Air pollution - Course

Air pollution

Air pollution is a chemical, physical (e.g. particulate matter), or biological agent that modifies the natural characteristics of the atmosphere. Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory diseases.

Pollutants

There are many substances in the air which may impair the health of plants and animals (including humans), or reduce visibility. These arise both from natural processes and human activity. Substances not naturally found in the air or at greater concentrations or in different locations from usual are referred to as 'pollutants'.

Pollutants can be classified as either primary or secondary:

Primary pollutants are substances directly produced by a process, such as ash from a volcanic eruption or the carbon monoxide gas from a motor vehicle exhaust.

Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react or interact.Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.

Sources of air pollutionAnthropogenic sources (human activity) related to burning different kinds of fuelCombustion-fired power plants Controlled burn practices used in agriculture and forestry management •Motor vehicles generating air pollution emissions. •Marine vessels, such as container ships or cruise ships, and related port air pollution. •Burning wood, fireplaces, stoves, furnaces and incinerators

Other anthropogenic sources•Oil refining, power plant operation and industrial activity in general. •Chemicals, dust and crop waste burning in farming. •Fumes from paint, hair spray, varnish, aerosol sprays and other solvents. •Waste deposition in landfills, which generate methane. •Military uses, such as nuclear weapons, toxic gases, germ warfare and rocketry.

Natural sources•Dust from natural sources, usually large areas of land with little or no vegetation. •Methane, emitted by the digestion of food by animals, for example cattle. •Radon gas from radioactive decay within the Earth's crust. •Smoke and carbon monoxide

from wildfires. •Volcanic activity, which produce sulfur, chlorine, and ash particulates.

Indoor air pollution, or Indoor air quality

The lack of ventilation indoors concentrates air pollution where people have greatest exposure times.Indoor pollution fatalities may be caused by using pesticides and other chemical sprays indoors without proper ventilation, and many homes have been destroyed by accidental pesticide explosionsCarbon monoxide (CO) poisoning is a quick and silent killer, often caused by faulty vents and chimneys, or by the burning of charcoal indoors.Indoors, the lack of air circulation allows these airborne pollutants to accumulate more than they would otherwise occur in nature.

Health effects

The World Health Organization thinks that 4.6 million people die each year from causes directly attributable to air pollution.

Many of these mortalities are attributable to indoor air pollution.

Worldwide more deaths per year are linked to air pollution than to automobile accidents.

Research published in 2005 suggests that 310,000 Europeans die from air pollution annually.

Reduction effortsThere are many air pollution control technologies and urban planning strategies available to reduce air pollution; however, worldwide costs of addressing the issue are high.Many countries have programs to or are debating how to reduce dependence on fossil fuels for energy production and shift toward renewable energy technologies or nuclear power plants.

Control devices

The following items are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.•Particulate control

Mechanical collectors (dust cyclones, multicyclones) Electrostatic precipitatorsFabric filters (baghouses) Particulate scrubbers

•NOx control Low NOx burners Selective catalytic reduction (SCR) Selective non-catalytic reduction (SNCR) NOx scrubbers Exhaust gas recirculationCatalytic converter (also for VOC control)

•VOC abatement Adsorption systems, such as activated carbon Flares Thermal oxidizersCatalytic oxidizersBiofiltersAbsorption (scrubbing)Cryogenic condensers

•Mercury control Sorbent Injection TechnologyElectro-Catalytic Oxidation(ECO) K-Fuel

Dioxin and furan control Ambient cleaning systemsAssociated equipment

•Source capturing systems•Continuous emissions monitoring systems (CEMS)

•Acid Gas/SO2 control

Wet scrubbersDry scrubbersFlue gas desulfurization