Question

(a) How do oxides of nitrogen enter the atmosphere ?

(b) What are their harmful effects ?

Answer 1

(a)

Nitric oxide (NO) and nitrogen dioxide (NO₂) enter the atmosphere in the following ways:

1. On burning of fuels in furnaces, temperature increases. At high temperature, nitrogen and oxygen present in air combine to form oxides of nitrogen.
2. When fuel burns in an internal combustion engine, oxides of nitrogen are produced, and they enter the atmosphere as exhaust gases from automobile engines.
3. Nitric acid is formed by the reaction between atmospheric nitrogen and oxygen in the presence of electric discharge, which occurs during thunderstorms when there is lightning.
4. Nitric oxide further reacts with atmospheric oxygen and ozone to form nitrogen dioxide.

(b)
Harmful effects of the oxide of nitrogen

• Nitrogen dioxide is very harmful to plants and animals.
• It causes irritation in the mucous membrane.
• Large concentrations of NO₂ may cause serious lung diseases.
• Nitrogen dioxide causes serious injury to vegetation; it damages plant leaves.
• In sunlight, nitrogen dioxide oxidises hydrocarbons to form photochemical smog. Photochemical smog causes eye irritation, asthma attacks and nasal and throat infections.