Every runner has stood in a doorway, looked at a hazy sky, and wondered whether “kind of smoky out” is a real reason to skip a run or just an excuse dressed up in health concerns. The honest answer depends entirely on the actual AQI number, and most people never check it.
A slow recovery jog and a hard interval session expose your lungs to very different volumes of air. During intense exercise, breathing rate can climb 10–20x above resting levels, and a lot of that air bypasses your nose’s filtering and goes straight in through the mouth. That means the same AQI reading is a bigger deal for a threshold workout than for an easy shakeout run — worth factoring in before you cancel or push through.
AQI 90 and a hard interval session is a very different exposure than AQI 90 and an easy recovery jog, even though the air outside hasn’t changed at all.
AQI is a composite score, but the pollutant driving it changes what precautions actually help. Wildfire smoke is mostly fine particulate matter (PM2.5), which a well-fitted N95 genuinely filters. Ground-level ozone, common on hot, sunny, stagnant afternoons, is a gas that a cloth or surgical mask does essentially nothing against — the only real mitigation is timing (run earlier, before ozone builds through the day) or moving indoors.
Don’t treat “the air looks a little hazy” as a vibe-based decision. Check the actual number, factor in how hard you’re planning to work, and know that a mask helps against smoke but does nothing against ozone. Above 150, most people should genuinely move the workout indoors — that’s not caution for its own sake, that’s the number telling you something real.