Hydrocarbon (HC):

Hydrocarbons such as methane, ethylene, acetylene is present in air. Most of these are low molecular weight gases and liquids at ordinary temperature.

Source:

(i)     Coal fields, natural fires.

(ii)   Incomplete combustion from car engines.

(iii) Industrial sources.

(iv) Agricultural burning.

(v)   Anaerobic decomposition of organic matter in soil.

               Organic matter  CH₄  + CO₂

Sinks:  hydrocarbons undergo a number of chemical reactions and photochemical reactions through a number and form water and CO₂ at the end.

               Hydrocarbon      H₂O + CO₂

Effects:

(i)     At high conc. Hydrocarbons have carcinogenic effect on lungs.

(ii)   Inhalation of benzene, toluene etc causes irritation in mucus membrane.

(iii) Responsible for the photo chemical smog.

(iv) Methane causes narcotic effects on human beings.

Control:

1.      Hydrocarbons tend to get oxidized in the atmosphere by series of chemical and photochemical reactions. This results in the formation of CO2, solid organic particulate and waste soluble gases. Solid particulate settles down and gases dissolve in water to soluble acids which washed down by rain.

2.      Hydrocarbons from vehicular traffic are controlled by the technique such as incineration, adsorption and absorption.

3.      Installation of a connection system in automobile reduces loss of hydrocarbons by evaporation from fuel tanks and carburetor.