Today, in our environmental science lecture, we'll discuss the impact of urban green spaces on air quality. A recent study in London found that planting trees along busy roads can reduce particulate matter by up to 30%, but only if the trees are spaced correctly. However, the effect is limited when buildings are too tall, as they trap pollutants. Interestingly, green roofs are less effective for street-level pollution but help with building insulation. Therefore, city planners should prioritize street trees in open areas, not just parks.