Air pollution short notes civil engineering

AIR POLLUTION | CIVIL ENGINEERING NOTES PART - 01

(Air pollution short notes civil engineering)

INTRODUCTION

Air pollution is the presence of one or more air contaminants such as dust, fumes, gas, mist, odour, smoke, or vapours, in such a quantity or duration that may be injurious to plants and animals.

NATURAL CONTAMINANTS

Some types of natural contaminants are discussed below -

1. Aerosols :

   1. The particles which are larger than a molecule but small enough to remain suspended in air are called aerosols.

   2. The particulate matter may occur in air largely in solid form as particles of dust, smoke, fume etc.

   3. The particulate matter that exists in the liquid form is known as mist and fog.

2. Dust :

   1. Dust is made up of small, solid particles created by the breakup of larger masses through processes such as crushing, grinding, or blasting that may come directly from the processing or handling of materials such as coal, cement, limestone or grains.

   2. It may be a by-product of mechanical processes such as the sawing of wood, or made up of residue of mechanical processes such as the sawing of wood , or made up of residue of mechanical operations such as sand blasting.

   3. Dust may range in size from 1 to 1000 𝛍m and are capable of temporary suspension in air or other gases. Dust does not diffuse, they settle under the influence of gravity.

3. Smoke :

   1. Smoke consists of fine, solid particles resulting from the incomplete combustion of organic particles such as coal, wood or tobacco.

   2. And it consists mainly of carbon and combustible materials.

   3. Smoke particles have diameters ranging from 0.5 to 1 𝛍m which is smaller than dust particles.

4. Fumes :

   1. They are fine solid particles that are often metallic oxides in nature such as zinc and lead oxides formed by the condensation of vapour of solid materials.

   2. Fumes may be from sublimation, distillation, calcination or molten metal processes.

   3. They range in size from 0.03 to 0.3 𝛍m, fumes usually flocculate and coalesce before settling down.

5. Fly ash :

   1. They consist of finely divided, non-combustible particles contained in flux gases arising from the combustion of coal.

   2. These mineral or metallic substances are released when the organic portion of coal is burned.

   3. Like dust particles as discussed before, their size ranges from 1 to 1000 𝛍m.

6. Mist :

   1. Mist consists of liquid particles or droplets formed by the condensation of vapour.

   2. Mist are usually less than 10 𝛍m in diameter.

   3. And if mist concentration is high enough to obstruct visibility, the mist is called fog.

7. Spray :

   1. It consists of liquid particles formed by the automization of parent liquids, such as pesticides and herbicides.

   2. Spray particles ranges in size from 10 to 1000 𝛍m

PRIMARY POLLUTANTS

The atmosphere, as a matter of fact, contains hundreds of air pollutants from natural or from anthropogenic sources (i.e, domestic and industrial wastewater effluents, urban and agricultural runoff, fossil fuel combustion or any pollutants made by humans etc.), all such pollutants are called primary pollutants.

Examples of primary pollutants are -

• Sulphur dioxide gases

• Carbon Monoxide gases

• Nitrogen oxides NO and NO2

• Lead (Pb)

• Hydrocarbons

• Allergic agents like pollens and spores

• Radioactive substances etc.

And other less significant primary pollutants include H2S, H2F and other fluorides, methyl and ethyl mercaptan etc.

SECONDARY POLLUTANTS

The primary pollutants often react with one another or with water vapour, in the presence of sunlight, to form a set of new pollutants, called secondary pollutants.

Examples of secondary pollutants are-

• H2SO4 (More toxic than SO2 gases)

• Ozone (O3)

• Formaldehyde

• Peroxl-acetyl-nitrate (PAN)

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For SSC-JE Civil Engineering preparation, you can refer to the previous notes by Sandeep Jyani, and the notes provided here is a summarized note from the exam point of view which are ready-made for all the serious aspirants.

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