Today, in our environmental science lecture, we'll discuss the impact of urban green spaces. Recent studies show that parks and community gardens can reduce city temperatures by up to 2 degrees Celsius during summer. Additionally, they improve air quality by absorbing pollutants. However, the benefits depend on the size and distribution of these areas. For instance, small scattered gardens are less effective than one large central park. Interestingly, green roofs on buildings also contribute, but their cooling effect is minimal compared to ground-level parks. Now, what is the key factor for maximum benefit?