Untitled Essay Research Paper Gifted Chemistry IBAlternative

Untitled Essay, Research Paper

Gifted Chemistry IB

Alternative Assessment

Photochemical SmogHistorically, the term smog referred to a mixture of smoke and fog, hence the name smog.

The industrial revolution has been the central cause for the increase in pollutants in the

atmosphere over the last three centuries. Before 1950, the majority of this pollution was

created from the burning of coal for energy generation, space heating, cooking, and

transportation. Under the right conditions, the smoke and sulfur dioxide produced from the

burning of coal can combine with fog to create industrial smog. In high concentrations,

industrial smog can be extremely toxic to humans and other living organisms. London is

world famous for its episodes of industrial smog. The most famous London smog event

occurred in December, 1952 when five days of calm foggy weather created a toxic atmosphere

that claimed about 4000 human lives. Today, the use of other fossil fuels, nuclear power,

and hydroelectricity instead of coal has greatly reduced the occurrence of industrial

smog. However, the burning of fossil fuels like gasoline can create another atmospheric

pollution problem known as photochemical smog. Photochemical smog is a condition that

develops when primary pollutants (oxides of nitrogen and volatile organic compounds

created from fossil fuel combustion) interact under the influence of sunlight to produce a

mixture of hundreds of different and hazardous chemicals known as secondary pollutants.

Development of photochemical smog is typically associated with specific climatic

conditions and centers of high population density. Cities like Los Angeles, New York,

Sydney, and Vancouver frequently suffer episodes of photochemical smog.One way in which the production of photochemical smog is initiated is through the

photochemical reaction of nitrogen dioxide (NO2) to form ozone. There are many sources of

photochemical smog, including vehicle engines (the number one cause of photochemical

smog), industrial emissions, and area sources (the loss of vapors from small areas such as

a local service station, surface coatings and thinners, and natural gas leakage).Vehicle engines, which are extremely numerous in all parts of the world, do not completely

burn the petroleum they use as fuel. This produces nitrogen dioxide which is released

through the vehicle exhaust along with a high concentration of hydrocarbons. The

absorption of solar radiation by the nitrogen dioxide results in the formation of ozone

(O3). Ozone reacts with many different hydrocarbons to produce a brownish-yellow gaseous

cloud which may contain numerous chemical compounds, the combination of which, we call

photochemical smog.Both types of smog can greatly reduce visibility. Even more importantly, they pose a

serious threat to our health. They form as a result of extremely high concentrations of

pollutants that are trapped near the surface by a temperature inversion. Many of the

components which make up these smogs are not only respiratory irritants, but are also

known carcinogens.There are many conditions for the development of photochemical smog:1. A source of nitrogen oxides and volatile organic compounds.2. The time of day is a very important factor in the amount of photochemical smog present.• Early morning traffic increases the emissions of both nitrogen oxides (NOx) and

Peroxyacetyl Nitrates (PAN) as people drive to work.

• Later in the morning, traffic dies down and the nitrogen oxides and volatile

organic compounds begin to react forming nitrogen dioxide, increasing its concentration.

• As the sunlight becomes more intense later in the day, nitrogen dioxide is broken

down and its by-products form increasing concentrations of ozone.

• At the same time, some of the nitrogen dioxide can react with the volatile organic

compounds (VOCs) to produce toxic chemicals.

• As the sun goes down, the production of ozone is halted. The ozone that remains in

the atmosphere is then consumed by several different reactions.3. Several meteorological factors can influence the information of photochemical smog.

These conditions include :• Precipitation can alleviate photochemical smog as the pollutants are washed out of

the atmosphere with the rainfall.

• Winds can blow photochemical smog away replacing it with fresh air. However,

problems may arise in distant areas that receive the pollution.

• Temperature inversions can enhance the severity of a photochemical smog episode.

Normally, during the day the air near the surface is heated and as it warms it rises,

carrying the pollutants with it to higher elevations. However, if a temperature inversion

develops pollutants can be trapped near the Earth’s surface. Temperature inversions cause

the reduction of atmospheric mixing and therefore reduce the vertical dispersion of

pollutants. Inversions can last from a few days to several weeks.4. Topography is another important factor influencing how sever

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