Trees cleaning the air
Evergreen trees grow faster than most hardwood deciduous trees, so their absorption and oxygen emission is greater.
Note that trees do not &quot;clean&quot; air. Plants emit oxygen which is why air in a house with lots of plants will seem more fresh. In the global environment algae and other primitive organics are primarily responsible for converting CO2 to oxygen, not trees.
Particulate pollutants and some compounds with good water solubility, like sulfur dioxide and ammonia, are removed from air by moisture which condenses and falls to earth bringing the particulates with it.