Today in our environmental science lecture, we'll discuss the impact of urban green spaces on air quality. A recent study in Melbourne monitored two parks over a year. The researchers found that trees, especially broad-leaved species like oaks, reduced particulate matter by up to 30% near busy roads. However, the effect was only significant within 50 meters of the green area. Interestingly, the study also noted that grass areas had a minimal effect compared to tree canopies. The lead researcher, Dr. Emily Watson, suggests that city planners should prioritize planting clusters of trees rather than isolated ones to maximize air purification benefits.