system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When it's really cold out, why can you see the exhaust from cars, but only until they warm up?
gpt
What is happening when you can see the exhaust is that warm water vapor is cooling and collecting into small droplets that are suspended in the air around them. When the exhaust system is cool the water starts condensing before it leaves the pipes. Once everyting is warmed up though the exhaust stays hot enough that by the time it has cooled enough for the water vapor to condense it is too dispersed into the atmosphere to form enough droplets to become opaque.