Urban road runoff contains harmful pollutants like dirt, chemicals, and metals that can harm water quality. To reduce pollution and protect water bodies, researchers studied 207 samples from storm events in Xi'an. They found that the runoff was mainly polluted by dirt and chemicals, with high levels of metals like lead and chromium. The amount of pollutants in the runoff changed depending on the rainfall and the type of pollutants. Dissolved pollutants peaked early in the runoff, while dirt pollutants peaked later with heavy rainfall. Different types of rainfall affected the amount of pollutants washed away, with some types causing more pollution than others.