Volatile organic compounds and nitrogen oxides , emitted from road transport and industrial processes, undergo chemical transformation in the atmosphere in the presence of sunlight to form ozone . Ozone, sulphur dioxide, and nitrogen dioxide primarily affect the respiratory systems of animals. Birds may be even more susceptible to gaseous pollutant injury than mammals due to their higher respiratory rates. Poor air quality can also affect vegetation. Sulphur dioxide , one of the main components of acid rain , has direct effects on vegetation.
Harm caused by sulphur dioxide is first noticeable on the leaves of the plants.
For some plants injury can occur within hours or days of being exposed to high levels of sulphur dioxide. Leaves in mid-growth are the most vulnerable, while the older and younger leaves are more resistant. Damage to coniferous needles can be seen in the extreme colour difference between the green base and the bright orange-red tips. Thus, even though sulphur dioxide levels may be extremely high, the levels may not affect vegetation because of the surrounding environmental conditions. It is also possible that the plants and soils may temporarily store pollutants.