Which intervention is effective for reducing urban air pollution?

Promoting public transportation is an effective intervention for reducing urban air pollution because it encourages a shift away from individual car use, which contributes significantly to vehicle emissions. By increasing the accessibility and use of public transit systems, cities can decrease the number of cars on the road, leading to lower overall emissions of pollutants such as nitrogen oxides, particulate matter, and carbon dioxide. Additionally, public transportation options like buses and subways can be designed to run on cleaner energy sources, further reducing their environmental impact.

The other options do not effectively address air pollution concerns. Increasing the number of vehicles would likely exacerbate the problem by raising traffic congestion and emissions. Limiting the height of buildings does not directly impact air pollution levels, as it does not address the primary sources of emissions. Reducing green spaces can further worsen air quality, as vegetation plays a crucial role in absorbing carbon dioxide and other pollutants, thus helping to purify the air.