The rainwater runoff from roofs in central Beijing is polluted with nitrogen, ammonia, and solids, exceeding environmental standards. Rainwater is less polluted but still exceeds standards at times. The first flush of pollutants in rainwater runoff is moderate, with ammonia and solids being the most prevalent. Pollutant levels in roof runoff are linked to rainfall length and intensity. Vehicle emissions contribute nitrogen to rainwater, while roofing materials and metal pipes release solids, organics, and phosphorus into roof runoff.