be especially important contributors to O₃ pollution (via the emissions of VOC) and PM. In recognition of their importance, states first began working together to develop rules to control VOC emissions from some types of area sources in the late 1980s. For example, California and other states began adopting product formulation requirements for low-VOC architectural coatings. These were eventually translated into national requirements in the 1990 CAA Amendments, which contained several provisions requiring EPA to identify and regulate area sources of such products. A major impediment to making progress on area-source emissions arises from the large number of uncertainties associated with emission inventories for these sources. Specific challenges include the many sources in any given category and the wide variation in the conditions and operating practices under which the emissions can occur. To address the problem, the Emission Inventory Improvement Program (EIIP) includes the development of inventories for area sources (EPA 2001b), but it is unclear, barring a more ambitious program of measuring and testing, whether such an inventory-development process will result in a more accurate understanding of the contribution of area sources to air pollution in the United States.

Section 183(e) of the 1990 CAA Amendments required EPA to conduct a study of consumer and commercial products by 1993 to identify products that needed regulation and then to proceed with developing control technology guidelines (CTGs) for each priority category. EPA completed the study in 1995, identifying four groups of consumer and commercial products, including such items as aerosol spray paints, architectural coatings, and industrial cleaning solvents. EPA proceeded with developing CTGs for the categories of products within those groups, albeit slowly. Regulations for the first group were scheduled to be in place by 1997, and regulations for all four groups were to be completed by 2003 (64 Fed. Reg. 13422 [1997]). Currently, however, only three of the six product categories within the first group have been regulated; no regulations for the other three groups (scheduled for completion 1999, 2001, and 2003) have been completed. EPA noted in its 1999 Federal Register notice (64 Fed. Reg. 13422) that it “intends to exercise discretion in scheduling its actions under section 183(e) in order to achieve an effective regulatory program.” The slow pace appears to be due to the perception that such rules are not central to efforts to attain the NAAQS for O₃. However, in the absence of high-quality inventories and the contributions of these sources to pollution, it is difficult to verify whether the perception is accurate.

Title III of the 1990 CAA Amendments also requires EPA to list and regulate area sources of HAPs. In some cases, MACT standards have been developed for several categories of area sources, including commercial dry cleaning, hazardous waste incineration, secondary aluminum production, and secondary lead smelting. The amendments also required EPA to address