Sometimes, I’m alone—in rhythm with only my breath and my thoughts. Other times, I’m with a friend, sharing stories and jokes as our strides fall in step with one another. In either case, this time is sacred. I’m a runner, and for me, there’s nothing better than a crisp morning, when the air is fresh, the sun is peaking over the horizon, and my legs are light.

But some days, when the smog is thick and my phone buzzes with an air quality warning, I know running outdoors will be unpleasant—and unsafe. When this happens, I worry that we’ll reach the point of no return—a day pollution holds us hostage not once or twice a summer, but every day of the year.

That doesn’t