Urban stormwater runoff contains nitrogen pollution that can harm water quality. A study analyzed stormwater samples from different urban areas to understand how nitrogen moves and where it comes from. They found that nitrogen levels were higher in roof runoff compared to road runoff and sewer flow. Road runoff was the main source of nitrate and particulate organic nitrogen in sewer flow. Coarse particles in stormwater mostly came from roads, while fine particles were from sewer sediments. This research suggests ways to manage nitrogen pollution in urban areas and improve stormwater quality.