Air pollution
-
Ozone is not directly emitted by car engines or by industrial operations. These sources emit hydrocarbons and nitrogen oxides that react with sunlight to form ozone directly at the source of the pollution being emitted and in the atmosphere's boundary layer (1 to 3 km altitude). The mix of hydrocarbons, nitrogen oxides, and ozone are the major components of smog that frequently occurs in urban and suburban areas. Recent satellite maps of nitrogen dioxide (NO2) clearly show the worldwide distribution of polluted regions associated with industrial activity (automobiles, factories, and fossil fuel power generation).
There is a great deal of evidence to show that ozone at the earth's surface can harm lung function and irritate the respiratory system [3]. Ozone has been found to convert cholesterol in the blood stream to plaque (which causes hardening and narrowing of arteries). This cholesterol product has also been implicated in Alzheimer's disease, suggesting a link between the inflammatory response associated with head injury and Alzheimer's. Air quality guidelines such as those from the World Health Organization are based on detailed studies of what levels can cause measurable health effects.
There is also evidence of significant reduction in agricultural yields due to increased ground-level ozone which interferes with photosynthesis and stunts overall growth of some plant species.[4][5]
Although ozone was present at ground level before the industrial revolution, peak concentrations are far higher than the pre-industrial levels and even background concentrations well away from sources of pollution are substantially higher.[6][7]
Ozone reacts directly with some hydrocarbons such as aldehydes and thus begins their removal from the air, but the products of ozonolysis are themselves key components of smog. Ozone photolysis by UV light leads to production of the hydroxyl radical and this plays a part in the removal of hydrocarbons from the air, but is again a step in the creation of components of smog such as peroxyacyl nitrates which are powerful eye irritants. Ultimately, ozone is one component of smog which is harmful in itself and contributes both to the production and ultimate removal of other air pollutants.
Industrial production
Industrially, ozone is produced with short wavelength ultraviolet radiation from a mercury vapor lamp or the application of a high voltage electrical field in a process called cold or corona discharge. The cold discharge apparatus consists of two metal plates separated by an air gap and a high dielectric strength electrical insulator such as borosilicate glass or mica. A high voltage alternating current is applied to the plates and the ozone is formed in the air gap when O2 molecules disassociate and recombine into O3. A faint corona may be present in the air gap, but the voltage is maintained below that which would cause punch-through of the insulator with subsequent arcing and plasma formation. In the laboratory ozone can be produced by electrolysis using a 9 volt battery, a pencil graphite rod cathode, a platinum wire anode and a 3M sulfuric acid electrolyte.[8] The half cell reactions taking place are:
- 3H2O → O3 + 6H+ + 6e− ΔEo = − 1.53 V
- 6H+ + 6e− → 3H2 ΔEo = 0 V
- 2H2O → O2 + 4H+ + 4e− ΔEo = −1. 23 V
So that in the net reaction three equivalents of water are converted into one equivalent of ozone and three equivalents of hydrogen. Oxygen formation is a competing reaction...
Chemistry
Ozone will oxidize metals (except gold, platinum, and iridium) to oxides of the metals in their highest oxidation state:
- 2 Cu2+ + 2 H+ + O3 → 2 Cu3+ + H2O + O2
Ozone converts oxides to peroxides:
- SO2 + O3 → SO3 + O2
It also oxidizes oxides to oxides of higher oxidation number:
- NO + O3 → NO2 + O2
The above reaction is accompanied by chemiluminescence. The NO2 can be further oxidized:
- NO2 + O3 → NO3 + O2
The NO3 formed can react with NO2 to form N2O5:
- NO2 + NO3 → N2O5
Ozone reacts with carbon to form carbon dioxide, even at room temperature:
- C + 2 O3 → CO2 + 2 O2
Ozone does not react with ammonium salts but it reacts with ammonia to form ammonium nitrate:
- 2 NH3 + 4 O3 → NH4NO3 + 4 O2 + H2O
Ozone reacts with sulfides to make sulfates:
- PbS + 4 O3 → PbSO4 + 4 O2
Sulfuric acid can be produced from ozone, either starting from elemental sulfur or from sulfur dioxide:
- S + H2O + O3 → H2SO4
- 3 SO2 + 3 H2O + O3 → 3 H2SO4
All three atoms of ozone may also react, as in the reaction with tin(II) chloride and hydrochloric acid:
- 3 SnCl2 + 6 HCl + O3 → 3 SnCl4 + 3 H2O
In the gas phase, ozone reacts with hydrogen sulfide to form sulfur dioxide:
- H2S + O3 → SO2 + H2O
In an aqueous solution, however, two competing simultaneous reactions occur, one to produce elemental sulfur, and one to produce sulfuric acid:
- H2S + O3 → S + O2 + H2O
- 3 H2S + 4 O3 → 3 H2SO4
Iodine perchlorate can be made by treating iodine dissolved in cold anhydrous perchloric acid with ozone:
- I2 + 6 HClO4 + O3 → 2 I(ClO4)3 + 3 H2O
Solid nitryl perchlorate can be made from NO2, ClO2, and O3 gases:
- 2 NO2 + 2 ClO2 2 O3 → 2 NO2ClO4 + O2
Ozone can be used for combustion reactions and combusting gases in ozone provides higher temperatures than combusting in dioxygen (O2). Following is a reaction for the combustion of carbon subnitride:
- 3 C4N2 + 4 O3 → 12 CO + 3 N2
Ozone can react at cryogenic temperatures. At 77 K (-196 °C), atomic hydrogen reacts with liquid ozone to form a hydrogen superoxide radical, which dimerizes[9]:
- H + O3 → HO2 + O
- 2 HO2 → H2O4
Ozonides can be formed, which contain the ozonide anion, O3-. These compounds are explosive and must be stored at cryogenic temperatures. Ozonides for all the alkali metals are known. KO3, RbO3, and CsO3 can be prepared from their respective superoxides:
- KO2 + O3 → KO3 + O2
Although KO3 can be formed as above, it can also be formed from potassium hydroxide and ozone:[10]
- 2 KOH + 5 O3 → 2 KO3 + 5 O2 + H2O
NaO3 and LiO3 must be prepared by action of CsO3 in liquid NH3 on an ion exchange resin containing Na+ or Li+ ions:[11]
- CsO3 + Na+ → Cs+ + NaO3
Treatment with ozone of calcium dissolved in ammonia leads to ammonium ozonide and not calcium ozonide:[12]
- 3 Ca + 10 NH3 + 6 O3 → Ca•6NH3 + Ca(OH)2 + Ca(NO3)2 + 2 NH4O3 + 2 O2 + H2
Ozone can be used to remove manganese from the water, forming a precipitate which can be filtered:
- 2 Mn2+ + 2 O3 + 4 H2O → 2 MnO(OH)2 (s) + 2 O2 + 4 H+
Ozone will also turn cyanides to the one thousand times less toxic cyanates:
- CN- + O3 → CNO- + O2
Finally, ozone will also completely decompose urea:[13]
- (NH2)2CO + O3 → N2 + CO2 + 2 H2O
Applications
Industrial applications
Ozone can be used for bleaching substances and for killing bacteria. Many municipal drinking water systems kill bacteria with ozone instead of the more common chlorine. Ozone does not form organochlorine compounds, but it also does not remain in the water after treatment, so some systems introduce a small amount of chlorine to prevent bacterial growth in the pipes, or may use chlorine intermittently, based on results of periodic testing. Where electrical power is abundant, ozone is a cost-effective method of treating water, as it is produced on demand and does not require transportation and storage of hazardous chemicals. Once it has decayed, it leaves no taste or odor in drinking water.
Industrially, ozone or ozonated water is used to:
- disinfect water before it is bottled,
- deodorize air and object, such as after a fire
- kill bacteria on food-contact surfaces
- scrub yeast and mold spores from the air in food processing plants
- wash fresh fruits and vegetables to kill yeast, mold and bacteria
- chemically attack contaminants in water (iron, arsenic, hydrogen sulfide, nitrites, and complex organics lumped together as "color"),
- provide an aid to flocculation (a process of agglomeration of molecules, which aids in filtration... this is where the iron and arsenic are removed),
- clean and bleach fabrics (the latter use is patented),
- assist in processing plastics to allow adhesion of inks,
- age rubber samples to determine the useful life of a batch of rubber.
- Used in surface water treatment plants to eradicate bacteria such as Giardia and Cryptosporidium. This process is known as ozonation.
Ozone is a reagent in many organic reactions in the laboratory and in industry. Ozonolysis is the cleavage of an alkene to carbonyl compounds.
Consumer applications
Ozonated water can be used to sanitize food, water, and surfaces in the home. According to the FDA, it is "amending the food additive regulations to provide for the safe use of ozone in gaseous and aqueous phases as an antimicrobial agent on food, including meat and poultry." Ironically, while ozone is considered an atmospheric pollutant, it can actually reduce pollutants like pesticides in fruits and vegetables.[14]
Pharmaceutical applications
Ozone, along with hypochlorite ions, is naturally produced by white blood cells and the roots of marigolds as a means of destroying foreign bodies. When ozone breaks down it gives rise to oxygen free radicals, which are highly reactive and damage or destroy most organic molecules.
Ozone has a number of medical uses. It can be used to affect the body's antioxidant-prooxidant balance, since the body usually reacts to its presence by producing antioxidant enzymes. Many hospitals in the U.S. and around the world use large ozone generators to decontaminate operating rooms between surgeries. The rooms are cleaned and then sealed airtight before being filled with ozone which effectively kills or neutralizes all remaining bacteria.
Ozone therapy has blossomed into a thriving field of alternative medicine, and there are a host of claimed applications above and beyond what has actually been verified by studies.
In the United States ozone therapy is illegal, as the Food and Drug Administration (FDA) has not approved its use on humans. Medical ozone therapy is recognized in Bulgaria, Cuba, Czech Republic, France, Germany, Israel, Italy, Mexico, Romania and Russia. It is currently used legally in 16 Nations. At least 12 states in the USA (AK, AZ, CO, GA, MN, NY, NC, OH, OK, OR, SC and WA) have passed legislation to ensure that alternative therapies are available to consumers. Physicians in those states can legally use ozone as an alternative treatment in their practice without fear of prosecution.
At least one death has been attributed to application of ozone through insufflation in the U.S.[citation needed] "Air cleaners" which produce "activated oxygen", i.e., ozone, are often sold in the U.S. nonetheless. See Air ioniser.
Other uses
During the 1992 U.S. Presidential election, George H.W. Bush referred to his opponents Bill Clinton and Al Gore as "Bozo and Ozone", respectively, the latter in connection with Gore's well known stance on environmental issues.
Ozone is also popularly used in spas or hot tubs instead of Chlorine or Bromine for keeping the water free of bacteria. Ozone gas is created by an ultraviolet light bulb or corona discharge chip and injected into the plumbing system.
Ozone is also widely used in treatment of water in aquaria and fish ponds. Its use can minimises bacterial growth control parasites and removes or reduce "yellowing" of the water. As the Ozone rapidly decomposes, at correctly controlled levels the application has no effect on the fish.
Health effects
A team headed by Dr. Paul Wentworth Jr. of the Department of Chemistry at the Scripps Research Institute has shown strong evidence linking the antibody-catalyzed water-oxidation pathway of the human immune response to the production of ozone. Moreover, it is believed that the powerful oxidizing properties of ozone may be a contributing factor of inflammation.
Ozone has also been proven to form specific, cholesterol-derived metabolites that are thought to facilitate the build-up and pathogenesis of atherosclerotic plaques (A form of heart disease). These metabolites have been confirmed as naturally occuring in human atherosclerotic arteries and are categorized into a class of secosterols termed “Atheronals”, generated by ozonolysis of cholesterol's double bond to form a 5,6 secosterol as well as a secondary condensation product via aldolization.[15][16]
See also
References
- ^ Today in Science History. Retrieved on 2006-05-10.
- ^ Ozone FAQ. Global Change Master Directory. Retrieved on 2006-05-10.
- ^ WHO-Europe reports: Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
- ^ Rising Ozone Levels Pose Challenge to U.S. Soybean Production, Scientists Say. NASA Earth Observatory (2003-07-31). Retrieved on 2006-05-10.
- ^ Mutters, Randall (March 1999). Statewide Potential Crop Yield Losses From Ozone Exposure. California Air Resources Board. Retrieved on 2006-05-10.
- ^ Tropospheric Ozone in EU - The consolidated report. European Environmental Agency (1998). Retrieved on 2006-05-10.
- ^ Atmospheric Chemistry and Greenhouse Gases. Intergovernmental Panel on Climate Change. Retrieved on 2006-05-10.
- ^ Ibanez, Jorge G., Rodrigo Mayen-Mondragon and M. T. Moran-Moran (October 2005). "Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 7: Microscale Production of Ozone". Journal of Chemical Education 82: 1546. Retrieved on 2006-05-10.
- ^ Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 44-49
- ^ Housecroft & Sharpe, 2005. "Inorganic Chemistry." pg 439
- ^ Housecroft & Sharpe, 2005. "Inorganic Chemistry." pg 265
- ^ Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 44-49
- ^ Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 259, 269-270
- ^ lotus Sanitizes Food without Chemicals (2000). Retrieved July 24, 2006.
- ^ Paul Wentworth (November 2003). Evidence for Ozone Formation in Human Atherosclerotic Arteries. Retrieved on 2006-08-03.
- ^ Error on call to template:cite web: Parameters url and title must be specified.
- Seinfeld, John H.; Pandis, Spyros N (1998). Atmospheric Chemistry and Physics - From Air Pollution to Climate Change. John Wiley and Sons, Inc. ISBN 0-471-17816-0
- Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.). Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
External links