As such, appropriate plant selection is a necessity. The atmosphere in many urban environments can contain excessive pollutants and dust. Pollutants include ozone, salts and many petrochemical by-products and will be absorbed by the plant via respiration. Dust, especially at construction sites, can accumulate upon plant leaves, clogging up stomatal openings, which interrupts the plant's normal transpiration and respiration patterns. The consolidation of people, structures, asphalt, vehicles and machinery within a congested urban environment has modified the climate conditions in many urban environments.
Temperatures are usually warmer within our cities versus outside the cities.
Two primary factors cause these warmer temperatures. First, atmospheric temperatures are raised by the heat and exhaust emitted by the huge numbers of machinery and vehicles. Second, sunlight shining upon the acres of parking lots, sidewalks, buildings and roads is reflected back into the atmosphere. Normally, when sunlight hits plant material or other soft matter it is absorbed. However, when the sunlight hits a hard, non-absorbing surface, the heat is reflected back into the environment, which causes a general rise in temperatures.