The billions of dollars spent on state-of-the-art sports facilities over the last quarter-century have made high-efficiency air filtration systems more common, thanks in part to the pursuit of green and healthy building certifications. Upgrades will likely increase in the post-coronavirus era, too.

The problem is that even the cleanest of air can’t keep this particular virus from spreading; if someone coughs or sneezes, those droplets are in the air. That means outdoor ballparks have high contaminant potential, too.

“Most of the real risk is going to be short-distance transmission, people sitting within two, three or four seats of each other,” said Ryan Demmer, an epidemiologist at the University of Minnesota’s School of Public Health. “It’s not really about the virus spreading up, getting into the ventilation system and then getting blown out to the entire stadium because this virus doesn’t seem to transmit that way. It doesn’t aerosolize that well.”