Air Pollution: causes and control

PRESENTED BY:VISHNURAJ R.S

DEPT.AQUATIC BIOLOGY &FISHERIES

Air is one of the vital part of life .Air supplies with oxygen is essential for our bodies to live. Air is 99.9% nitrogen, oxygen, water vapors and inert gases. Due to man made activities along with some natural processes many physical addition of material that turn the air impure or unclean. That is called air pollution.

Air Pollution

Air PollutionAir pollution primarily comes from burning fossil fuels such as natural gas, petroleum, and coal. Humans are the main cause of air pollution. Industry, including factories and power plants, burn large quantities of fuel. Burning coal and petroleum releases sulfur oxides and nitrogen oxide into the air. Airplanes, boats, and cars burn petroleum, releasing carbon monoxide and carbon dioxide.

Air Pollution

Some air pollution is not directly caused by humans: for example, animals emit carbon dioxide when they breathe, and volcanoes release sulfur oxide. The forest fire produce huge amount of CO,CO2, Nitrogen oxides, semi burnt hydro carbons, and ash.The waste in landfills releases methane. Sulfur oxides, carbon monoxide and carbon dioxide, and methane all have a very negative effect on air quality. These pollutants can also contribute to the greenhouse effect. The dust storm make the air full of particulate sand particles.

Primary vs Secondary pollutants

• Not all of the pollutants found in the atmosphere are the direct result of emissions.

• Many pollutants arise from chemical reactions in the atmosphere with other substances or light (photochemical reactions).

•Pollutant substances that are directly emitted into the atmosphere = primary pollutants. •Substances not directly emitted into the atmosphere, formed by chemical reactions in the atmosphere = secondary pollutants.

TYPES OF POLLUTION INDOOR POLLUTION• Indoor air pollution occurs inside our homes, office and schools. • The main types of indoor pollutants are tobacco smoke, gases from

stoves and furnaces, household chemicals, small fiber particles, and hazardous fumes given off by building materials like insulation , glue, and paint .

• In high amounts it causes headache, eye irritation, etc.OUTDOOR POLLUTION• Gases and particulates form of pollutants pour into the atmosphere

from the burning of fuel to motor vehicles, heat buildings, business and industrial processes , burning of garbage etc…

• Outdoor pollution make huge impacts on atmosphere and the organisms

• Acid rain , global warming, etc are some of its consequences .

TYPES OF POLLUTANTS Aerosols

– Particulates solid phase• Dust• Ash• Fumes

– Solid and liquid• Smoke (from combustion)• Coastal aerosols

– Liquid – Aggregate gases (sulfate, nitrate)

GasesCOxSOxNOxPAH

Six primary or “criteria” air pollutants

• Carbon monoxide (CO)• Sulfur oxides (SOx)

• Nitrogen dioxide (NO2)

• Ozone (O3)• Hydrocarbons• Particulate matter(PM2.5 _PM10)

Carbon Monoxide

•colorless, odorless, tasteless, non irritating gas

•produced when carbon does not burn in fossil fuels,ie incomplete combustion.

•Commonly present in automobile exhaust

•deprives body of O2 causing headaches, fatigue, and impaired vision, it may lethal when continually inhale concentration above 1000ppm over a period of 4 hours.

Sulfur Dioxide

•Colourless gas with penetrating and pungent odour

•produced mainly when coal and fuel oil are burned

•present in power plant exhaust

•narrows the airway, causing wheezing and shortness of breath, especially in those with asthmaThe formation of SO2, SO3, and sulfuric acid

S + O2 SO2

2 SO2 + O2 2SO3

SO3 + H2O H2SO4

Nitrogen Dioxide

•reddish, brown gas

•produced when nitric oxide combines with oxygen in the atmosphere

•present in car exhaust and power plants

•affects lungs and causes wheezing; increases chance of respiratory failure.

•Smokers may readily develop lung disease as cigarettes and cigars containing 330 to 1,500 ppm nitrogen oxides. Prolonged exposure at 1 to3 ppm or even less may fatal. •It also react with water to cause acid rain 4NO2+2H2O+O2 ------- 4HNO3

Ground Level Ozone

•It is a highly reactive pale-blue gas with penetrating odour.

• at upper level, ozone shields Earth from sun’s harmful UV rays

•at ground level, ozone is harmful pollutants

•formed from automobile, power and chemical plant exhaust

•irritate respiratory system and asthma; reduces lung function by inflaming and damaging lining of lungs

•It also a green house gas

HYDROCARBONS•Hydrocarbons are compounds that have carbon and hydrogen•Benzene, benzpyrene, methane, etc are common hydrocarbon pollutants.•The major sources are automobile and industrial exhaust..•Benzene: colorless, flammable liquid pollutant have carcinogenic property…•Benzpyrene: it is also carcinogenic,•Methane is common green house gas .. It produce by naturally along with human activities.

Particulate Matter

•particles of different sizes and structures that are released into the atmosphere…

•Lead, asbestos etc are some particulate matter from man made sources…

•present in many sources including fossil fuels, dust, smoke, fog, forest fire etc.

•Along with these industrial operations like mining, polishing etc also produce..

•can build up in respiratory system

•aggravates heart and lung disease; increases risk of respiratory infection

Methods of air pollution control can be divided into two categories: •THE CONTROL OF PARTICULATE EMISSIONS •THE CONTROL OF GASEOUS EMISSIONSThe term particulate refers to tiny particles of matter such as smoke, soot, and dust that are released during industrial, agricultural, or other activities.Gaseous emissions are industrial products such as sulfur dioxide, carbon monoxide, and oxides of nitrogen also released during various manufacturing operations.

Control of Air Pollutants

1. Particulates – Cyclones separation by centrifugation –

Cyclone utilise centrifugal force generated by a spinning gas stream to separate the particulate matter from the carrier gas.The general principle of inertia separation is that the particulate-laden gas is forced to change direction. As gas changes direction, the inertia of the particles causes them to continue in the original direction and be separated from the gas stream.

THE CONTROL OF PARTICULATE EMISSIONS

dirty gas inlet

cleaned gas outlet

particulate outlet

Cyclone separator

2.Gravitational Settling Chamber

• Like settling basins in water and waste water treatment, settling chambers provide enlarged areas to minimize horizontal velocities of air flow thus allow time for gravity to carry the particle to the floor.

• These are simple in design and operation but they require large spaces for installation and have relatively low efficiency especially for removal of small particles.

•

3.Particulates – FiltrationFibre bags commonly used for control of

particulate emissions with very high dust loadings and smaller particles.

• Filters consist of porous structure composed of granular or fibrous material which tends to retain the particulate matter as the carrier gas passes through the voids of the filter.

• The dust is collected on the inside of the bag surface and the filtered gas is discharged to the atmosphere -

99% efficient

4.Particulates – Wet Scrubbers• spray systems where fine water droplets are sprayed

at high velocity at right angles to the emerging gas • Most of the particles in the gas stream are scavenged

by the water droplets, which fall and are collected along with the particles

• relatively low efficiencies (80-90%) and is usually employed as a pre-cleaner to remove particles larger than 5m

• pass dirty gas through a series of fine wires (coronas) charged with DC current – causes particles to aggregate & precipitate

• Alternatively corona produces negative ions that cause particles in the gas stream to become negatively charged, and attracted to positive terminal – where they aggregate and fall into a collection hopper

• Large precipitators and low gas flow rates give better results

5.Particulates – Electrostatic Precipitators

charged electrodes soot laden smoke inlet

soot free gas escape

removal of soot particles earth point

Gaseous pollutants –Process Modifications

• simplest and least expensive methods for the control of gaseous pollutants

• fuel substitution e.g. low sulfur coal, or fuel oils in place of cheaper coal can greatly reduce the amount of SO2 emissions at the source

• This type of source control is always the best approach wherever possible

Gaseous pollutants - Combustion• involves a series of complex chemical reactions in which

oxygen is combined with organic molecules, to form CO2 and H2O

• commonly referred to as incineration or afterburning

Gaseous pollutants - Adsorption• physical adsorption to solid surfaces • Reversible - adsorbate removed from the adsorbent by

increasing temp. or lowering pressure • widely used for solvent recovery in dry cleaning, metal

degreasing operations, surface coating, and rayon, plastic, and rubber processing

• limited use in solving ambient air pollution problems – with its main use involved in the reduction of odour

• Adsorbents with large surface area to volume ratio (activated carbon) preferred agents for gaseous pollutant control

• Efficiencies to 99%

Gaseous pollutants - Absorption• Scrubbers remove gases

by chemical absorption in a medium that may be a liquid or a liquid-solid slurry

• water is the most commonly used scrubbing medium

• Additives commonly employed to increase chemical reactivity and absorption capacity

Gas pollutants – Vehicle emissions• generally involve simple procedures such as maintaining the

correct tuning for the engine, or the use of catalytic converters • catalytic converters use Pt and Pd attached to some form of

ceramic material • extremely high surface area (in hundreds of m2) allows catalytic

materials to contact exhaust gases, oxidising them to CO2 and water vapour

BIOFILTERS• When applied to air filtration and purification, biofilters use

microorganisms to remove air pollution.[1] The air flows through a packed bed and the pollutant transfers into a thin biofilm on the surface of the packing material. Microorganisms, includingbacteria and fungi are immobilized in the biofilm and degrade the pollutant. Trickling filters and bioscrubbers rely on a biofilm and the bacterial action in their recirculating waters.

• The technology finds greatest application in treating malodorous compounds and water-soluble volatile organic compounds(VOCs). Industries employing the technology include food and animal products, off-gas from wastewater treatment facilities,pharmaceuticals

Bioscrubbers

• bioscrubbers, the compound to be degraded first is absorbed in the liquid phase located in an absorption tower filled with liquid. The operation involves making the gas flow in a countercurrent through the liquid where the contaminants and oxygen are absorbed. Subsequently, the liquid is fed to a reactor packed with an inert material covered with biofilm that is responsible for degrading the pollutant. Bioscrubbers are the most suitable systems for the treatment of highly water-soluble compounds

CONCLUSION• Air pollution is a major global threat.• Natural and human activities causes pollution.• SOURCES!!!!• How it affects???• CONTROL MEASURES!!!