Bad air quality and running are just not a good mix. For big cities, areas near big cities in underdeveloped countries, or for those affected by things like forest fires and the drifting smoke from these events, regularly checking the AQI (air quality index – which measures 6 common pollutants and rates them on a scale 0-500) through your local weather channel or app is a must. Here is general ‘rule of thumb’ list for running in various air quality conditions.

AQI scale and running*

0-50 (green):	All systems good, all workout types are ok!
51-100 (yellow):	Generally ok for all workouts for all runners, save for those with chronic conditions or sensitive to pollution.
101-150 (orange):	For healthy runners without sensitivity or chronic conditions, best to stick to easy running only, or run indoors (where the windows and doors are always closed).
151-200 (red):	Best to not run outdoors, given the risk of long-term health of the lung and cardiovascular system. If you ‘have’ to run outdoors in these conditions, run easy and with a quality air mask.
201-300 (purple):	If you must be outdoors, walking with a mask is recommended, as any more intensity and the breathing rate and force increases, thus exposing your lungs to a higher density of pollutants. Though some runners will still go out and run in 201-300 conditions, and even some marathons have been held in this range, studies show performance suffers and respiratory/cardiovascular risk increases. Is it worth it?
301-500 (maroon):	No, it is not worth it.

Studies on AQI and its impact on runners have been taking place throughout the world, however much of the long-term health risks have not been fully deduced and validated with data. Common sense, though, will likely land in the same place as long-term studies – though some may be able to run in lesser quality air conditions and have little to no impact on their health, quality of life, and life expectancy, others will suffer lung or cardiovascular complications from such activities. You will not know which one you are until it is too late, so let’s let common sense keep us out of harm’s way.

* This list was derived from recommendations from the US Environmental Protection Agency and the American Lung Association.