Comments on EPA’s Proposed Rule, National Ambient Air Quality Standards for

EPA has proposed lowering the level of the National Ambient Air Quality Standard
(NAAQS) for PM2.5. Under EPA’s proposal, the 24-hour PM2.5 standard would be
lowered from 65 micrograms per cubic meter (µg/m3) down to 35 µg/m3, while keeping
the annual standard at its current level of 15 µg/m3. If adopted, the proposed standard
would double the fraction of PM2.5 monitors that violate federal PM2.5 standards,
resulting in a substantial increase in both the stringency of federal PM2.5 standards and
the difficulty of achieving regional PM2.5 attainment.

Based on pressure from EPA’s Clean Air Scientific Advisory Committee (CASAC) and
from environmental groups and newspaper editorial boards, EPA will presumably also
consider adopting a 24-hour and/or annual standard of even greater stringency than the
current proposed rule. Instead, EPA should scrap its proposed rule to lower the PM2.5
NAAQS and should keep the PM2.5 NAAQS at their current levels.

As demonstrated in this comment letter, and contrary to EPA’s and CASAC’s claims, the
current NAAQS already protect public health “with an adequate margin of safety,” as
required by the Clean Air Act (CAA). Indeed, standards even less stringent than the
current PM2.5 NAAQS would also protect public health.