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Criteria Pollutants
EPA uses six "criteria pollutants" as indicators of air quality, and has established for each of them a maximum concentration above which adverse effects on human health may occur. These threshold concentrations are called National Ambient Air Quality Standards (NAAQS).
When an area does not meet the air quality standard for one of the criteria pollutants, it may be subject to the formal rule-making process which designates it as nonattainment. The Clean Air Act further classify ozone, carbon monoxide, and some particulate matter nonattainment areas based on the magnitude of an area's problem. Nonattainment classifications may be used to specify what air pollution reduction measures an area must adopt, and when the area must reach attainment. The technical details underlying these classifications are discussed in the Code of Federal Regulations, Part 81 (40 CFR 81).
The following is a discussion of the standards, designations and classifications of these areas.
OZONE
Ozone (O3) is a photochemical oxidant and the major component of smog. While O3 in the upper atmosphere is beneficial to life by shielding the earth from harmful ultraviolet radiation from the sun, high concentrations of O3 at ground level are a major health and environmental concern. O3 is not emitted directly into the air but is formed through complex chemical reactions between precursor emissions of volatile organic compounds (VOC) and oxides of nitrogen (NOx) in the presence of sunlight. These reactions are stimulated by sunlight and temperature so that peak O3 levels occur typically during the warmer times of the year. Both VOCs and NOx are emitted by transportation and industrial sources. VOCs are emitted from sources as diverse as autos, chemical manufacturing, dry cleaners, paint shops and other sources using solvents.
The reactivity of O3 causes health problems because it damages lung tissue, reduces lung function and sensitizes the lungs to other irritants. Scientific evidence indicates that ambient levels of O3 not only affect people with impaired respiratory systems, such as asthmatics, but healthy adults and children as well. Exposure to O3 for several hours at relatively low concentrations has been found to significantly reduce lung function and induce respiratory inflammation in normal, healthy people during exercise. This decrease in lung function generally is accompanied by symptoms including chest pain, coughing, sneezing and pulmonary congestion.
The 1-hour ozone standard, as well as designations and classifications for all 1-hour ozone nonattainment and maintenance areas, have been revoked except for the Greensboro, NC, Nashville, TN, and Denver, CO maintenance areas. See details here.
The following is provided for historical purposes:
The ozone threshold value is 0.12 parts per million (ppm), measured as 1-hour average concentration. An area meets the ozone NAAQS if there is no more than one day per year when the highest hourly value exceeds the threshold. (If monitoring did not take place every day because of equipment malfunction or other operational problems, actual measurements are prorated for the missing days. The estimated total number of above-threshold days must be 1.0 or less.) To be in attainment, an area must meet the ozone NAAQS for three consecutive years.
Air quality ozone value is estimated using EPA guidance for calculating design values (Laxton Memorandum, June 18, 1990). Generally, the fourth highest monitored value with 3 complete years of data is selected as the updated air quality value because the standard allows one exceedance for each year. It is important to note that the 1990 Clean Air Act Amendments required that ozone nonattainment areas be classified on the basis of the design value at the time the Amendments were passed, generally the 1987-89 period was used.
The strong seasonality of O3 levels makes it possible for areas to limit their O3 monitoring to a certain portion of the year, termed the O3 season. Peak O3 concentrations typically occur during hot, dry, stagnant summertime conditions, i.e., high temperature and strong solar insolation. The length of the O3 season varies from one area of the country to another. May through October is typical, but states in the south and southwest may monitor the entire year. Northern states have shorter O3 seasons, e.g., May through September for North Dakota. This analysis uses these O3 seasons to ensure that the data completeness requirements apply to the relevant portions of the year.
On November 6, 1991, most areas of the country were designated nonattainment or unclassifiable/attainment. These terms are defined as follows:
Nonattainment
any area that does not meet (or that contributes to ambient air quality
in a nearby area that does not meet) the national primary or secondary
ambient air quality standard for the pollutant.
Attainment
any area that meets the national primary or secondary ambient air
quality standard for the pollutant.
Unclassifiable
any area that cannot be classified on the basis of available information
as meeting or not meeting the national primary or secondary ambient air
quality standard for the pollutant.
Those areas designated nonattainment were also classified as follows:
Extreme
Area has a design value of 0.280 ppm and above.
Severe 17
Area has a design value of 0.190 up to 0.280 ppm and
has 17 years to attain.
Severe 15
Area has a design value of 0.180 up to 0.190 ppm and
has 15 years to attain.
Serious
Area has a design value of 0.160 up to 0.180 ppm.
Moderate
Area has a design value of 0.138 up to 0.160 ppm.
Marginal
Area has a design value of 0.121 up to 0.138 ppm.
Submarginal
Kansas City was the only area classified submarginal, but it has been
redesignated attainment. This category includes areas that violate the
ozone standard and have a design value of less than 0.121 parts per
million. This occurs when there is not a complete set of data so that
the estimated design value is higher than the ozone standard exceedance
rate of 1.0 per year even though the estimated design value is less than
the level of the standard.
Sec. 185A (Previously called Transitional) an area designated as an ozone nonattainment area as of the date of enactment of the Clean Air Act Amendments of 1990 and has not violated the national primary ambient air quality standard for ozone for the 36-month period commencing on January 1, 1987 and ending on December 31, 1989. Twelve areas were classified transitional in 1991. Section 185A. "Transitional Areas" lists the requirements for these areas.
Incomplete (or No) Data
an area designated as an ozone nonattainment area as of the date of
enactment of the Clean Air Act Amendments of 1990 and did not have
sufficient data to determine if it is or is not meeting the ozone
standard.
Sections 107(d)(4)(A) and 181 of the Clean Air Act lists the requirements for designations and classifications of ozone areas.
Ozone is the prime ingredient of smog in our cities and other areas of the country. Though it occurs naturally in the stratosphere to provide a protective layer high above the earth, at ground-level it is the prime ingredient of smog.
When inhaled, even at very low levels, ozone can: cause acute respiratory problems; aggravate asthma; cause significant temporary decreases in lung capacity of 15 to over 20 percent in some healthy adults; cause inflammation of lung tissue; lead to hospital admissions and emergency room visits [10 to 20 percent of all summertime respiratory-related hospital visits in the northeastern U.S. are associated with ozone pollution]; and impair the body's immune system defenses, making people more susceptible to respiratory illnesses, including bronchitis and pneumonia.
Children are most at risk from exposure to ozone. The average adult breathes 13,000 liters of air per day. Children breathe even more air per pound of body weight than adults. Because children's respiratory systems are still developing, they are more susceptible than adults to environmental threats. Ground-level ozone is a summertime problem. Children are outside playing and exercising during the summer months at summer camps, playgrounds, neighborhood parks and in backyards.
Asthma is a growing threat to children and adults. Children make up 25 percent of the population and comprise 40 percent of the asthma cases. Fourteen Americans die every day from asthma, a rate three times greater than just 20 years ago. African-Americans die at a rate six times that of Caucasians. For asthmatics having an attack, the pathways of the lungs become so narrow that breathing becomes akin to sucking a thick milk shake through a straw. Ozone can aggravate asthma, causing more asthma attacks, increased use of medication, more medical treatment and more visits to hospital emergency clinics.
Even moderately exercising healthy adults can experience 15 to over 20 percent reductions in lung function from exposure to low levels of ozone over several hours. Damage to lung tissue may be caused by repeated exposures to ozone -- something like repeated sunburns of the lungs -- and this could result in a reduced quality of life as people age. Results of animal studies indicate that repeated exposure to high levels of ozone for several months or more can produce permanent structural damage in the lungs. Among those most at risk to ozone are people who are outdoors and moderately exercising during the summer months. This includes construction workers and other outdoor workers.
Ground-level ozone interferes with the ability of plants to produce and store food, so that growth, reproduction and overall plant health are compromised. By weakening sensitive vegetation, ozone makes plants more susceptible to disease, pests, and environmental stresses. Ground-level ozone has been shown to reduce agricultural yields for many economically important crops (e.g., soybeans, kidney beans, wheat, cotton). The effects of ground-level ozone on long-lived species such as trees are believed to add up over many years so that whole forests or ecosystems can be affected. For example, ozone can adversely impact ecological functions such as water movement, mineral nutrient cycling, and habitats for various animal and plant species. Ground-level ozone can kill or damage leaves so that they fall off the plants too soon or become spotted or brown. These effects can significantly decrease the natural beauty of an area, such as in national parks and recreation areas. One of the key components of ozone, nitrogen oxides, contributes to fish kills and algae blooms in sensitive waterways, such as the Chesapeake Bay.
EPA's new ozone standards will provide increased protection beyond that provided by the previous standard from the following effects: Reduced risk of significant decreases (15% to over 20%) in children's lung functions (such as difficulty in breathing or shortness of breath), approximately 1 million fewer incidences each year, which can limit a healthy child's activities or result in increased medication use, or medical treatment, for children with asthma; Reduced risk of moderate to severe respiratory symptoms in children, hundreds of thousands of fewer incidences each year of symptoms such as aggravated coughing and difficult or painful breathing; Reduced risk of hospital admissions and emergency room visits for respiratory causes, thousands fewer admissions and visits for individuals with asthma; Reduced risks of more frequent childhood illnesses and more subtle effects such as repeated inflammation of the lung, impairment of the lung's natural defense mechanisms, increased susceptibility to respiratory infection, and irreversible changes in lung structure. Such risks can lead to chronic respiratory illnesses such as emphysema and chronic bronchitis later in life and/or premature aging of the lungs; Reduce the yield loss of major agricultural crops, such as soybeans and wheat, and commercial forests by almost $500,000,000.
Ozone is not emitted directly into the air, but is formed by gases called nitrogen oxides (NOx) and volatile organic compounds (VOCs) that in the presence of heat and sunlight react to form ozone. Ground-level ozone forms readily in the atmosphere, usually during hot weather. NOx is emitted from motor vehicles, power plants and other sources of combustion. VOCs are emitted from a variety of sources, including motor vehicles, chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. Changing weather patterns contribute to yearly differences in ozone concentrations from city to city. Also, ozone and the pollutants that cause ozone can be carried to an area from pollution sources located hundreds of miles upwind.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standards for ozone.
Air Quality Classifications for the 8-hour Ozone Standard
The CAA contains two sets of provisions--subpart 1 and subpart 2-- that address planning and control requirements for nonattainment areas. (Both are found in title I, part D.) Subpart 1 (which is referred to as "basic") nonattainment contains general, less prescriptive, requirements for nonattainment areas for any pollutant--including ozone--governed by a NAAQS. Subpart 2 sets forth a classification scheme for ozone nonattainment areas and provides more specific requirements for ozone nonattainment areas. (For more information on the subpart 2 classification and requirements see State Implementation Plans; General Preamble for the Implementation of Title I of the CAA Amendments of 1990; Proposed Rule.'' April 16, 1992 (57 FR 13498 at 13501 and 13510).) Some areas will be subject only to the provisions of subpart 1. Other areas will be subject to the provisions of subpart 2. Section 172(a)(1) provides that EPA has the discretion to classify areas subject only to subpart 1. Under subpart 2, areas are classified based on each area's ozone design value. Control requirements depend on an area's subpart 2 classification. Areas with more serious ozone pollution are subject to more prescribed requirements and are given longer to attain the standard. The requirements are designed to bring areas into attainment by their specified attainment dates.
Under EPA's 8-hour ozone implementation rule, published on April 30, 2004, (Volume 69, Number 84, Page 23951-24000) an area will be classified under subpart 2 based on its 8-hour design value if it has a 1-hour design value at or above 0.121 ppm (the lowest 1-hour design value in Table 1 of subpart 2). For the 1-hour ozone NAAQS, design value is defined at 40 CFR 51.900(c). For the 8-hour ozone NAAQS, design value is defined at 40 CFR 51.900(d). All other 8-hour ozone nonattainment areas will be covered under subpart 1. Section 172(a)(1) provides EPA with discretion whether to classify areas under subpart 1 and EPA is not classifying subpart 1 areas, with one exception. As noted in EPA's final rule on implementing the 8-hour ozone standard (Phase 1 implementation rule), EPA is creating an overwhelming transport classification that will be available to subpart 1 areas that demonstrate they are affected by overwhelming transport of ozone and its precursors and demonstrate they meet the definition of a rural transport area in section 182(h). No subpart 1 areas have been classified as of this date; however, for informational purposes, 8- hour ozone nonattainment areas covered under subpart 1 are identified as such in the classification column in 40 CFR part 81.
In the Phase 2 implementation rule, EPA will address the control obligations that apply to areas under both subpart 1 and subpart 2. Subpart 2 areas are classified as marginal, moderate, serious, or severe based on the area's 8-hour design value calculated using the most recent 3 years of data. At this time, there are no areas with design values in the extreme or severe 15 classification for the 8-hour ozone standard. As described in the Phase 1 implementation rule, since Table 1 is based on 1-hour design values, EPA promulgated in that rule a regulation translating the thresholds in Table 1 of section 181 from 1-hour values to 8-hour values. (See Table 1, below, ``Classification for 8-Hour NAAQS'' from 40 CFR 51.903.)
Table 1.--Classification for 8-Hour Ozone NAAQS
---------------------------------------------------------------
Maximum period for
Attainment dates in
8-hour design State plans (years
Area class value ppm after effective date of
(ppm ozone) nonattainment
designation for 8-hour
NAAQS)
--------------------------------------------------------
Marginal.... from...... 0.085 3
up to*.... 0.092
Moderate.... from...... 0.092 6
up to*.... 0.107
Serious..... from...... 0.107 9
up to*.... 0.120
Severe-15... from...... 0.120 15
up to*.... 0.127
Severe-17... from...... 0.127 17
up to*.... 0.187
Extreme..... equal to 0.187 20
or above
--------------------------------------------------------
*But not including.
Carbon monoxide (CO) is a colorless, odorless and poisonous gas produced by incomplete burning of carbon in fuels. When CO enters the bloodstream, it reduces the delivery of oxygen to the body's organs and tissues. Health threats are most serious for those who suffer from cardiovascular disease, particularly those with angina or peripheral vascular disease. Exposure to elevated CO levels can cause impairment of visual perception, manual dexterity, learning ability and performance of complex tasks.
77% of the nationwide CO emissions are from transportation sources. The largest emissions contribution comes from highway motor vehicles. Thus, the focus of CO monitoring has been on traffic oriented sites in urban areas where the main source of CO is motor vehicle exhaust. Other major CO sources are wood-burning stoves, incinerators and industrial sources.
The National Ambient Air Quality Standard for carbon monoxide is 9 ppm 8-hour nonoverlapping average not to be exceeded more than once per year. The rounding convention in the standard specifies that values of 9.5 ppm, or greater, are counted as exceeding the level of the standard. An area meets the carbon monoxide NAAQS if no more than one 8-hour value per year exceeds the threshold. (High values that occur within 8 hours of the first one are exempted. This is known as using "nonoverlapping averages.") To be in attainment, an area must meet the NAAQS for two consecutive years and carry out air quality monitoring during the entire time. Air quality carbon monoxide value is estimated using EPA guidance for calculating design values (Laxton Memorandum, June 18, 1990).
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standard for carbon monoxide.
Sections 107(d)(4)(A) and 186 of the Clean Air Act lists the requirements for designations and classifications of carbon monoxide areas.
Nitrogen dioxide (NO2) is a brownish, highly reactive gas that is present in all urban atmospheres. NO2 can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. Nitrogen oxides are an important precursor both to ozone (O3) and acid rain, and may affect both terrestrial and aquatic ecosystems. The major mechanism for the formation of NO2 in the atmosphere is the oxidation of the primary air pollutant nitric oxide (NO). NOx plays a major role, together with VOCs, in the atmospheric reactions that produce O3. NOx forms when fuel is burned at high temperatures. The two major emissions sources are transportation and stationary fuel combustion sources such as electric utility and industrial boilers.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standard for nitrogen dioxide.
High concentrations of sulfur dioxide (SO2) affect breathing and may aggravate existing respiratory and cardiovascular disease. Sensitive populations include asthmatics, individuals with bronchitis or emphysema, children and the elderly. SO2 is also a primary contributor to acid deposition, or acid rain, which causes acidification of lakes and streams and can damage trees, crops, historic buildings and statues. In addition, sulfur compounds in the air contribute to visibility impairment in large parts of the country. This is especially noticeable in national parks.
Ambient SO2 results largely from stationary sources such as coal and oil combustion, steel mills, refineries, pulp and paper mills and from nonferrous smelters. There are three NAAQS for SO2:
. an annual arithmetic mean of 0.03 ppm (80 ug/m3);
. a 24-hour level of 0.14 ppm (365 ug/m3); and
. a 3-hour level of 0.50 ppm (1300 ug/m3).
The first two standards are primary (health-related) standards, while the 3-hour NAAQS is a secondary (welfare-related) standard. The annual mean standard is not to be exceeded, while the short-term standards are not to be exceeded more than once per year.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standard for sulfur dioxide.
Air pollutants called particulate matter include dust, dirt, soot, smoke and liquid droplets directly emitted into the air by sources such as factories, power plants, cars, construction activity, fires and natural windblown dust. Particles formed in the atmosphere by condensation or the transformation of emitted gases such as SO2 and VOCs are also considered particulate matter.
Based on studies of human populations exposed to high concentrations of particles (sometimes in the presence of SO2) and laboratory studies of animals and humans, there are major effects of concern for human health. These include effects on breathing and respiratory symptoms, aggravation of existing respiratory and cardiovascular disease, alterations in the body's defense systems against foreign materials, damage to lung tissue, carcinogenesis and premature death. The major subgroups of the population that appear to be most sensitive to the effects of particulate matter include individuals with chronic obstructive pulmonary or cardiovascular disease or influenza, asthmatics, the elderly and children. Particulate matter also soils and damages materials, and is a major cause of visibility impairment in the United States.
Annual and 24-hour National Ambient Air Quality Standards (NAAQS) for particulate matter were first set in 1971. Total suspended particulate (TSP) was the first indicator used to represent suspended particles in the ambient air. Since July 1, 1987, however, EPA has used the indicator PM-10, which includes only those particles with aerodynamic diameter smaller than 10 micrometers. These smaller particles are likely responsible for most of the adverse health effects of particulate matter because of their ability to reach the thoracic or lower regions of the respiratory tract.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standard for particulate matter.
Exposure to lead (Pb) can occur through multiple pathways, including inhalation of air and ingestion of Pb in food, water, soil or dust. Excessive Pb exposure can cause seizures, mental retardation and/or behavioral disorders. A recent National Health and Nutrition Examination Survey reported a 78% decrease in blood lead levels from 12.8 to 2.8 ug/dL between 1976 and 1980 and from 1988 to 1991. This dramatic decline can be attributed to the reduction of leaded gasoline and to the removal of lead from soldered cans. Although this study shows great progress, infants and young children are especially susceptible to low doses of Pb, and this age group still shows the highest levels. Low doses of Pb can lead to central nervous system damage. Recent studies have also shown that Pb may be a factor in high blood pressure and in subsequent heart disease in middle-aged males.
Lead gasoline additives, non-ferrous smelters, and battery plants are the most significant contributors to atmospheric Pb emissions. In 1993 transportation sources contributed 33% of the annual emissions, down substantially from 81% in 1985. Total Pb emissions from all sources dropped from 20,100 tons in 1985 to 4,900 tons in 1993. The decrease in Pb emissions from highway vehicles accounts for essentially all of this decline. The reasons for the decrease are noted below.
Two air pollution control programs implemented by EPA before promulgation of the Pb standard in October 1978 have resulted in lower ambient Pb levels. First, regulations issued in the early 1970's required gradual reduction of the Pb content of all gasoline over a period of many years. The Pb content of the leaded gasoline pool was reduced from an average of 12.0 gram/gallon, to 0.5 gram/gallon on July 1, 1985, and still further to 0.1 gram/gallon on January 1, 1986. Second, as part of the EPA's overall automotive emission control program, unleaded gasoline was introduced in 1975 for automobiles equipped with catalytic control devices. These devices reduce emissions of CO, VOCs and NOx. In 1993, unleaded gasoline sales accounted for 99% of the total gasoline market. In contrast, the unleaded share of the gasoline market in 1984 was approximately 60%. These programs have essentially eliminated violations of the Pb standard in urban areas except those areas with Pb point sources.
Programs are also in place to control Pb emissions from stationary point sources. Lead emissions from stationary sources have been substantially reduced by control programs oriented toward attainment of the PM-10 and Pb ambient standards. However, significant and ambient problems still remain around some Pb point sources, which are now the focus of new monitoring initiatives. Pb emissions in 1993 from industrial sources, e.g., primary and secondary Pb smelters, dropped by about 91% from levels reported in 1970. Emissions of Pb from solid waste disposal are down about 76% since 1970. In 1993, emissions from solid waste disposal, industrial processes and transportation were: 500, 2,300 and 1,600 short tons, respectively. The overall effect of the control programs for these three categories has been a major reduction in the amount of Pb in the ambient air. Additional reduction in Pb are anticipated as a result of the Agency's Multimedia Lead Strategy issued in February 1991. The goal of the Lead Strategy is to reduce Pb exposures to the fullest extent practicable.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standard for lead.