The evidence of the harm resulting from PM2.5 exposures keeps rolling in. Earlier this month, Environmental Research published an article titled “Global mortality from outdoor fine particle pollution generated by fossil fuel combustion: Results from GEOS-Chem” (abstract available; full article requires purchase), which concluded that global annual mortality from PM2.5 exposure is roughly twice as high as previously estimated. 
Somehow, I don’t think that this is going to persuade those who believe that a causal relationship between PM2.5 levels below the current NAAQS and increased mortality has not been established, but I do expect the evidence to continue to pile up – and I don’t have any doubt that a decision by EPA to reduce the PM2.5 NAAQS would easily stand up to judicial review, even before our most conservative judges.
And I continue to have a vision of a really green future, when we’ve attained a pretty much carbon-free electricity grid in order to address climate change. We’re then going to see how much “co-benefits” really do matter. Asthma rates will have decreased. Mortality related to PM2.5 exposure will have decreased.
There is reason to be optimistic.