Air pollution :  Sources, effects and control measures

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere.

Sources

Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants into the atmosphere. These sources can be classified into two major categories which are:

Anthropogenic sources (human activity) mostly related to burning different kinds of fuel

·         "Stationary Sources" include smoke stacks of power plants, manufacturing facilities (factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating devices, chemicals, dust and controlled burn practices in agriculture and forestry management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the germination of some desirable forest trees, thus renewing the forest, fumes from paint, hair spray, varnish, aerosol sprays and other solvents. Waste deposition in landfills, which generate methane. Methane is not toxic; however, it is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement

·         "Mobile Sources" include motor vehicles, marine vessels, aircraft and the effect of sound, Military, such as nuclear weapons, toxic gases, germ warfare and rocketry etc.

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. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking

·         Smoke and carbon monoxide from wildfires

·         Vegetation, in some regions, emits environmentally significant amounts of VOCs on warmer days. These VOCs react with primary anthropogenic pollutants—specifically, NO_x, SO₂, and anthropogenic organic carbon compounds—to produce a seasonal haze of secondary pollutants.

·         Volcanic activity, which produce sulfur, chlorine, and ash particulates

primary pollutants (directly emitted from a process)

·         Sulfur oxides (SO_x) - SO₂ is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulphur compounds, their combustion generates sulfur dioxide.

·         Nitrogen oxides (NO_x) - Can be seen as the brown haze dome above or plume downwind of cities.

·         Carbon monoxide - is a colourless, odorless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.

·         Carbon dioxide (CO₂) - a colourless, odorless, non-toxic greenhouse gas associated with ocean acidification, emitted from sources such as combustion, cement production, and respiration

·         Volatile organic compounds – (VOCs) Methane (CH₄) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is another dangerous compound which is often associated with industrial uses. Methane from agricultural fields.

·         Particulate matter - Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.

·         Persistent free radicals connected to airborne fine particles could cause cardiopulmonary disease.

·         Sulphides toxic metals, such as lead, cadmium and copper.

·         Chlorofluorocarbons (CFCs) - harmful to the ozone layer emitted from products currently banned from use.

·         Ammonia (NH₃) - emitted from agricultural processes. Ammonia is a compound with the formula NH₃. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.

·         Odors — such as from garbage, sewage, and industrial processes

·         Radioactive pollutants - produced by nuclear explosions, war explosives, and natural processes such as the radioactive decay of radon.

Secondary pollutants (Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact) include:

·         Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.

·         Ground level ozone (O₃) formed from NO_x and VOCs. Ozone (O₃) is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant, and a constituent of smog.

·         Peroxyacetyl nitrate (PAN) - similarly formed from NO_x and VOCs.

·         Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment.

Effects of air pollution

1.   Global warming

Global warming is the temperature rise that is unequivocally underway in Earth's atmosphere and oceans. Scientists have determined that global warming is caused mostly by human activities that increase concentrations of greenhouse gases in the atmosphere, such as deforestation and burning of fossil fuels.

The instrumental temperature record shows that the average global surface temperature increased by 0.74 °C (1.33 °F) during the 20th century. Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global surface temperature is likely to rise a further 1.5 to 1.9 °C (2.7 to 3.4 °F) for their lowest emissions scenario and 3.4 to 6.1 °C (6.1 to 11 °F) for their highest.

An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, and a probable expansion of subtropical deserts. Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent occurrence of extreme weather events including heat waves, droughts and heavy rainfall events, species extinctions due to shifting temperature regimes, and changes in agricultural yields. Warming and related changes will vary from region to region around the globe, though the nature of these regional changes is uncertain. In a 4°C world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved.

2.       Acid rain

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen oxides which react with the water molecules in the atmosphere to produce acids. Governments have made efforts since the 1970s to reduce the release of sulfur dioxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. The chemicals in acid rain can cause paint to peel, corrosion of steel structures such as bridges, and erosion of stone statues.

3.         Climate change

Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions, or in the distribution of weather around the average conditions (i.e., more or fewer extreme weather events). Climate change is caused by factors that include oceanic processes (such as oceanic circulation), variations in solar radiation received by Earth,plate tectonics and volcanic eruptions, and human-induced alterations of the natural world; these latter effects are currently causing global warming, and "climate change" is often used to describe human-specific impacts.

Scientists actively work to understand past and future climate by using observations and theoretical models. Borehole temperature profiles, ice cores, floral and faunal records, glacial and periglacial processes, stable isotope and other sediment analyses, and sea level records serve to provide a climate record that spans the geologic past. More recent data are provided by the instrumental record. Physically-based general circulation models are often used in theoretical approaches to match past climate data, make future projections, and link causes and effects in climate change

4. Ozone acidification

Carbon dioxide (CO₂) - a colourless, odorless, non-toxic greenhouse gas associated with ocean acidification, emitted from sources such as combustion, cement production, and respiration

5.           Health effects

The World Health Organization states that 2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution. "Epidemiological studies suggest that more than 500,000 Americans die each year from cardiopulmonary disease linked to breathing fine particle air pollution. " A study by the University of Birmingham has shown a strong correlation between pneumonia related deaths and air pollution from motor vehicles. Worldwide more deaths per year are linked to air pollution than to automobile accidents. Published in 2005 suggests that 310,000 Europeans die from air pollution annually. Causes of deaths include aggravated asthma, emphysema, lung and heart diseases, and respiratory allergies. The US EPA estimates that a proposed set of changes in diesel engine technology (Tier 2) could result in 12,000 fewer premature mortalities, 15,000 fewer heart attacks, 6,000 fewer emergency room visits by children with asthma, and 8,900 fewer respiratory-related hospital admissions each year in the United States. Air pollution is also emerging as a risk factor for stroke, particularly in developing countries where pollutant levels are highest.

The worst short term civilian pollution crisis in India was the 1984 Bhopal Disaster. Leaked industrial vapours from the Union Carbide factory, belonging to Union Carbide, Inc., U.S.A., killed more than 25,000 people outright and injured anywhere from 150,000 to 600,000. The United Kingdom suffered its worst air pollution event when the December 4 Great Smog of 1952 formed over London. In six days more than 4,000 died, and 8,000 more died within the following months. An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have been the cause of hundreds of civilian deaths. The worst single incident of air pollution to occur in the United States of America occurred in Donora, Pennsylvania in late October, 1948, when 20 people died and over 7,000 were injured.

The health effects caused by air pollution may include difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions. These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body's respiratory system and the cardiovascular system.

Effect on biodiversity

          Acid rain affects the biodiversity

Control measures

1.   Mobile sources

§  Increasing fuel efficiency

§  hybrid vehicles

§  Alternate vehicles

§  Conversion to cleaner fuels

§  Use of sulphur free fuels

§  Use of bioethanol

§  Use of electric bikes

Industrial sources

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

·         Particulate control

o    Mechanical collectors (dust cyclones, multicyclones)

o    Electrostatic precipitators: Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.

o    Baghouses: A dust collector Designed to handle heavy dust loads distinguished from air cleaners which utilize disposable filters to remove the dust.

• Scrubbers
• Baffle spray scrubber
• Cyclonic spray scrubber
• Ejector venturi scrubber
• Mechanically aided scrubber
• Spray tower
• Wet scrubber

Wet scrubbers: Wet scrubber is a form of pollution control technology. The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants.

·         NOx control

o    Low NOx burners

o    Selective catalytic reduction (SCR)

o    Selective non-catalytic reduction (SNCR)

o    NOx scrubbers

o    Exhaust gas recirculation

o    Catalytic converter

·         VOC abatement

o    Adsorption systems, such as activated carbon

o    Flares

o    Thermal oxidizers

o    Catalytic converters

o    Biofilters

o    Absorption (scrubbing)

o    Cryogenic condensers

o    Vapor recovery systems

·         Acid Gas/SO₂ control

o    Wet scrubbers

o    Dry scrubbers

o    Flue gas desulfurization

·         Mercury control

o    Sorbent Injection Technology

o    Electro-Catalytic Oxidation (ECO)

o    K-Fuel

·         Dioxin and furan control

Plasma pyrolisis

Planned burning at more than 850⁰C

Avoiding open burning

·         Miscellaneous associated equipment

o    Source capturing systems

o    Continuous emissions monitoring systems (CEMS)

·         Avoid burning of agricultural residues instead go for in situ composting