The resulting stresses have a definite effect upon the plants we grow. Crowded conditions exist, especially in urban areas, with serious pollution of the air, water, and even soil. The environment in city gardens may also be particularly abnormal because of unique situations that occur there. Thus, it's easy to see how the walls of buildings in close proximity can cause rapid changes in air circulation. Plants growing in such places are quickly damaged, particularly those receiving full sunlight.
Air pollution can be very distressing, for the damage to many ornamentals is often serious.
Furthermore, the symptoms may be mistaken for those caused by diseases or insects. Pollution problems are covered in detail by another chapter in this book. Sources of air pollution are many. They include factories and power plants, vehicle engines, refuse burning, heating plants and home heating units, and forest fires. But there are many others.