There are different levels of air quality. You can find a list of all the different air quality levels and what they represent:
Excellent (0 to 5 μg/m³ of PM2.5)
There is no risk to your health.
Very Good (5.1 to 12 μg/m³ of PM2.5)
Air quality is very good, with little to no risk to your health. No precautionary actions are needed.
Moderate (12.1 to 22 μg/m³ of PM2.5)
Consider limiting exertion on your ride if you have any underlying health conditions.
Poor (22.1 to 35 μg/m³ of PM2.5)
Those in at-risk health groups should consider limiting heavy or prolonged exertion.
Very Poor (35.1 to 75 μg/m³ of PM2.5)
Older people, children, and those with respiratory or heart disease should limit prolonged or heavy exertion.
Unhealthy (75.1 μg/m³ of PM2.5 or more)
Everyone should limit prolonged or heavy exertion.