If one is living in a polluted city and plants trees around their house, Will it reduce air pollution? What about reducing heat in the summer?
Trees (and plants for that matter) can reduce air pollution by trapping small particles (fine dust) on their leaves and by absorbing gases such as nitrogen dioxide, ozone and sulfur dioxide. However, depending on the location and type of tree it is also possible that trees prevent pollution like exhaust fumes from cars from flowing away quickly. Also, to have any noticeable effects you would have to plant a lot of trees and/or plant big already-mature trees.
Air quality improvement in New York City due to pollution removal by trees during daytime of the in-leaf season averaged 0.47% for particulate matter, 0.45% for ozone, 0.43% for sulfur dioxide, 0.30% for nitrogen dioxide, and 0.002% for carbon monoxide .... Large healthy trees greater than 77 cm in diameter remove approximately 70 times more air pollution annually (1.4 kg/yr) than small healthy trees less than 8 cm in diameter (0.02 kg/yr). (source)
HeatA single tree can have a fairly big influence on heat. Bricks, roofing and tiles take up a lot of heat when they are in direct sunlight, so making sure they are shaded by trees can help keep things cooler. Also, the transpiration of a tree also has a cooling effect by keeping the air more moist.
All the trees show a consistent effect: temperatures are reduced and humidities are elevated under the canopies. The greatest cooling effect (0.7 -1.3°C) occurs in the early afternoon. ... However, street trees are significantly less effective in cooling than either individual trees or clumps planted over grass. (source)