	Introduction

On October 16, 2008, EPA Administrator Stephen Johnson announced his final approval of a more stringent National Ambient Air Quality Standard (NAAQS) for lead. Leaded gasoline was gradually phased out in the 1970s, 1980s, and early 1990s, and both emissions and concentrations of lead in the air plummeted. 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. Thus, in addition to strengthening the lead standard, the Administrator expanded the requirements for lead monitoring. Lead Emission Reduction: Success, but Not Generally Due to NAAQS

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. 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. The Primary Standard

The primary (health-based) standard, promulgated in 1978, was 1.5 micrograms per cubic meter (µg/m 3 ) averaged over three months. CASAC concurred, stating in a January 22, 2008 letter that it "... unanimously affirms EPA staff's recognition of the need to substantially lower the level of the primary NAAQS for Lead, to an upper bound of no higher than 0.2 µg/m 3 ...."
The Administrator agreed that the primary NAAQS should be substantially lowered, choosing a level of 0.15 µg/m 3 . The Secondary Standard

As part of its current review, EPA also assessed the secondary (public welfare) NAAQS for lead. Twenty-four entire states, including some with major sources of lead emissions, had no lead monitors. The agency also proposed to require a small network of monitors to be placed in urban areas with populations greater than one million to gather information on the general population's exposure to lead in the air. In the final rule, the Administrator chose thresholds different than proposed: he set the source threshold at one ton of emissions rather than 200-600 kilograms, and required monitors in urban areas with populations of 500,000 or more rather than one million. The monitoring decision was challenged by the Natural Resources Defense Council, Missouri Coalition for the Environment Foundation, and two other groups: they petitioned the agency for reconsideration of the monitoring requirements, in January 2009. EPA agreed to a reconsideration in July and proposed changes to the monitoring rule on December 23. The agency also proposed eliminating the required monitoring in areas with populations of 500,000 or more, in favor of a network of approximately 80 multi-pollutant monitoring sites known as NCore. Rather than support the deletion of lead from the list of criteria pollutants, they concluded that lead in ambient air still poses a threat to public health, that the old NAAQS (established in 1978) was far too lenient, and that the 1978 NAAQS needed to be significantly strengthened. Given uncertainties in the science (particularly the estimated correlation between airborne lead and blood lead levels and the uncertainties in the concentration-response functions—i.e., the effect that changes in blood lead levels have on IQ), the Administrator stated in the May 2008 proposal that his decision would be supported by the science at any point in the proposed range of 0.10 to 0.30 µg/m 3 .
The Administrator of the Environmental Protection Agency (EPA), under a court order to review the National Ambient Air Quality Standard (NAAQS) for lead, announced his decision October 16, 2008, reducing the standard by 90%, from 1.5 micrograms per cubic meter (µg/m3) to 0.15 µg/m3. EPA also promulgated new monitoring requirements at that time, requiring monitors downwind of any source emitting one ton or more of lead per year and in urban areas with populations of 500,000 or more. In January 2009, the Natural Resources Defense Council and three other groups petitioned EPA for a reconsideration of the monitoring requirements. EPA granted the petition and, in December 2009, proposed changes in the monitoring requirements, notably lowering the source-oriented emissions threshold from one ton to 0.50 tons per year.
NAAQS are standards for outdoor (ambient) air that are intended to protect public health and welfare from harmful concentrations of pollution. In strengthening the lead standard, the Administrator has concluded that protecting public health and welfare requires much lower concentrations of lead pollution in ambient air than the level previously held to be safe. Lead particles can be inhaled or ingested, and, once in the body, can cause lower IQ and effects on learning, memory, and behavior in children. In adults, lead exposure is linked to increased blood pressure, cardiovascular disease, and decreased kidney function.
Regulation of airborne lead is often described as one of the key successes of the Clean Air Act and of the Environmental Protection Agency. In 1970, when lead was widely used as a gasoline additive, emissions of lead nationwide totaled 224,100 tons. Lead was also present then in many consumer products, and thus was emitted to the air from industrial processes and waste incinerators. The phasing out of lead from gasoline, paint, and other products, as well as stricter controls on industrial emissions, reduced lead emissions more than 99%, to 1,300 tons in 2007.
The reduction in lead emissions and ambient concentrations led some to suggest that there was no longer a need for an ambient air quality standard for lead. Others, including the Clean Air Scientific Advisory Committee (CASAC), an independent panel of scientists who advise the EPA Administrator, concluded that the old NAAQS (established in 1978) 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. CASAC recommended that the standard be reduced from 1.5 µg/m3 to no higher than 0.2 µg/m3. In promulgating a more stringent NAAQS, the Administrator agreed with the scientists' recommendation, rejecting the argument that the standard is no longer needed.
The Administrator's decision followed a multi-year review of the science. To implement the new standard, EPA and the states will first identify nonattainment areas (expected to occur no later than January 2012), following which there will be a 5-10 year-long implementation process in which states and local governments will identify and implement measures to reduce lead in the air. As noted earlier, EPA also promulgated changes to the monitoring requirements for lead as part of the NAAQS decision. As of 2008, at least 24 of the 50 states, including some with major sources of lead emissions, had no lead monitors at all. Under the 2008 regulations, all 101 metropolitan areas with populations greater than 500,000 would be required to have monitors as would the estimated 135 areas that have sources of lead emissions greater than or equal to one ton per year. In December 2009, EPA proposed further changes, lowering the source-oriented emissions threshold from one ton to 0.50 tons per year, while eliminating the urban area monitoring requirement. In place of the latter, lead monitoring would be added to a national network of 80 sites that will monitor multiple pollutants.