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2C H A P T E R 2 2.1 U.S. Standards for Airborne Lead Concentrations Concerns regarding adverse health effects associated with exposure to airborne lead resulted in lead being classified as an air pollutant pursuant to the Clean Air Act in 1976, followed by the requisite enactment of a health-based National Ambient Air Quality Standard (NAAQS) for lead by the EPA in 1978, which was set at 1.5 micrograms per cubic meter based on a measured quarterly-average concentration. In October 2008, the EPA promulgated a revised lead NAAQS that lowered the acceptable level by an order of magnitude, to 0.15 micrograms per cubic meter based on a rolling 3-month average concentration. In December 2014, the EPA issued a proposed rulemaking in which it reaffirmed its position that the existing lead NAAQS of 0.15 micrograms per cubic meter is set appropriately to protect public health (U.S. EPA 2015b). 2.2 Elimination of Lead from Gasoline Used in Cars and Trucks Concerns regarding ambient lead concentrations and the adoption of vehicle emission stan- dards necessitating the use of catalytic converters, which are poisoned by lead, resulted in the EPAâs promulgation of regulations requiring the phase-out of lead from gasoline used in on-road vehicles (which is known as motor gasoline or âMOGASâ) beginning in the mid-1970s. These regulations required major gasoline retailers to begin selling at least one grade of unleaded MOGAS by July 1, 1974 (U.S. EPA 2000b). Vehicle engines required redesign to accommodate the elimination of lead from gasoline, and special gasoline nozzle and vehicle fill-pipe designs were needed to prevent the introduction of lead-containing gasoline into vehicles designed for use with unleaded fuel. By 1988, the amount of lead consumed in MOGAS in the United States was reduced by 99 per- cent (U.S. EPA 2000a). Leaded MOGAS was completely phased out by 1990 in Canada and by 1996 in the United States. Although leaded gasoline continued to be used in racing applications in the United States, strictly speaking those are not on-road motor vehicles. As a result, in highly populated areas such as California, ambient lead levels dropped rapidly in the late 1970s and early 1980s as lead began to be eliminated from gasoline, as shown in Figure 1. Regulation of Airborne Lead in the United States
Regulation of Airborne Lead in the United States 3 Figure 1. Maximum 30-day average lead levels in California (1973â1998). Source: Sierra Research, Inc., CVS News, October 1993. 0 2 4 6 8 10 12 '75 '76 '77 '78 '79 '80 '81 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93 '94 '95 '96 '97 '98 A ir bo rn e Le ad (µ g/ m 3 ) Calendar Year Maximum 30-Day Average 3-Year Average
