Why Can We See Our Breath on a Cold Day?
When you exhale when it’s cold outside, the water vapor in your breath condenses into lots of tiny droplets of liquid water and ice (solid water) that you can see in the air as a cloud, similar to fog. When it’s warm out, though, the invisible water vapor gas stays invisible, because the warm air provides energy that allows the water vapor to remain a gas. As temperatures drop, it’s more likely that you’ll be able to see your breath.
It’s just science at work. The small cloud that our breath forms on a cold day comes from the water vapor we breathe out. Water vapor is water that has evaporated into a gas. There is always some water vapor in the air we breathe in, and the body adds even more. The lining of the nose and throat makes the air moist and warm. Our lungs add more water vapor. When we exhale this moist air into the cold outdoor air, our breath suddenly cools.
Some of the water vapor that we breathe out turns to water droplets that form a steamy cloud. This is called condensation. There’s no exact temperature at which condensation will occur. Many environmental factors other than temperature can play a role in condensation, including relative humidity (the amount of moisture in the air). When it falls below 45° F, though, you can usually expect to be able to see your breath.