Last week, the Clean Air Scientific Advisory Committee formally transmitted its recommendations to EPA Administrator Regan regarding the PM2.5 NAAQS. Consistent with trade press reporting over the past few months, the majority of CASAC members recommended that the PM2.5 NAAQS be set between 8-10 ug/m3. A minority recommended the range be set between 10-11 ug/m3. I’d be surprised if the revised NAAQS is set above 10 ug/3. 
For me, what’s interesting about the letter is the suggestion that:
EPA should consider the implications of the exceptional events approach when applied to wildfires, particularly with respect to the risk assessment.
Apparently, that language was toned from draft language that more strongly suggested that EPA should change its exceptional events policy. Even so, it’s a pretty important issue. As the detailed CASAC comments note:
Exceptional events. EPA allows exclusion of wildfire PM events under the exceptional event rule when calculating PM2.5 design values. In some parts of the country wildfires are no longer “exceptional”. The dramatic increase in wildfires over the last decade is not natural; it is a combination of anthropogenic climate change, forest management practices, and power line ignition incidents. These are (in theory) at least partially controllable. Given the potential for significant adverse health events, it may be time to reconsider the current approach to excluding the high PM exposures from wildfire events in design values.
Should we really consider forest fires to be natural events? After all, Democrats think that the increase in wildfires is tied to human-caused climate change. Republicans blame Democratic forest management. Both explanations support the conclusion that many wildfires are not natural events.
At CASAC’s suggestion, I’ve considered the implications of the exceptional events approach and I think it’s time for a change.
Historically, EPA does treat wildfires as “natural events” covered by the exceptional events rule. Big question going forward, I think, is how to deal with prescribed fires (EPA has guidance on this for PM and ozone).
Whoops! Didn’t read the CASAC recommendation quote (my apologies). It’d be a stretch I think to consider wildfires as not “natural,” but perhaps there will be pressure on the agency to make the “not reasonably controllable or preventable” demonstration more rigorous for wildfire events. This could force states/land managers to be more proactive in light of climate change.
No worries. I think your second comment hit the nail on the head. Thanks.