There is an air quality measuring site at Enumclaw (yes I know, King County) that does measure near the base of Rainier.
And that one station, plus the other rural north bend station, almost always say the air is perfectly clean. The stations near Seattle are used to determine king county bans.
It's cool though, there have been noticeably less burn bans in recent years. I'm hoping it is a lasting trend. Maybe because of more natural gas availability, newer appliance conversion, lazy millennial homeowners, cleaner cars, etc.