Particulates pollutants are the minute solid particles or liquid droplets in air. These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries. There are two types of particulates present in the atmosphere :

$(a)$ Viable

$(b)$ Non-viable

$(a)$ Viable Particulates : The viable particulates like bacteria, fungi, moulds, algae etc. are

minute living organisms that are dispersed in the atmosphere. Human beings are allergic to some of the fungi found in air. They can also cause plant diseases.

$(b)$ Non-viable particulates : Non-viable particulates may be classified according to their nature and size as follows:

$(i)$ Smoke: Smoke particulates consist of solid or mixture of solid and liquid particles formed during combustion of organic matter. e.g., cigarette smoke, smoke from burning of fossil fuel, garbage and dry leaves, oil smoke etc.

$(ii)$ Dust : Dust is composed of fine solid particles. It produced during crushing, grinding and attribution of solid materials. e.g., sand from sand blasting, saw dust from wood works, pulverized coal, cement and fly ash from factories, dust storms etc.

$(iii)$ Mists : Mists are produced by particles of spray liquids and by condensation of vapours in air. e.g., sulphuric acid mist and herbicides and insecticides that miss their targets and travel through air and form mists.

$(iv)$ Fumes : Fumes are generally obtained by the condensation of vapours during sublimation, distillation, boiling and several other chemical reactions. e.g., organic solvents, metals and metallic oxides form fume particles.