Essay On Photochemical Smog and Ozone Depletion

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Photochemical Smog and Ozone Depletion

The central cause of the increased pollutants in the atmosphere over the last three years has been said to industrial revolution .Before industrialization, majority of the pollutants were being caused by charcoal burning, space heating, and cooking end transportation. Smoke and sulphur produced from the burning of coal can combine with fog to form industrial smog. Industrial smog can be very toxic to humans and other living organisms if it is in high concentration. However, the burning of fossils fuels like gasoline can create another atmospheric hazard known as photochemical smog (Wings, n.d.).

This is a condition that develops when primary pollutants like oxides of nitrogen and volatile organic compounds generated from fossil fuel combustion, interact under the presence of sunlight to produce a mixture of many different hazardous chemicals known as secondary pollutants. On the other hand ozone layer depletion ozone depletion refers to the slow decline in the amount of ozone in the earth’s stratosphere since the late 1970’s.Ozone layer protects the earth from ultra violet rays sent down by sun, therefore if the ozone if depleted the effects on the planet could be catastrophic. To appreciate these effects of both ozone layer depletion and photochemical smog, it is important to explore both tenets in depth beginning with photochemical smog (Oblack, 2009).

2.0 Photochemical smog

The following are some of the toxic chemicals that cause photochemical smog, their sources and their environmental effects.

2.1.1 Nitrogen oxides (NO and NO2) Sources

oCombustion of coal, gas in both automobiles and industry
oBacterial action in the soil
oForest fires
oVolcanic action
oLightening (Smith, 2010). Environmental effects

oDecreased visibility due to yellowish color of NO2
oNO2 contributes to heart and lung problems
oNO2 can suppress growth
oDecreased resistance to infection
oMay encourage the spread of cancer (Tucker, 2005).

2.1.2Volatile organic compounds

Evaporation of solvents
Evaporation of fuels
Incomplete combustion of fossil fuels
Naturally occurring compounds like terpenes from tees (EPA, n.d.). Environmental effects

oEye irritation
oRespiration irritation
oSome are carcinogenic
oDecreased visibility due to blue brown haze (EPA, n.d.).

2. 1.3.Ozone (O3) Sources

oFormed from the photolysis of NO2
oSome result from the stratospheric ozone intrusions (Nardo & Hall, 2005). Environmental effects

o It causes Bronchial constriction
oMay cause coughing and wheezing
oLeads to respiratory and eye irritation
oCauses decreased crop yields which may result from retarded growth of the crops
oDamages plastics
oBreaks down rubber
oThe gas has e harsh odor (Nardo & Hall, 2005).

2.1.4. Peroxyacetyl nitrates (PAN)

It is formed by reaction of NO2 with volatile organic compounds (Harrison, 2001).
2. 1.4.1 Environmental effects
oIt causes eye and respiratory irritation
oHigh toxity to plants
oAlso causes damage to proteins (Harrison, 2001).

2.2 Development of photochemical smog

The following are some of the conditions favorable for the formation of photochemical smog
a) Time of the day; in the morning and in evening traffic increases emissions of both nitrogen oxides and volatile organic compounds as people are driving to and from work respectively.
b) Some metrological factors can influence the formation or photochemical smog .they includes the following:

Precipitation can lead to photochemical smog as the pollutants are washed out of the atmosphere with the rain water
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 (Wang & Kwok, 2003).

c) Topography

Communities situated in valleys are more prone to photochemical smog because hills and mountains surrounding them tend to reduce the air flow, thus allowing high pollutants concentration. Moreover valleys are sensitive to photochemical smog since temperature inversions frequently develop in these areas (Wang & Kwok, 2003).

2.3 Chemistry of photochemical smog

To begin with, as explained earlier, the following conditions must be there for the formation of photochemical smog:
Presence of sunlight
Production of oxides of nitrogen
Production of volatile organic compounds
Temperatures greater than 180C (American Chemical Society, 2002).
If the criteria above are met therefore several reactions will occur producing toxic chemical constituents of photochemical smog. The following are some of the processes required in the formation of the two major toxic components: i.e. ozone and peroxyacetyl nitrate.
NO2 can be formed in either of the two processes as illustrated below;
O3+NO NO2 +O2
NO+RO2 NO2 + other products. Symbol R represents Hydrocarbons.
Sunlight cans breakdown nitrogen dioxide into nitrogen oxide.
The atomic oxygen formed in the above reaction then reacts with one of the abundant oxygen molecule (O2) to form ozone (O3) (American Chemical Society, 2002).
O+O2 O3
NO2 can also react with radicals produced from volatile organic compounds in a series of reactions to form toxic products like peroxyacetyl nitrates.(PAN)
NO2 + R- products such as PAN (American Chemical Society, 2002).

2.4 Areas affected by Photochemical Smog

Smog can form in almost any climate where industries or cities release large amounts of air pollution, such as smoke or gases. However, it is worse during periods of warmer, sunnier weather when the upper air is warm enough to inhibit vertical circulation. It is especially prevalent in geologic basins encircled by hills or mountains. It often stays for an extended period of time over densely populated cities or urban areas, such as London, Atlanta, Houston, Phoenix, Las Vegas, New Delhi, New York, Cairo, Los Angeles, Sacramento, São Paulo, Mexico City, Santiago of Chile, Toronto, Milan, Athens, Beijing, Shanghai, Manila, Hong Kong, Seoul, the Randstad or Ruhr Area and can build up to dangerous levels (Jacobs & Kelly, n.d.).

Victorian London was notorious for its thick smogs, a fact that is often recreated to add an air of mystery to a period drama. Severe episodes of smog continued in the 19th and 20th centuries and were nicknamed pea-soupers. The Great Smog of 1952 darkened the streets of London and killed approximately 4,000 people in the short time of 4 days while other 8,000 died from its effects in the following weeks and months. In 1956 the Clean Air Act introduced smokeless zones in the capital. Consequently, reduced sulfur dioxide levels made the intense and persistent London smog a thing of the past. It was after this the great clean-up of London began and buildings recovered their original stone facades which, during two centuries, had gradually blackened. Smog caused by traffic pollution, however, does occur in modern London (Russell., 2006).

The city of Mexico is also affected by the smog since it is located in the highland bowl, this means that cold air sinks onto the urban areas of the city trapping gases produced by industries and the motor vehicles. The Mexico City has changed within a generation from being one of the cleanest cities in Latin America to being smog plagued. Another episode of photochemical smog happened in December 2005 in the city of Tehran Iran, where 1600 people were taken to hospital, due to severe smog which was caused by unfiltered car exhaust (Jacobs & Kelly, n.d.).

In 1993, the attention of photochemical smog was brought into the attention of general United States public, since it was realized the effect of photochemical smog on human life and even the destruction of farmers 3000 acres of spinach crop. The United States Environmental Agency designated more than 300 United States counties to be non attainment areas for more than one pollutants tracked as part of the national ambient air quality standards. Los Angeles and the San Joaqui valley, are notorious for photochemical smog since they are based in the low basins surrounded by mountains. The major contributors of the smog (pollution) are the motor vehicles in the basins as well as the effects of the San Francisco Bay and Long Beach port complexes (Russell., 2006).

In Southern Asia smog is a regular problem and is mainly caused by land and forest fires in Indonesia, in particular Sumatra and Kalimantan. In most cases farmers and plantation owners are usually blamed for the fires which they use to clear tracts of land in expansion of their plantings. The fires mainly affect ;Brunei, Indonesia, Philippines, Malaysia, Singapore and Thailand, and occasionally Guam and Saipan. According to 1997 records the loses from the fires were estimated to 9 billion US dollars which included the damages in agriculture production, destruction of forests, health, transportation, tourism among many other economic endeavors (Russell., 2006).

2.5 Solutions to photochemical smog

Since automobile use, in particular the large volume of commuter traffic is one other primary factor in heightening the effects of photochemical smog. The solution would be to reduce commuter traffic and increase public transportation. Vehicle motors are the major contributors to the abundance of hydrocarbons and oxides of nitrogen in the atmosphere .Therefore use of other alternative modes of transportation like underground subway systems, city bus lines, and bicycles among many others can reduce thousands to millions of cars from entering to large cities (Miller & Spoolman, 2008).
If it is necessary to have a personal vehicle, then it would be advisable to multi task rather than returning to the city throughout the week to carry out individual errands. The motorist should opt for smaller, more fuel efficient compact cars, and to drive below the speed limit. Moreover the vehicles should be maintained regularly to prevent the emission of hydrocarbons. Other methods of reducing the occurrence of photochemical smog include:

Use of lawn equipment and tools that do not require gasoline will also reduce the hydrocarbons.
Use of latex water based paints rather than oil based paints which contain more toxic solvents than water based paints do.
Use clothes bags when shopping rather than using store plastic bags (Miller & Spoolman, 2008).

3.0 Ozone depletion

Ozone can be depleted by a number of free radical catalysts but the important ones are: hydroxyl radical(OH),the nitric oxide radical(NO),the atomic chlorine ion(CL-),and the atomic bromine ion(Br-).All these radicals have a natural and manmade sources, currently most of the OH- and NO in the stratosphere is of natural origin, but human activity has dramatically increased the levels of chlorine and bromine. These elements are found in stable organic compounds especially chlorofluoralcarborns (CFCs), which may find their way to the stratosphere without being destroyed in the troposphere due to their low reactivity. Once in the stratosphere Cl and Br atoms are liberated from the parent compounds by the action of ultraviolent light .for instance. (‘h” is Planck’s constant; ‘v’ is frequency of electromagnetic radiation) (Sinha, 1998).

CFCl3 + hν → CFCl2 + Cl
The Cl and Br atoms eventually have the possibility of destroying ozone molecules via an assortment of catalytic cycles. A perfect example of such a cycle is a chlorine atom which reacts with an ozone molecule then blends with an oxygen atom with it forming ClO) and ultimately leaving a normal oxygen molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of ozone (i.e., O3) to yield another chlorine atom and two molecules of oxygen. The chemical equation for the above named gas-phase reactions is as follows:

Cl + O3 → ClO + O2
ClO + O3 → Cl + 2 O2
Following the above, there is generally a decrease in the amount of ozone. More complicated mechanisms have been discovered that lead to ozone destruction in the lower stratosphere as well. Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances are mainly responsible for manmade chemical ozone depletion. The total amount of effective halogens (chlorine and Bromine) in the stratosphere can be calculated and are known as the Equivalent Effective Stratospheric Chlorine (UNEP, 1998).

3.1 Why ozone layer depletion is of great interest.

While the effect of Antarctic hole is decreasing, the global ozone is relatively low, estimated at about 4% per decade. The hole has generated interest because:
oThe decrease in the ozone layer was predicted in the early 1980s to be roughly 7% over a 60 year period (Harrison, 2001).
oThe sudden recognition in 1985 that there was a substantial "hole" was widely reported in the press. The especially rapid ozone depletion in Antarctica had previously been dismissed as a measurement error (Harrison, 2001).

oMany were worried that ozone holes might start to appear over other areas of the globe but to date the only other large-scale depletion is a smaller ozone "dimple" observed during the Arctic spring over the North Pole. Ozone at middle latitudes has declined, but by a much smaller extent (about 4–5% decrease) (Nardo & Hall, 2005).

oIf the conditions became more severe (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine), then global ozone may decrease at a much greater pace. Standard global warming theory predicts that the stratosphere will cool. When the Antarctic ozone hole breaks up, the ozone-depleted air drifts out into nearby areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the break-up of the Antarctic ozone hole (Wings, n.d.).

3.2Effects of ozone layer depletion

oEvery time 1% of the ozone layer is depleted, 2% more UV-B is able to reach the surface of the planet.  UV-B increase is one of the most harmful consequences of ozone depletion because it can cause skin cancer.
oThe increased cancer levels caused by exposure to this ultraviolet light could be enormous.  The EPA estimates that 60 million Americans born by the year 2075 will get skin cancer because of ozone depletion.  About one million of these people will die (NHMRC, 1989).
oIn addition to cancer, some research shows that a decreased ozone layer will increase rates of malaria and other infectious diseases.  According to the EPA, 17 million more cases of cataracts can also be expected (UNEP , 1998) (Smith, 2010). The environment will also be negatively affected by ozone depletion.  Consequently, plant life cycles will be altered disrupting the global food chain.  The effects on the animal life are bound to be adverse.
oOceans and other water bodies will be also hit hard.  For basic microscopic organisms for example plankton the effects may adverse and many may not be able to survive.  If that happened, it would mean that all of the other animals that are above plankton in the food chain would also die out.  Other ecosystems such as forests and deserts will also be harmed (Jones & Wigley, 1989).
oThe planet's climate could also be affected by depletion of the ozone layer.  Wind patterns could change, resulting in climatic changes throughout the world (Hoffmann, 2007).

3.3 Solutions to ozone layer depletion

The discovery of the ozone depletion problem came as a great surprise, now; actions must be taken to ensure the ozone layer is not destroyed .Because CFCs are so wide spread and used in such a wide variety of products, limiting their use is hard. Also since many products already contain components that use CFCs, it would be difficult if not possible to eliminate those CFCs already in existence. The problem of CFC may be hard to solve there are already great quantities of CFCs in the environment. CFCs would remain in the stratosphere for another 100 years even if none were ever produced again (Tyler, 2002).

Despite all these difficulties, international actions have been taken to limit CFCs. In the Montreal protocol, thirty nations worldwide agreed to reduce usage of CFCs and encouraged other countries to do so. However many environmentalists felt the treaty took the actions when it was already late. The treaty requested for CFC makers to only eliminate half of their CFC production, making some people fell that it was inadequate. By the year 2000, the United States and twelve other nations in Europe had agreed to ban all use and production of CFCs. This will be significant because these countries produce three quarters of the CFCs in the world. Many other countries have signed treaties and written laws restricting the use of CFCs, Companies are finding substitutes for CFCs, and people in general are becoming more aware of the dangers of ozone depletion (Shaila, Payal, & Victoria, 2004).

4.0 Conclusion

Both photochemical smog and ozone depletion are of great harm to human health and other living organisms’ .Reduction of ground-low ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide can reduce the effect of photochemical smog in the planet. Creating awareness of the effects of photochemical smog, the condition that that create it and preventive measures to the general public is of great significance. Moreover support of government initiatives to reduce air pollution, promote public transportation, improve bicycle paths and other measures will reduce the impact that citizen have on their community and surrounding environments. On the other hand the reduction of Chlorofluorocarbons (CFCs) will solve the problem of ozone depletion.


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