Last week, EPA posted its draft Integrated Science Assessment for Particulate
Matter. It's the foundational document for EPA's
periodic review of its National Ambient Air Quality Standard for
PM. The current standard for PM2.5, promulgated in 2012,
is 12 ug/m3.
Section 109 of the Clean Air Act requires the Administrator to
set the NAAQS "requisite to protect the public health"
with "an adequate margin of safety."
The new ISA states that:
Evidence from U.S. studies examining short-term PM2.5 exposure
and mortality indicate a linear relationship at concentrations as
low as 5 µg/m3 with cut-point analyses providing
no evidence of a threshold.
There is some uncertainty in the discussion in the ISA, but it
seems pretty clear to me that the current standard of 12
ug/m3 does not protect the public health with an
adequate margin of safety.
