic steps of the process are as follows: > The listing by EPA of a pollutant that is emitted from numerous or diverse mobile or stationary sources and that endangers public health. > The preparation of a "criteria document" that summarizes the scientific information relevant to the pollutant; this document is formally reviewed by a Clean Air Scientific Advisory Committee (CASAC). (xlii)
- 8. > The preparation of a "staff paper" that summarizes the criteria document and lays out policy options for the Administrator; it is also reviewed by CASAC. > Based on the criteria document, the staff paper, and CASAC's "closure letters," the Administrator proposes a NAAQS; this proposal is published in the Federal Register, a "docket" created, and an opportunity for public review and comment provided and, > The Administrator's final decision, "which, in the judgment of the Administrator, is requisite to protect the public health" Several aspects in the NAAQS-setting process might be revisited: these include the Act's requirement that NAAQS be set to protect health with an adequate margin of safety, without consideration of costs; the process for verifying the scientific underpinnings of a proposed standard; the boundaries on the Administrator's judgment in accounting for risk and uncertainty in setting NAAQS; EPA's responsiveness to public comments; and the extent to which EPA must respond to requirements exogenous to the CAA that direct EPA to consider costs or other impacts of its regulations. Preparation of a Criteria Document Reviewing the scientific literature for all studies relevant to the air pollutant, the preparers consolidate information pertinent to: • The kinds and magnitudes of effects resulting from the pollutant's presence in ambient air • Assess the robustness of the studies • Endeavor to resolve inconsistencies • Evaluate findings Key components of the scientific evidence include: • Epidemiological studies that examine the relationships between ambient pollutant levels and public health and welfare (xliii)
- 9. • Clinical studies that examine human responses to controlled levels of pollutants, for example in air chambers • Animal studies Preparation of a Staff Paper Based on the criteria document, EPA scientists and policy experts prepare a staff paper. It is an administrative step designed to facilitate the EPA Administrator's decision. It lays out options for a, NAAQS standard e.g., whether to set a standard, at what level(s) it might be set, and methods for measuring compliance - along with justifications from the criteria document. Criteria Air Pollutants The pollutants for which NAAQS are set are often called "criteria pollutants." With the Clean Air Act Amendments of 1970, the EPA became responsible for determining national ambient air quality standards for the "criteria pollutants". Also, EPA was to assist states in attaining these standards through grants and technical assistance, and could impose sanctions on states for failures to fulfill their obligations. At present, six pollutants are designated "criteria pollutants" for which NAAQS have been set: particulate matter (PM), ozone (03, a key measure of smog), nitrogen dioxide (N02 or, inclusively, nitrogen oxides, NOx), sulfur oxides (SOx, or, specifically, S02), carbon monoxide (CO), and lead (Pb). National Ambient Air Quality Standards The CAA directs the Administrator to set a NAAQS at a level that provides protection from adverse effects on the public health and welfare. The Act provides for "Primary Standards" to protect health with a margin of safety and for "Secondary Standards" to protect welfare as discussed earlier. • The primary NAAQS does not itself establish what to do when concentrations exceed the standard (nor how to protect clean air in attainment areas). (xliv)
- 10. • For non-attainment areas, the States are required to prepare and implement state implementation plans (SIPs) to bring those areas into compliance. • Also, the federal government continues to prepare "guidance documents" spelling out available control measures for the NAAQS pollutants. • Finally, in attainment areas where the air is cleaner than NAAQS, the CAA establishes a program for new source permitting to "maintain" that clean air quality. Clean Air Scientific Advisory Committee (CASAC) The CASAC is composed of seven members including at least one member of the National Academy of Sciences, one physician, and one person representing State air pollution control agencies. It reviews the criteria and the NAAQS and recommends to the Administrator any new national ambient air quality standards and revisions of existing criteria and standards as may be appropriate. The committee also (i) advise the Administrator of areas in which additional knowledge is required to appraise the adequacy and basis of existing, new, or revised national ambient air quality standards, (ii) describe the research efforts necessary to provide the required information, (iii) advise the Administrator on the relative contribution to air pollution concentrations of natural as well as anthropogenic activity, and (iv) advise the Administrator of any adverse public health, welfare, social, economic, or energy effects which may result from various strategies for attainment and maintenance of such national ambient air quality standards. Public Comment / Public hearing For a reasonable period of time, the Administrator allows any person to submit written comments, data, or documentary (xlv)
- 11. information and gives interested persons an opportunity for the oral presentation of data, views, or arguments on the proposed NAAQS. Regulatory Impact Assessment (RIA) A regulatory impact assessment of the proposed NAAQS is carried out for potential economic impact on small entities, viz. industries, minorities and low-income populations. Cost-Benefits Analysis For proposed NAAQS, an analysis is carried out of, but not limited to, the following benefits: > The promotion of the efficient functioning of the economy and private markets > The enhancement of health and safety > The protection of the natural environment > The elimination or reduction of discrimination or bias and the following costs: > The direct cost both to the government in administering the regulation and to businesses and others in complying with the regulation > Any adverse effects on the efficient functioning of the economy, private markets (including productivity, employment, and competitiveness), health, safety, and the natural environment, Cost-benefit analysis is also carried out of potentially effective and reasonably feasible alternatives to the proposed NAAQS. (xlvi)
- 12. Following Table gives an idea of time taken by USEPA for Setting NAAQS for Ozone: August 1992 Ozone NAAQS review initiated Summer/Fall 1993 Workshops I Draft Criteria Document available to public and CASAC I994 CASAC meetings to review draft Criteria Document uj 'mm Spring 19S ipfs is|KI July 20 anc L . CASAC meetings to review revised draft of Criteria Marsh 20 and 21, ^ . 3 . . .. .. r „ 1995 < <•<• 4 'Document; also to review draft sections of Staff Paper September 19 andCASAC closure on Criteria Document; also closure on primary standard section of Staff Paper CASAC closure letter on Criteria Document sent to Administrator CASAC closure letter on primary standard section of Staff Paper sent to Administrator CASAC subpanel meeting on secondary standard section of Staff Paper CASAC closure letter on secondary standard section of Staff Paper sent to Administrator EPA publishes Advance Notice of Proposed Rulemaking (ANPR) for Ozone & PM NAAQS M 9 9 6 5 3 n d A U 9 U S t P " b l i c Meeting on ANPR 27 ^Proposed Decision announced/published in Federal Register, public comment period begins 20,1995 November 28,1995 November 30,1995 March 21,1996 April 4,1996 June 12,1996 November 1996/December 1996 January 14 and 1997 15, March 12,191. Winter/Spring 1997 June 25,1997 Late June 1997 July 16,1997 July 18,1997 July 18,1997 'MZMKmmmi Public Meetings in four cities on proposal End of public comment period on proposal Congressional hearings on the proposed NAAQS President Clinton endorses the proposed ozone & PM NAAQS, with some modifications EPA submits proposed final standards to OMB Administrator signs off on final Ozone & PM NAAQS Final NAAQS published in Federal Register First suit challenging the final standards filed in the U.S. Court of Appeals for the D.C. District Ozone & PM rules become effective (xlvii)