to revise standards when necessary to protect the public health and the environment (EPA 1997). By the mid-1990s, scientific evidence suggested that the standards for both particulate matter (PM) and ozone needed revision. Accordingly, EPA proposed new PM and ozone NAAQS and released an RIA evaluating the benefits and costs of the proposed standards (EPA 1997). The proposed PM and ozone standards were evaluated in the same RIA because of the similarities in precursors, sources, atmospheric residence times, and atmospheric chemistry. The RIA also included an assessment of a proposed regional haze rule; however, the committee focused on the health benefits analyses conducted for the PM and ozone standards because they were more closely related to its task.

The proposed standards that were evaluated were (1) an annual mean PM2.5 standard of 15 micrograms per cubic meter (µg/m3) and a 98th percentile 24-hour (hr) average of 65 µg/m3 in conjunction with an annual mean PM10 standard of 50 µg/m3 and 99th percentile 24-hr average of 150 µg/m3, and (2) an 8-hr ozone standard of 0.08 parts per million (ppm) based on the fourth highest average daily maximum.1 Two alternative standards were also evaluated for PM2.5 and ozone. EPA evaluated a partial-attainment scenario that accounted for areas that would not be able to meet the proposed standards or alternatives based on current control technologies and a full-attainment scenario that assumed no residual nonattainment. EPA noted that more uncertainty was associated with the estimates for the full-attainment scenario because attainment was based on development of new technologies. The benefits were estimated in the year 2010 because EPA assumed that the majority of CAA-mandated controls would be achieved by that date.

EPA used a six-step approach for estimating the benefits for the proposed and alternative PM and ozone standards. In the first step, EPA developed an emissions inventory for the year 2010. The inventory included estimates for volatile organic compounds (VOCs), nitrogen oxides (NOx), sulfur dioxide (SO2), secondary organic aerosols, PM2.5, PM10, and ammonia (NH3). To construct the 2010 inventory, EPA first generated a 1990 emissions inventory using source-specific emissions factors and activity levels, such as fuel consumed by electric utilities or miles traveled by motor vehicles. The 2010 emissions inventory was then projected using the 1990

1  

PM10 refers to PM with an aerodynamic diameter of 10 µm or less, and PM2.5 refers to PM with an aerodynamic diameter of 2.5 µm or less.



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