When wildfire smoke is in the air, doctors urge people to stay indoors. But what happens to trees and other plants that can’t escape? They may respond a bit like us, it turns out: Some trees essentially shut their windows and doors and hold their breath. As atmospheric and chemical scientists, we study the air quality and ecological effects of wildfire smoke and other pollutants. In a study that started quite by accident when smoke overwhelmed our research site in Colorado, we were able to watch how the leaves of living pine trees responded. …What our data told us is that some plants respond to heavy bouts of wildfire smoke by shutting down their exchange with outside air. …Smoke particles could coat the leaves. …Smoke could also enter the leaves and clog their pores. …Or the leaves could physically respond to the first signs of smoke. …It’s likely a combination of these and other responses.