Well, no. They aren't measuring PM, they're measuring opacity which is NOT well correlated with PM. It IS, however, what the public *****es about! I don't know if this is still the case but for many years the Federal emissions test required actual PM testing (done gravimetrically over the course of a transient emissions test on an engine dyno) and eventually an opacity test done as a separate testing sequence. There's all sorts of data to demonstrate that PM and opacity are barely acquainted with each other as every Diesel engine certification test for years had both PM values and opacity results.

Maricopa County is cheaping out so that it LOOKS like they're doing something when really they could get about the same result by shining a flashlight thru the plume! Send them to me if they want to do REAL testing - they wouldn't like what I have to tell them (takes about $2M minimum to even start getting set up to do meaningful testing).

Glad you passed.

Dan