The freezing point of urea solution is 20 degrees. Urea can't be used as snow melting agent because of ammonia volatilization, and it is more expensive than sodium chloride.

First of all, urea only affects the emission of nitrogen oxides from automobiles, so it will not reduce the power output of automobiles. Secondly, there is a temperature sensor in the urea pump. When the sensor detects that the urea temperature is below 7 degrees Celsius, the urea pump will stop working. The main purpose of this is to prevent urea crystallization from blocking the urea system.

The national standard urea solution freezes below-1 1℃. If the urea concentration is high, its freezing point will be relatively reduced. We must use urea solution with standard concentration of 32.5. Excessive concentration of urea solution will lead to a large number of precipitates in urea solution, which will easily lead to blockage of urea pump. If the concentration is too low, the expected purification effect can not be achieved, and the annual inspection is easy to fail.