On October 16, 2008, EPA Administrator Stephen Johnson announced his final approval of a more stringent National Ambient Air Quality Standard (NAAQS) for lead. The publication of the revised standard in the Federal Register , on November 12, 2008, was the final step in a multi-year review process. When the previous standard for lead was promulgated in 1978, lead was a widespread air pollutant. Eighty to ninety percent of it was emitted by the nation's automobiles and trucks, a majority of which ran on leaded gasoline. Leaded gasoline was gradually phased out in the 1970s, 1980s, and early 1990s, and both emissions and concentrations of lead in the air plummeted. Emissions fell more than 98% from 1980 to 2007. Ambient concentrations (the quantity of lead in the air) fell by 94%. As of March 12, 2008, only two areas with a combined population of 4,664 people had air that remained in violation of the 1978 lead NAAQS. These developments led some to suggest that there was no longer a need for an ambient air quality standard for lead. Others, including the independent scientific advisory panel that advises EPA's Administrator, concluded that the 1978 NAAQS was far too lenient, that lead in ambient air still poses a threat to public health, and that the NAAQS needed to be significantly strengthened as the result of the recent review. In promulgating a new standard, the Administrator agreed with his scientific advisers, lowering the standard to 90% below the 1978 standard and setting new requirements for monitoring. This report provides background on NAAQS, the process used to establish them, the factors leading to the reduction in lead emissions, the proposed and final changes to the lead standard and related monitoring requirements, as well as information regarding the potential effects of the revision. NAAQS are standards that apply to ambient (outdoor) air pollutants that exhibit two characteristics: (1) they may reasonably be anticipated to endanger public health or welfare; and (2) their presence in the air results from numerous or diverse mobile or stationary sources. The Clean Air Act provides for two types of NAAQS: primary standards, "the attainment and maintenance of which in the judgment of the [EPA] Administrator ... are requisite to protect the public health," with "an adequate margin of safety"; and secondary standards, necessary to protect public welfare, a broad term that includes damage to crops, vegetation, property, building materials, etc. NAAQS are at the core of the Clean Air Act, even though they do not directly regulate emissions. In essence, they are standards that define what EPA considers to be clean air. Once a NAAQS has been set, EPA uses monitoring data and other information submitted by the states to identify areas that exceed the standard and must, therefore, reduce pollutant concentrations to achieve it. After these "nonattainment" areas are identified (which EPA estimates will occur by January 2012 at the latest for the new lead standard), state and local governments must produce State Implementation Plans outlining the measures they will implement to reduce pollution levels and attain the standards. Lead nonattainment areas will have five years after their designation to actually attain the standard, with a possible extension of five more years. As will be noted in more detail later, most areas of the country do not monitor lead concentrations in ambient air. Thus, in addition to strengthening the lead standard, the Administrator expanded the requirements for lead monitoring. Installing the additional monitors and compiling up to three years of data to determine compliance is the main reason that implementing the new standard is likely to be a lengthy process. In addition to requiring states to submit implementation plans, EPA also acts to control many of the NAAQS pollutants wherever they are emitted, through national standards for products that might emit them (particularly fuels) and through emission standards for new stationary sources (e.g., lead smelters). The Clean Air Act requires the agency to review each NAAQS every five years. That schedule is rarely met, but it often triggers lawsuits that force the agency to undertake a review. In the case of lead, the last review of the NAAQS was completed in 1978. The Missouri Coalition for the Environment and others filed suit against EPA over its failure to complete a review in 2004, and a consent decree established the schedule EPA followed in reviewing the standard. The schedule required EPA to propose any revision of the standard by May 1, 2008, and to promulgate a final decision by October 15, 2008. Reviewing an existing NAAQS is a long process. As a first step, EPA scientists review the scientific literature published since the last NAAQS revision, and summarize it in a report known as a Criteria Document or Integrated Science Assessment. Generally, there are hundreds or thousands of scientific documents reviewed, covering such subjects as environmental concentrations, human exposure, toxicology, animal studies and animal-to-human extrapolation, epidemiology, effects on vegetation and ecosystems, and effects on man-made materials. A second document that EPA prepares, the Staff Paper or Policy Assessment, summarizes the information compiled in the Criteria Document and provides the Administrator with options regarding the indicators, averaging times, statistical form, and numerical level (concentration) of the NAAQS. To ensure that these reviews meet the highest scientific standards, the 1977 amendments to the Clean Air Act required the Administrator to appoint an independent Clean Air Scientific Advisory Committee (CASAC). CASAC has seven members, largely from academia and from private research institutions. In conducting NAAQS reviews, their expertise is supplemented by panels of the nation's leading experts on the health and environmental effects of the specific pollutant or pollutants under review. These panels can be quite large. The 2005-2008 lead review panel had 15 members, in addition to the 7 statutory members of CASAC. CASAC and the public make suggestions regarding the membership of the panels on specific pollutants, with the final selections made by EPA. The panels review the agency's work during NAAQS-setting and NAAQS-revision, rather than conducting their own independent reviews. The pollutants to which NAAQS apply are generally referred to as "criteria" pollutants. Six pollutants are currently identified as criteria pollutants: ozone, particulates, carbon monoxide, sulfur dioxide, nitrogen oxides, and lead. The EPA Administrator can add to this list if she determines that additional pollutants meet the act's criteria (endangerment of public health or welfare, and numerous or diverse sources); she can delete them if she concludes that they no longer do so. Whether lead still met these criteria was one of the issues EPA considered in its review of the standard. The reduction of lead emissions is often described as one of the key successes of the Clean Air Act and of the Environmental Protection Agency. In 1970, emissions of lead totaled 224,100 tons. By 2007, emissions had been reduced more than 99%, to 1,300 tons. Little of that success is attributable to the setting of a NAAQS, however. The agency did not set a NAAQS for lead until 1978 (by which time lead emissions had already declined about 40%), and it established the NAAQS then only as a result of a lawsuit filed by the Natural Resources Defense Council and others. After promulgating the NAAQS, the agency did not identify nonattainment areas until 1991. The great bulk of the lead reductions "occurred prior to 1990," according to EPA. So, in general, the reduction of lead in ambient air did not come about as a result of the 1978 NAAQS, or in the manner prescribed by Title I of the Clean Air Act, wherein nonattainment areas are identified and the states or areas in which they are located submit to EPA State Implementation Plans that identify local and national measures that will be implemented to help such areas reach attainment. Most of the reduction was a side-benefit of other Clean Air Act programs, especially the regulation of emissions from new automobiles, beginning in the 1970s. In order to meet more stringent requirements for emissions of hydrocarbons, nitrogen oxides, and carbon monoxide, which took effect in 1975, the auto industry installed catalytic converters on new cars. Gasoline with lead additives would have fouled the catalytic converters, rendering them useless; so, in anticipation of the converters' widespread adoption, EPA mandated the sale of unleaded fuel in the early 1970s, and eventually banned the use of lead in gasoline entirely. Being a metal, lead remains in the environment even though emissions have declined. Thus, although human exposure to lead has declined, it has not done so by as much as the decrease in emissions would suggest. Furthermore, research conducted since the 1970s suggests that lead has significant health impacts at levels well below those previously considered safe. Current sources of emissions include utility and other boilers, leaded fuel still used in some general aviation airplanes, trace lead contaminants in diesel fuel and gasoline, lubricating oil, iron and steel foundries, primary and secondary lead smelters, hazardous waste incinerators, and about 30 smaller categories of sources. In addition, there continues to be exposure from lead particles in soil or dust re-suspended in the atmosphere as a result of vehicular traffic, construction, agricultural operations, and the wind. As a result of the review it completed in 2008, EPA decided to deal with the remaining issue of lead in ambient air by both strengthening the lead NAAQS and by expanding the network of monitors that are used to measure attainment. The primary (health-based) standard, promulgated in 1978, was 1.5 micrograms per cubic meter (µg/m 3 ) averaged over three months. With the exception of two small areas (one in Montana, one in Missouri), the United States has attained this standard, but the NAAQS review found evidence of health effects at the levels of exposure currently experienced by much of the U.S. population.