Seems like too few categories, safe or not safe? Clearly this is a spectrum
Categorical thinking is not always because of a lack of nuance or of zealotry or stupidity (which are generally more modern dismissive interpretations). Delineating categories is a useful framing to firmly separate what is on the one hand good and virtuous (clean air), and on the other evil and depraved (polluted air). It's an excellent way to identify when exactly rationalization, submission or complaisance kicks in. Well, it's not as bad as it used to be. It's even worse in xyz country. It's not reflected in the average life expectancy. It's the price we pay for modern luxuries etc... etc... Having firm categories, and these will read as fearful or callous defenses.
Good categories should compel to action. In this case, what can be done to move from Box B into Box A. And then do those things (because Box B is inherently evil).
The real world is grey. For sure. And multiple opposing things can be true at once. Nonetheless, we need to cut through that, and I'm fearful we've forgotten how. The reason our cities are degraded is in large part because we have failed to think in categories, and have rationalized away (categorically) wrong habits.
With domestic violence it is trivially easy to have none at all, and there is a very distinct difference between none and some.
With air quality there is a smooth and continuous measurement for what is in the air. You will never get to zero particulates per cubic meter, you can only get under a certain level. Further, the effects of air quality are also a smooth continuous function - there isn't some distinct point where if you are below it there's no risk of health issues and immediately above it you have guaranteed serious health issues. A binary categorization is clearly inappropriate.
So while not binary, the difference between dangerous and not is usually pretty sharp.
For PM 2.5, < 12 ug/m3 is considered safe, while > 35 ug/m3 is considered harmful after just few hours. For chronic exposure, mean levels of < 15 ug/m3 over 3 years is considered safe. (There is probably some level that is certain to produce silicosis in about everyone. I would have to dig on that.) That is how thin the margin is. And these are the laxer NIOSH values.
Even AQI which is weighted to be more linear and granular, easily gets pegged at moderate (risky to sensitive people) in clean seeming cities unless there's wind... (That is a level above 15 ug/m3 already by some.)
Note that the idea of a single safe “threshold” limit is based on the best available research today showing that they haven’t measured adverse health effects below 5 μg/m³ average annual exposure. The spectrum here is a spread of increased mortality that can be attributed to pollution above that limit. There’s a different threshold for a single day exposure than for average exposure. Also note that the recommendation recently came down from the 2005 recommendation of 10 μg/m³ due to more research showing adverse health effects of pollution. There might not exist any so-called “safe” limit, and speculating wildly, we might expect their recommendation to drop again in the future.
That's not to say the obvious is not true, that Regions of China and India suffer from too much PM2.5 due to human activity and should be addressed. However, a chicken little situation is not helpful as people will tune out.
Edit: Downvotes but no comments. That's a pretty low effort way of admitting your position is faith-based, not scientific.
If any of these measures is "in the red", your air is unhealthy.
Why not?
There are lots of people and groups out there for which this is the goal.