Which pollutant category did trees show a significant ability to remove?

Trees are particularly effective at removing particulates from the air through a process known as deposition. This occurs when particles such as dust, smoke, and other small pollutants settle on the surfaces of leaves and bark or are trapped by foliage. The structure of tree leaves, which often have a rough texture, allows them to capture and hold onto these airborne particulates, improving air quality.

While trees can also absorb carbon dioxide during photosynthesis, the term "particulates" specifically refers to solid or liquid particles in the air, making it the most direct answer for pollutants that trees remove significantly. In contrast, carbon monoxide and carbon dioxide are gases and are dealt with through different mechanisms, primarily gas absorption rather than particulate deposition. Additionally, although trees can help reduce dust levels to some extent, "particulates" encompasses a broader range of airborne particles and is more accurate in this context.