Yesterday, EPA formalized its decision to leave the ozone 
NAAQS unchanged, at 70 ppb. I don’t think that this decision is in the same category of egregiousness as EPA’s recent decision not to reduce the PM2.5 NAAQS. After all, only one decision can be the single worst environmental policy of an entire administration.
I’m not that close to the science on the ozone NAAQS,… More
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.… More