Urea aqueous solution is urea solution with stable concentration (composed of 32.5% high-purity urea and 67.5% deionized water), which is used to reduce nitrogen and oxygen compounds in automobile exhaust after combustion. Common fertilizer urea contains biuret, mechanical impurities, formaldehyde and high content of metal ions, which will cause catalyst poisoning of SCR aftergas processor and damage of urea pump and other components. If irreparable damage occurs, it will be a great loss for users.

In addition, because urea is easy to crystallize at low temperature and the concentration of urea aqueous solution cannot be guaranteed, the conversion rate of nitrogen oxides will be low. In addition, the loss of ammonia gas can damage the SCR system, making the vehicle unable to meet emissions standards.

Nitric acid produced by NOx combined with water in the air is a major cause of acid rain. At the same time, NOx and other pollutants will produce photochemical smog pollution under the action of ultraviolet light. It is very harmful to the atmosphere and has a great impact on human health. Therefore, the behavior of adding water to replace urea aqueous solution should be denied and resisted.

Too high or too low concentration can not improve the conversion efficiency of nitrogen oxides, but will cause the residual ammonia to form secondary pollution. The 32.5% concentration was chosen because the crystallization point of urea aqueous solution at this concentration was lower (freezing point -11℃).

Because urea water solution is easy to be polluted by impurities or exposed to the sun after opening algae, and urea itself decomposition to produce ammonia loss, so that the solution volatilization caused the deterioration of urea, so it is better to store urea water solution according to the requirements of businesses in summer.