The number to watch is 100, because CDC's heat-and-air-quality guidance says an Air Quality Index above 100 means outdoor air is unhealthy for sensitive groups, while 51 to 100 can still affect some sensitive people. [1]

That makes AQI a practical threshold, not a mood, since a child with asthma, an older runner, a pregnant person, or someone with heart or lung disease does not need a culture-war thread about smoke or ozone so much as a decision about recess, soccer practice, yard work, or a long commute on foot.

CDC's companion guidance describes AQI from 0 to 100 as generally satisfactory and 101 to 500 as unhealthy, with the day's value set by the pollutant with the highest concentration, and it warns against a common mistake: AQI does not include pollen, so a low AQI does not mean the allergy day is easy. [1] [2]

The divergence is familiar: mainstream weather turns the index into color blocks, X turns it into institutional distrust or dismissal, and the useful middle is behavioral, with sensitive groups altering outdoor activity over 100 while some people under 100 still listen to symptoms.

The same rule helps schools and coaches because it does not require everyone indoors at the first hint of haze, but it does require adults to know which children have asthma, which workouts can move inside, and which outdoor plans are optional when the index crosses from information into risk.

-- NORA WHITFIELD, Chicago