L-5Units of measurement Units of measurement

and definitionsand definitions

Air Pollution and Control

(Elective-I)

Contents of unit-II

•• LL--4 4 Classification of Classification of pollutants pollutants Quantity Quantity and and composition composition of particulate of particulate & & gaseous pollutantgaseous pollutant..

•• UUnits nits of of measurement (measurement (Already Already covered).covered).

Other way of classifying air pollutants

No. Group Examples

1 Sulphur compounds SO2, SO3, H2S,Mercaptans

2 Nitrogen compounds NO, NO2, NH3

3 Oxygen compounds O3, CO, CO2

4 Halogen compounds HF, HCl

5 Organic compounds Aldehydes, hydrocarbons

6 Radioactive compounds

Radioactive gases

Natural Contaminants

Pollen is important natural contaminant because of its peculiar properties of irritation and allergy sometimes leading to bronchitis, asthma and dermatitis.

Pollen grains are discharged into the atmosphere from plants etc. The air transported pollen grains range mainly between 10 and 50 microns.

Aerosols

• Aerosols: Aerosols refer to thedispersion of solid or liquid particles ofmicroscopic size in the air. It can also bedefined as a colloidal system in whichthe dispersion medium is gas and thedispersed phase is solid or liquid.

• The diameter of the aerosol may rangefrom 0.01 (or less) micron to 100 micron.The various aerosols are as follows:-

Smoke

• Smoke consists of finely divided particles produced by incomplete combustion

• Size- less than 1 micron

• Coal smoke – 0.2 to 0.01 micron

• Oil smoke – 1.0 to 0.03 micron

Mists

• This term refers to a low concentration dispersion of liquid particles of large size.

• Size- 500 to 40 micron

Fog

• Fog refers to visible aerosols in which dispersed medium is liquid.

• Formation by condensation is usually implied.

• Reduces visibility

• Size- 40 to 1.0 micron

Fumes

• These are solid particlesgenerated by condensation fromgaseous state, generally aftervolatilization from meltedsurfaces and oftenaccompanied by a chemicalreaction such as oxidation.

• Size varies from 0.1 to 1 micron

SOURCES OF ATMOSPHERIC DUST

No. Sources Examples

1 Combustion Fuel burning (Coal, wood, fuel oil)Incineration/burning (house and municipal garbage)

2 Material handling and processing

Loading and unloading (sand, gravel, coal, ores, lime, cement)Crushing and grinding (ores, stone, cement, rocks, chemicals)Food processing (Flour, corn starch, grains)Cutting and forming (saw mills, wall boards, plastics)Metallurgical (Foundries and smelters)Industrial (Paper, textile manufacture etc. )

No. Sources Examples

3 Earth moving operations

Construction (roads, buildings, dams, sites clearance)Agricultural (soil filling, land operations)Mining (Blasting)

4 Miscellaneous

House cleaningMud road cleaningCrop sprayingPoultry feedingEngine exhaust

GasesGases

• Following are the main air pollutant gases

((ii) Sulphur dioxide: ) Sulphur dioxide: It is a major air

pollutant gas produced by the combustion of fuels like coal. The main source of electricity production is by burning of fossil fuels in India and the whole world. The sulphur content of the coal varies from 1 to 4% and fortunately the Indian coal is low in sulphur content. SO2 is also produced in the metallurgical operations.

(ii)Oxides of nitrogen: (ii)Oxides of nitrogen: Oxides of

nitrogen are produced either in the production of nitric acid or in the automobile exhausts and as the effluent of power plants. Out of the seven oxides of Nitrogen (N2O, NO, NO2, NO3, N2O3, N2O4, N2O5) only nitric oxide and nitrogen dioxide are classified as the main pollutants. All the oxides of nitrogen are collectively known as NOX.

(iii) Carbon monoxide: (iii) Carbon monoxide: It is

produced because of the incomplete combustion of coal and other petroleum products. It is produced in the exhaust of automobiles. In the pollution check of vehicles mainly CO and unburnt hydrocarbons are measured.

(iv) Hydrogen sulphide: (iv) Hydrogen sulphide: Hydrogen

Sulphide is an obnoxious (bad smelling) gas. It is produced mainly by the anaerobic (in absence of air) decomposition of organic matter. Other air polluting sulphur compounds are methyl mercaptan and dimethyle sulphide etc.

(v) Hydrogen fluoride: (v) Hydrogen fluoride: It is an

important pollutant even in very low concentrations. It is produced in the manufacturing of phosphate fertilizers.

(vi)(vi) ChlorineChlorine andand hydrogenhydrogen chloridechloride::It is mixed in the air either from theleakages from water treatment plants orother industries where it is produced orused. Hydrogen chloride is also evolved invarious industrial chemical processes. Themain effect of chlorine is respiratoryirritation which may be fatal.

(vii) Ozone: (vii) Ozone: It is a desirable gas in

the upper layers of atmosphere as it absorbs the UV radiation of sunlight. But near the earth surface it is a poisonous gas. It makes poisonous chemicals by photochemical reactions.

(viii) Aldehydes: (viii) Aldehydes: They are

produced by the incomplete oxidation of motor fuels and lubricating oil. They may also be formed because of photochemical reactions. Formaldehydes are irritating to the eyes.

Concentration of air pollutants

• It is common practice to express the quantities of gaseous pollutants present in air as parts per million (ppm), thus,

• Therefore,

0.0001 % by volume = 1ppm

Or

1 % by volume = 104 ppm

Mass of pollutant

• The mass of pollutants is expressed as micrograms/cu. M of air

• i.e.

General relation

Relation between ppmand micrograms/cu.m

(p)

Where, T= Temperature in Kelvin= 273 + temp in degree CelsiusMi = molecular weight of specie iR= universal gas constantp= pressure

] x 103] 1. at 250C and 1 atmpressure (760 mm of Hg)

2. At 0oC and 1 atmpressure (760 mm of Hg)

22.41

important data required for problems

• For calculation of Molecular wt we must know atomic wts of different elements

• O = 16

• H = 1

• C = 12

• S = 32

• N =14

Try this small but simple test

• Calculate molecular wt.s of

1. CO2

2. NO

3. SO2

Objective questions

1. The air transported pollen grains range mainly between ________and________ microns.

2. ______________ consists of finely divided particles produced by incomplete combustion.

3. __________refers to visible aerosols in which dispersed medium is liquid.

4. ________________ is oxidant gas formed by photochemical reaction.

5. _______________ are produced by the incomplete oxidation of motor fuels and lubricating oil.

6. 1 % by volume = _____ ppm

Theory questions

Q1. Define the following

1. Fumes

2. Smoke

3. Aerosol

4. Mist

5. Fog

Q2. Give relation between ppm and

gm/m3 at different conditions