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National Ambient Air Quality Standards (NAAQS)

The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to set NAAQS for pollutants considered harmful to public health and the environment. The EPA has established NAAQS for six principal ("criteria") pollutants. These pollutants are: Carbon Monoxide (CO), Lead (Pb), Ozone (O3), Sulfur Dioxide (SO2), Particulate Matter (PM10 and PM2.5), and Nitrogen Dioxide (NO2). More information can be found at:

The CAA established two types of NAAQS, known as the primary and secondary standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

The CAA requires that the EPA reevaluate these standards every 5 years. Historically, this review has either not occurred at this interval or the EPA has chosen not to revise the NAAQS. However, recent litigation and court-order deadlines have caused the EPA to review the NAAQS on a schedule that more closely follows the 5 year cycle. The EPA relies on the Clean Air Scientific Advisory Committee (CASAC) to provide independent advice to the EPA Administrator on the technical bases for the NAAQS. More information can be found at:

Once established by the EPA, states have the primary responsibility for ensuring attainment (or compliance) of the NAAQS. Under the CAA, each state must develop a plan describing how it will attain and maintain the NAAQS. This plan is called the State Implementation Plan (SIP). More information can be found at:

Once a new/revised NAAQS is promulgated, the EPA designates all areas in each state as either unclassifiable, attainment, or nonattainment. The state has one year to recommend area designations to the EPA and the EPA has 2 years from promulgation of the final standard to complete the designation process, though they may be allowed an additional year if necessary.

With each new or revised NAAQS, the state has to provide a SIP amendment. Infrastructure SIPs are the general plans that each state must submit for implementing, maintaining, and enforcing any new/revised NAAQS. A nonattainment plan is the specific plan designed to address a particular area in the state that has been designated as nonattainment for a standard. Once nonattainment designations take effect, the state must develop a nonattainment SIP revision outlining how a particular area will attain and maintain the standards by reducing air pollutant emissions in that area. More information can be found at:

Several CAA elements are required for nonattainment plans. These elements, which can be burdensome, include: transportation conformity, nonattainment New Source Review, offsets, and additional controls aimed at bringing the area back to attainment. More information can be found at:



Ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOX), and volatile organic compounds (VOC) in the presence of sunlight. Formation of ground-level ozone is usually greatest during the summer when sunlight is stronger and temperatures are high. In South Carolina, levels are highest between April and October, and the ozone season runs from April 1 to October 31. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC. Volatile organic compound emissions also occur from natural sources, such as forests, grasslands, and swamps. Because so many VOCs occur naturally in the southeast, the better approach to reducing ground-level ozone has been to reduce NOx emissions.

Exposure to ozone can inflame and damage the lining of the lungs; reduce lung function; aggravate chronic lung diseases such as asthma, emphysema and bronchitis; and increase the frequency of asthma attacks. Ozone can also reduce forest growth, crop yields, and visibly damage the leaves of trees and other plants.

The EPA usually establishes a primary ozone standard to protect human health and a secondary ozone standard to protect plants, agriculture, and ecosystems. Compliance with these standards is determined by averaging the fourth highest annual 8-hour reading over three consecutive years. This number, called a design value, is compared to the current standards established by the EPA. As of March 29, 2011, the primary and secondary standards were both 0.075 parts per million (ppm). If the design value at a monitor in an area exceeds a standard, then the area is noncompliant and can be designated "nonattainment" for that standard.

More information about ozone can be found at: and


In 1990, the Clean Air Act (CAA) was amended and a focus was made to reduce ozone pollution across the country. The CAA amendments of 1990 identified a classification scheme for designating ozone nonattainment areas based on the severity of its ozone pollution and identified prescriptive requirements to help areas "attain" and "maintain" the ozone NAAQS.

In November 1991, Cherokee County, SC was designated nonattainment for the EPA's 1-hour ozone standard of 0.12 ppm, which was set in 1979. In December 1992, Cherokee County was redesignated attainment because the monitor in the area had a design value that met the standard. Cherokee County is now considered a maintenance area. A maintenance area is an area that was once nonattaining but has been redesignated attainment. SCDHEC has to develop a plan (maintenance plan) that explains how the area will continue to meet that standard. Cherokee County will be subject to a maintenance plan until 2014.

In 1997, the EPA established a new 8-hour ozone standard of 0.08 (effectively 0.084 due to rounding conventions). However, this standard was not fully implemented until 2004 due to litigation. In April 2004, three areas of the State were designated nonattainment for this standard: 1) Spartanburg, Greenville and Anderson Counties as one area; 2) parts of Lexington and Richland Counties as one area; and 3) the eastern third of York County along with the Charlotte metropolitan area as one area.

Because the Greenville, Spartanburg, and Anderson Counties area and the Richland and Lexington Counties area were meeting the 1-hour ozone standard at that time, the EPA allowed them to participate in the Early Action Compact program; deferring the nonattainment designation date and the requirements that accompany that designation to a later date. This gave the areas time to implement measures to improve their air quality. Under the EAC program, if the air quality in the areas participating in this program met the standards by December 31, 2007, the area would be redesignated attainment. The air quality in both of these areas improved, and they were redesignated attainment in April 2008.

Although the monitor in York County indicated that the air quality met the 2007 ozone standards, the EPA felt that the portion of the county along the I-77 corridor and the associated traffic contributed to the elevated ozone in the Charlotte, NC area. Therefore, the EPA included this portion of York County with the Charlotte nonattainment area (together referred to as the Metrolina nonattainment area). The portion of York County in the Metrolina nonattainment area was meeting the 1-hour ozone standard at that time. However, since the Charlotte area was not, the Metrolina nonattainment area was not allowed to participate in the EAC program.

In 2010, all of the monitors in the Metrolina nonattainment area produced design values below the 1997 ozone standard. Both South Carolina and North Carolina are currently preparing documentation for EPA to support the redesignation of this area to attainment. These requests, along with a maintenance plan that addresses how the State intends to keep air quality below the 1997 ozone standards, are expected to be submitted to the EPA by June 30, 2011. The EPA will have until December 2012 to make a decision on this request, and the Metrolina nonattainment area will be subject to maintenance plans until at least 2032.

In March 2008, the EPA finalized a new ozone standard of 0.075 ppm. In March 2009, SCDHEC, through the Governor's Office, recommended areas to the EPA that could be designated nonattainment. Currently, based on 2010 design values, only one monitor in our state (located in Spartanburg County) is exceeding 0.075 ppm. However, in January 2010, the EPA reopened the 2008 ozone standards for reconsideration, stating that it was going to consider an even more stringent primary standard between 0.060 and 0.070 ppm. The EPA has delayed the announcement of this standard three times, and an announcement is expected by July 29, 2011. If the EPA finalizes a standard within the range it is considering, much of the State could be designated nonattainment. The EPA has not yet promulgated any guidance regarding this reevaluation of the 2008 ozone standard.

The map below shows the location of the ozone monitors in South Carolina that have monitoring data used for comparison to the ozone NAAQS.

The graph below shows the downward trend in the design values at each monitor over the last decade. Note that air quality related to ozone has improved dramatically across the state.

Sulfur Dioxide NAAQS

Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as "oxides of sulfur." The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment.

Current scientific evidence links short-term exposures to SO2 (ranging from 5 minutes to 24 hours) with an array of adverse respiratory effects including bronchoconstriction and increased asthma symptoms. These effects are particularly important for asthmatics at elevated ventilation rates (e.g., while exercising or playing). Studies also show a connection between short-term exposure and increased visits to emergency departments and hospital admissions for respiratory illnesses, particularly in at-risk populations including children, the elderly, and asthmatics.

The EPA first set standards for SO2 in 1971. The EPA set a 24-hour primary standard at 140 parts per billion (ppb) and an annual average standard at 30 ppb to protect health. The EPA also set a 3-hour average secondary standard at 500 ppb to protect the public welfare. A review of the SO2 standards was completed in 1996 and the EPA chose not to revise them at that time.

On June 2, 2010, the EPA strengthened the primary standard for SO2 by establishing a new 1-hour standard at a level of 75 ppb. The EPA also revoked the previous two existing primary standards citing they will not add additional public health protection given the new standard.

Currently one monitor in the state (Irmo) is violating the new 1-hour SO2 standard with a value of 80 ppb (5 ppb over the standard). SCE&G's McMeekin facility is believed to be the primary contributor to observed concentrations at the Irmo monitor. The Bureau of Air Quality is currently developing a strategy with SCE&G to mitigate future exceedances via revised permit conditions.

Based on recently issued guidance, the SO2 standard area designations will eventually rely on modeled emissions from SO2 sources as well as monitoring. This is a significant departure from previous methods for determining violations of NAAQS which relied entirely on monitored concentrations. As such, SCDHEC will work to model SO2 sources to evaluate whether other areas should be categorized as "nonattainment" or "attainment" for the new standard. Until such a time, much of the state is expected to be designated as "unclassifiable" by the EPA.

More information on Sulfur Dioxide NAAQS can be found on the EPA's SO2 website at:

Particulate Matter NAAQS

Particulate Matter is the term used for solid and liquid particles in the air. These particles include acids, organic chemicals, metals, and soil or dust particles. Sources of particulate matter include power plants, industries, and automobiles. The EPA is particularly concerned about particles smaller than 10 micrometers (one millionth of a meter) in diameter, commonly called PM10, and particles smaller than 2.5 micrometers in diameter, commonly called PM2.5. PM10 and PM2.5 affect both the cardiovascular and respiratory systems. Children and older adults are most sensitive to particle pollution.

The EPA has regulated particle pollution since 1971, when it regulated particle pollution as "Total Suspended Particulate." This covered all sizes of airborne particles, including dirt and other larger particles. In 1987, the EPA changed the standard from Total Suspended Particulate to PM10, based on research that concluded that particles larger than 10 micrometers don't generally get past the nose and into the lungs. In 1997, the EPA added a standard for PM2.5, based on scientific evidence that particles of that size were particularly harmful. The EPA also added a daily and an annual standard for PM2.5. In 2006, the EPA strengthened the daily PM2.5 standard, retained the 1997 annual PM2.5 standard, and revoked the annual PM10 standard. The current 24-hour standard for PM10 is 150 micrograms per cubic meter (µg/m3). The current 24-hour standard for PM2.5 is 35µg/m3. The current annual standard for PM2.5 is 15 µg/m3.

SCDHEC currently operates 12 PM2.5 monitors and 10 PM10 monitors statewide, with no violation of the current PM2.5 or PM10 NAAQS.

The EPA plans to propose a revised PM NAAQS in summer 2011, and issue a final revised PM NAAQS in spring 2012. This rule may lower the current standards, add new standards for "inhalable coarse particles," particles between 2.5 and 10 micrometers across; and add a new secondary standard that protects visibility.

More information on the PM NAAQS can be found at:

Carbon Monoxide NAAQS

The Carbon Monoxide NAAQS is set at 9 parts per million (ppm), as an 8-hour average and 35 ppm, as a 1-hour average, neither to be exceeded more than once per year. The Carbon Monoxide NAAQS was initially established on April 30, 1971 and has recently been reviewed in a proposed rule retaining the current standards on February 11, 2011.

Carbon monoxide enters the bloodstream through the lungs and reduces the amount of oxygen delivered to the body's organs and tissue. The most serious health effect to people who suffer from cardiovascular disease is elevated carbon monoxide levels. Higher levels of carbon monoxide exposure can be poisonous and even healthy people may be affected. Visual impairment, reduced work capacity, reduced manual dexterity; poor learning ability and difficulty in performing complex tasks are all associated with exposure to high levels of carbon monoxide.

SCDHEC currently operates three carbon monoxide monitors statewide, with no violation of either form of the NAAQS.

More information on the CO NAAQS can be found at:


The Lead NAAQS is set at 0.15 µg/m3, maximum arithmetic 3-month mean concentration measured over a 3-year period. The Lead NAAQS was initially established on October 5, 1978, and last revised on October 15, 2008. On December 14, 2010, the EPA revised the ambient monitoring requirements for measuring lead in the air to better assess compliance with the NAAQS established in 2008. Based on the revisions to the lead monitoring requirements, SCHEC will be required to conduct sampling at any industrial facility with emissions greater than 0.5 tons per year of lead.

Lead exposure occurs mainly through inhalation of air and ingestion of lead in food, water, soil or dust. It accumulates in the blood, bones and soft tissues. It can also adversely affect the kidneys, liver, nervous system and other organs. Excessive exposure to lead may cause neurological impairments such as seizures, mental retardation, and behavioral disorders. Recent studies have shown that lead may be a factor in high blood pressure and subsequent heart disease. Lead can also be deposited on the leaves of vegetation, presenting a hazard to grazing animals.

SCDHEC currently operates four lead samplers statewide with no violation of the Lead NAAQS.

More information on the Lead NAAQS can be found on the EPA's website at:

Nitrogen Dioxide NAAQS

The Nitrogen Dioxide NAAQS is set at 100 ppb, annual 98th percentile 1-hour daily maximum concentration averaged over three years. The Nitrogen Dioxide NAAQS was initially established on April 30, 1971, and last revised on January 22, 2010 by the EPA. Recent revisions to the Nitrogen Dioxide NAAQS established a first time near-road monitoring network due to recent scientific studies into effects of pollution on populations living in close proximity to interstates and other major roads. This additional monitoring is expected to be in place by early 2013.

Short-term exposure (less than 3 hours) to low levels of nitrogen oxides may impede lung function in people with pre­existing respiratory illnesses and increases in respiratory illnesses in children between the ages of 5 and 12. Long-term exposure may lead to increased susceptibility to respiratory infections and may cause lung disease. Nitrogen oxides may also contribute to the aggravation of heart disease. Nitrogen oxides react in the air to form ground-level ozone and fine particle pollution, which are both associated with adverse health effects.

SCDHEC currently operates four nitrogen dioxide monitors statewide, with no violation of the Nitrogen Dioxide NAAQS.

More information on the Nitrogen Dioxide NAAQS can be found on the EPA's website at: