Definition The presence of any solid,

liquid, or gaseous substance (including noise) present in the atmosphere in such concentrations that may or tend to be injurious to human beings, or other living creatures, or plants, or property, or enjoyment.

Hippocrates King Edward 1 – London smog - 1952 Europe – black peppered moths Bhopal tragedy -1984- MIC

Major Causes High rate of population growth Urbanization Rapid industrialization TransportationSources Natural Sources Man Made Sources

Clean dry air contains by volumeNitrogen ~ 78.1%Oxygen ~ 20.9%Other gases including CO2, Helium, Argon,

Neon, Krypton, Nitrous Oxide etc ~ 1%

Personal – exposure of an individual to dust, fumes, and gases

Occupational – exposure of an individual to aerosols, vapours, and gases in harmful concentrations in their working or occupational environment

Community – pollution from a variety of sources and factors which cause adverse social, economic, and health effects on man’s total environment

Pollutants includeOxides of nitrogen from electrical stormsHydrogen flouride and hydrogen chloride

from volcanic disturbancesSulphur dioxide, hydrogen sulphide etc

from volcanoes or from the action of sulphide bacteria

Ozone formed photo chemically or from electrical discharges

Carbon monoxide from atmospheric oxidation of methane and formaldehyde

Dust, aerosols, and suspended particulate matter (SPM) from natural sources consisting of salt particles from sea water airborne particles from soil and vegetation dust of meteoric origin bacterial spores, and pollen dust, ash, and gases from volcanic action dust from dust storms smoke of forest fires mineral particles from erosion of rocks

SPM consists of all atmospheric particles,

either solid or liquid, dispersed in a gaseous medium

Aerosolsrefer to the dispersion of solid or liquid

particles of microscopic size in a gaseous medium such as smoke, fog, mist etc (generally solid and liquid particles in the size range 100 microns down to 0.01 microns or less)

Dust – solid particles larger than colloidal particles that are capable of temporary suspension in air or other gases (size range ~ 1 to 200 microns)

Smoke – finely divided particles resulting from incomplete combustion or other chemical processes – predominantly carbon particles (~<1micron)

Mist – Liquid droplets formed by condensation or released from industrial operations

Fog Fumes

Radioactive natural sources consist of radioactive minerals in the earth’s crust (derived from the uranium series, thorium series, and the actinium series)

Those generated by the action of cosmic rays from the outer space on the gaseous constituents of the atmosphere (radon and thoron)

Atmospheric Reactions Natural chemical reactions taking place in the

lower atmosphere convert gases or vapours into solids and liquid products by oxidation, condenstion, and polymerisation mechanisms

In the upper atmosphere, photochemical reactions may break down complex molecules by absorption of high energy UV solar radiation and resultant oxidation and other reactions

Carbon dioxide gas is released by all forms of life during respiration

Products of combustion of fuel in houses Exhaust gases from automobiles Industrial activities – eg. Metal smelting,

refining, iron and steel manufacture, oil refining, chemical and petrochemical operations, manufacture of pulp and paper

An estimate of dust fall in the most contaminated areas - ~ 50 to 100tons/sq.km/ month

Sulphur DioxideThermal Power stations are the main

source - ~ 40% of the total emissionAnnual contribution from combustion of

coal and petroleum products - >20 M tons/yr

Nitrogen OxidesCombustion of fuelsMajor contributor- automobilesOthers include thermal power stations,

industries, households etc

Carbon Monoxide Exhaust of automobiles and coal burning Incomplete combustion of carbanaceous fuels ~ 500 M tons/yr

Hydrocarbons from automobile exhausts, smoke of incinerators,

from oil refineries etc Photochemical Oxidants Aldehydes

from the combustion of fuel

Primary pollutants Secondary pollutants

Emitted directly from identifiable sourcesPollutants from natural or anthropogenic

sources in the atmosphere Includes particulate matter, suplhur oxides and

sulphur compounds, nitrogen oxides, CO, compounds of halogens, radioactive compounds, photochemical oxidants, hydrocarbons etc

Formed as a result of the interaction between two or more primary pollutants or by reactions with normal atmospheric constituents – generally chemicals – very harmful

Sulphuric acid, ozone, photochemical smog, peroxy acetyl nitrate (PAN)

H2SO4 –SO2 and H20 vapour

O3 -HC and NO

Stationary Sources industrial installations

Mobile Sources automobiles

Point sources (large stationary sources)

Line sources (mobile sources with definite route)

Area sources (small stationary sources like residential buildings and mobile sources with indefinite route)

Combustion of gasoline and other hydrocarbon fuels in cars, trucks, and airplanes

Burning of fossil fuels (oil, coal, and dinosaur bones)

Insecticides Herbicides Everyday radioactive fallouts Dust from fertilizers Mining operations Livestock feedlots

Synchronym of smoke and fog Types

Photochemical Air stagnation, abundant sunlight, high concentrations

of hydrocarbons and nitrogen oxides in the atmosphere

Occurs in metros First observed in LA in the 1940s Caused by the interaction of some hydrocarbons and

oxidants under the influence of sunlight giving rise to the dangerous Peroxy acyl nitrate (PAN)

Coal induced From burning coal – smoke, flyash, suplhur compounds Occurs in cold climate when calm meteorological

conditions prevail

particulates (especially lead)

hydrocarbons nitrous oxides potassium carbon monoxide peroxy acetyl nitrate

(PAN) other toxic chemicals

Photochemical SmogCoughing and soar throat Irritation of eyesKills leaf tissuesReduces visibilityDegrades rubber, cellulose etc

Coal-induced Smog

Prolonged exposure may cause high mortality rate among elderly people and those having heart and lung diseases like chronic bronchitis, asthma, broncho-pneumonia etc

Smog in London on 8th December, 1952 – more than 4000 people died due to suffocation

Efficient insulation Bacteria Molds and mildews Viruses animal dander and cat saliva plants house dust Mites Cockroaches pollen

Acid rain Ozone layer depletion Global warming In human population respiratory

problems, allergies, and a risk for cancer

contains high levels of sulfuric or nitric acids

contaminates drinking water and vegetation

damages aquatic life erodes buildings Alters the chemical

equilibrium of some soils

Status of Particulate Emission

Effect on VegetationSO2 severely damages sensitive

vegetation

Effect on Human Health In moderate climates and low altitudes,

excess mortality has been noted among people with pulmonary and cardiac problems when SO2 and SPM concentrations are high

Also affects visibility in warmer climates

CO combines with haemoglobin of blood, when inhaled, and impairs transfer of oxygen to tissues - ~20% carboxyhaemoglobin may cause headache and lassitude and impair performance – high levels also affect the cardiovascular system

NO2 – respiratory system diseases

Photochemical oxidants – asthma, irritation of eyes, nose, and throat

Effects on Physical Properties of the Atmosphere

First indication – Decrease in VisibilityAlso, observations of visibility in polluted areas show strong directional variations – due to scattering and absorption of light by particles suspended in air, visibility is lower in the direction of the sun

Other meteorological factors such as inversion, wind speed and height also affect visibilityVisibility depends on transmission of light through the atmosphere ability of the eye to distinguish an object (based on

contrast)Reduced visibility is related to Size Concentration physical characteristics of the particulate matter in air

Affects solar radiation in urban areas, thereby affecting the urban atmosphere and weather Solar radiation may be reduced by ~ 30% City may be 5-10% more cloudy, 100% more

foggy in winter Fog remains for much longer duration Frequency of occurrence of fog increase

Affects atmospheric constituents Steady increase in atmospheric CO2 Increase in lead concentration

Effects on MaterialsMechanisms by which pollutants

deteriorate materials includeAbrasionDeposition and removalDirect chemical attack Indirect chemical attackCorrosion