Air pollution has increased by urbanization and industrialization. Rural areas are being converted to urban areas continuously and unplanned industrialization is taking place. This leads to felling of large number of trees, as these are needed for construction and manufacture of paper etc. In general, there is a natural rate at which trees grow. If the rate, at which trees grow, is lesser than the rate at which they are cut down, the numbers of trees are bound to decrease slowly. Trees give out enormous amount of water by transpiration. This helps in formation of rain-clouds. When the forests get depleted, the rainfall in the area is reduced. This causes in even lesser number of trees that results in soil erosion and the area become a desert.
Fumes and gases from factories pollute the air. Acidic gaseous oxides liberated by the chimneys of the factories cause acid rain. Acid rain causes soil and water pollution and damages historical monument. Sound (loud voice or noise) produced by machines in factories causes sound pollution. Hot water liberated by many factories affects life under water and cause water pollution. Thus, urbanization and industrialization have leads to various types of pollution. Air pollution can be checked by enforcing strict laws against the polluters.