Trees play a significant role in removing air pollutants. They absorb gaseous pollutants like carbon monoxide (CO), nitrogen dioxide (NO2), and ozone (O3) through their stomata and leaf surfaces.

 Trees play a significant role in removing air pollutants. They absorb gaseous pollutants like carbon monoxide (CO), nitrogen dioxide (NO2), and ozone (O3) through their stomata and leaf surfaces. Additionally, trees intercept and trap airborne particles, including particulate matter (PM), effectively reducing their concentrations in the air. 

Here's a more detailed look at how trees remove air pollutants:

1. Gaseous Pollutant Absorption:

Stomata Uptake: Trees have tiny pores called stomata on their leaves that allow them to absorb gaseous pollutants like CO, NO2, and O3.

Leaf Surface Absorption: Some gaseous pollutants can also be absorbed directly by the leaf surface.

Internal Reactions: Once inside the leaf, these gases can be absorbed by water films or react with internal leaf surfaces, effectively converting them into less harmful substances. 

2. Particulate Matter Removal:

Interception and Trapping:

The leaves and branches of trees intercept airborne particulate matter, acting as a physical barrier to these pollutants.

Deposition and Retention:

Some particles are deposited on the leaf surface, while others are temporarily retained on the plant surface.

Washing and Resuspension:

Rain can wash away deposited particles, while some particles may be resuspended back into the air. 

3. Indirect Benefits:

Temperature Reduction:

Trees provide shade, which can lower ambient temperatures, indirectly reducing the formation of ozone, a harmful air pollutant.

Reduced Energy Consumption:

Shaded buildings require less air conditioning, leading to lower energy consumption and emissions. 

4. Factors Affecting Removal Capacity:

Tree Species:

Different tree species have varying pollutant removal capacities. 

Canopy Structure:

Dense tree canopies are more effective at intercepting and removing pollutants. 

Pollutant Concentrations:

Higher pollutant concentrations in the air can lead to increased removal by trees. 

Meteorological Conditions:

Weather conditions, such as wind and precipitation, can affect the removal process. 

5. Quantifying the Benefits:

Estimates of Pollutant Removal:

Studies have estimated the amount of air pollutants removed by urban trees, with varying results depending on the location and species. 

Economic and Health Benefits:

The air pollution removal by trees has a monetary value, and it also leads to improved human health by reducing exposure to pollutants. 

Mitigation of Growth:

Urban vegetation can also mitigate the growth of air pollutant concentrations.