The fires in NSW have a lot of people buying particulate masks even though none of them are rated for air as bad as we have. They all say “do not use when pollutants exceed 10 times the safe limit” which is 20-50μg/m³ depending on whose limits you use. Not that is matters, 1000μg/m³ is more than 10x any of the safe limits.
I like the look of the “smoggie” unit, but I’d quite like CO2 as well, assuming we can sort out the calibration problems with that measure. But either way I suspect my cowokers will be buying one to put outside at work.