2008 Dec Holiday Assignment

Hello to all, this is our chosen assignment, topic no. 1; composition of air, fractional distillation of air & pollutants in the air.

The group members are Charlene Tan (15), Clement Loh (23), Paxton Lim (28), Brandon Ang (20) & Eugene Cheung (22).

Pollutants in the Air

POLLUTANTS

Major primary pollutants produced by human activity include:

• Sulfur Oxides(SO_x) especially sulfur dioxide a chemical compound with the formula SO₂. SO₂ is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain.[2] This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• Nitrogen oxides (NO_x) especially nitrogen dioxide are emitted from high temperature combustion. Can be seen as the brown haze dome above or plume downwind of cities.Nitrogen dioxide is the chemical compound with the formula NO₂. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO₂ is one of the most prominent air pollutants.
• Carbon monoxide is colourless, odourless, 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 greenhouse gas emitted from combustion.
• Volatile organic compounds VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of 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.

• Particulate matter Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulate matter can be man made or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.

• 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 include:

• Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog .Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. 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 sunlight 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.

Minor air pollutants include:

• A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive.
• A variety of persistent organic pollutants, which can attach to particulate matter.

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.

Composition of Air

Air Composition

"Aero" meaning air in latin is the name give to the mixture of gases which make up the Earth's atmosphere. The composition, physical, and chemical properties of air are very similar everywhere.

It is useful to think of the air which we encounter every day as being a locally-produced mixture of three types of "ingredients":

• Standard dry air, which is mainly composed of three gases: nitrogen (about 78%), oxygen (about 21%), and argon (about 1%). Together, these three gases make up 99.96% of dry air. All three can be economically recovered as industrial gas products. Standard dry air also contains a small amount of carbon dioxide, and very small amounts of neon, helium, krypton, hydrogen and xenon.

• Water vapor (humidity). The amount of water vapor in air at ground level can vary quite a bit - from almost zero to about 5 percent. Many factors influence the amount of humidity in the air at a given location and time.

• Other constituents (which are usually present in trace amounts) which reflect local condition.

At one glance, the pie chart could only show the rough percentage of the different gases in the atmosphere but it is certainly more convenient to remember the main points

	The sea-level composition of air (in percent by volume at the temperature of 15°C and the pressure of 101325 Pa) is given below in a chart.
	Nitrogen		N2	78.084 %
	Oxygen		O2	20.9476 %
	Argon		Ar	0.934 %
	Carbon Dioxide		CO2	0.0314 %
	Neon		Ne	0.001818 %
	Methane		CH4	0.0002 %
	Helium		He	0.000524 %
	Krypton		Kr	0.000114 %
	Hydrogen		H2	0.00005 %
	Xenon		Xe	0.0000087 %

Fractional Distillation of Air

Fractional Distillation of Liquid Air

Fractional distillation of liquid air (which is gotten by cooling air till it becomes a liquid at very low temperatures approx -194.35°C) is also used in air separation as by allowing the temperature of the liquid air to rise. Each gas will distill off at its own boiling point. , which through fractional distillation the air which has become liquid producing liquid oxygen, liquid nitrogen, and high purity argon. Distillation of chlorosilanes also enable the production of high-purity silicon for use as a semiconductor.