The study analyzed how pollution from urban surfaces affects water quality in Beijing. Researchers monitored runoff from roofs and roads from 2004 to 2006. They found that both types of runoff were heavily polluted with COD and TN. Roof runoff exceeded pollution standards by 3.64 to 4.80 times, while road runoff exceeded by 3.73 to 1.07 times. The first flush effect, where initial runoff carries more pollutants, was more pronounced in roof runoff than road runoff. Factors like surface properties, rainfall intensity, and pollutant buildup influence the pollution levels in urban runoff.