Today in our environmental science lecture, we'll discuss urban green spaces. Recent studies show that parks in cities not only reduce air pollution but also lower local temperatures by up to 3 degrees Celsius. Interestingly, the cooling effect is strongest within 100 meters of the park boundary. However, the size of the park matters less than the density of trees. For example, a small park with dense canopy can be more effective than a large open lawn. Additionally, green roofs on buildings contribute to cooling, but they are less effective for street-level pedestrians compared to street trees.