It's not too cold now. Why is there steam in my car exhaust pipe?

First of all, you have to understand what gas it is, which is actually waste gas and water vapor. Usually you can't see it when the weather is hot. When the weather is cold, it is obvious that other vehicles with normal emissions can see water vapor, and the temperature of water vapor is relatively high. We can see that the temperature difference between water vapor and the outside is relatively large, so it will be visualized, but it is not obvious when the outside temperature is high. Of course, this has an important relationship with one of its components, namely the three-way catalytic converter. There is no water in automobile emissions, and the water vapor discharged from there is mainly nitrogen oxides, hydrocarbons, carbon monoxide, carbon dioxide and other gases, which will pollute the environment. So using a three-way catalyst to make these gases flow over the surface of his honeycomb to play a chemical role, separating hydrogen and oxygen from the gas, in fact, transforming nitrogen oxides and hydrocarbons. What is the composition of water in our junior middle school physics? Mainly oxygen and hydrogen, right? Therefore, when the ternary converter is converted, the more water vapor, the better. Plus the weather, so don't worry, it just means that your car has good emissions.