What Are Hydrocarbons? What Are Photochemical Oxidants?

Hydrocarbons: Gasoline, methane, ethylene, butane, pentane, benzene, toluene, and propane are some examples of hydrocarbons. Incomplete combustion of fuels, motor vehicle exhaust, petroleum refineries, agricultural burning, manufacturing of explosives, and cracking of natural gas in petrochemical plants constitute the anthropogenic sources that emit hydrocarbons. In man, hydrocarbons bring about irritation of mucus membrane, bronchial constriction, and eye irritation. Some are carcinogenic as well.

Photochemical oxidants: In brown-air cities located in warm, dry and sunny climates, atmospheric hydrocarbons and nitrogen oxides from automobiles and power plants react in the presence of sunlight, forming a number of secondary pollutants, such as ozone, formaldehyde, peroxyacylnitrate (PAN), and many others. These reactions are called photochemical because they involve both sunlight and chemical pollutants. The resulting brownish orange shroud of air pollution is photochemical smog. In human beings, photochemical oxidants cause stinging of eyes, respiratory irritation, and emphysema i.e. general breakdown of lung alveoli, and there is difficulty in catching one's breath.