Looking at the air quality index is showing numbers in the red- over 150 and thus considered unhealthy. In fact, as I look, there’s an air quality alert issued by the national weather service (on behalf of Montana DEQ apparently).
Unhealthy, not just for sensitive groups, means that everyone ought to be limiting strenuous outdoor activity, and those in sensitive groups (kids, the elderly, those with respiratory illnesses, etc.) should avoid it entirely.
Why reduce activity? Because the amount of particles you’re taking into your lungs is dependent on a few factors: Amount of particles in the air, Length of Exposure, Rate of Breathing
Thus, longer and more strenuous activity increases the exposure to potential toxins in the air. Wildfire smoke is a potent mix of toxins: carbon monoxide, hazardous air pollutants, polycyclic aromatic hydrocarbons, and particles. The particles are actually some of the more dangerous components- the smallest of them can actually travel from the lungs directly into the bloodstream.
Where is all the smoke coming from anyway? Check out the Fire and Smoke Map. It doesn’t just show the air quality reports, it also shows smoke plumes and active fires. Interested in more particulars about the air quality- Today’s Air is a good source, though most weather sites seem to be providing that information now as well.