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Encyclopedia > Tropospheric Ozone
Seasonal average concentrations of tropospheric ozone in Dobson units over the period 1979 to 2000. In June to August photochemical ozone production causes very high concentrations over the East Coast of the USA and China.
Seasonal average concentrations of tropospheric ozone in Dobson units over the period 1979 to 2000. In June to August photochemical ozone production causes very high concentrations over the East Coast of the USA and China.

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, a constituent of smog. Many highly energetic reactions produce it, ranging from combustion to photocopying. Often laser printers will have a smell of ozone, which in high concentrations is toxic. Ozone is a powerful oxidizing agent readily reacting with other chemical compounds to make many possibly toxic oxides. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Dobson units (DU) are the standard way to express ozone amounts in the atmosphere. ... It has been suggested that Ozone generator be merged into this article or section. ... Atmosphere diagram showing the mesosphere and other layers. ... Atmosphere diagram showing stratosphere. ... The ozone layer is a part of the Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Many of the compounds which are dangerous to the environment can also be harmful to humans in the long-term range and come from mineral and fossil sources or are produced by humans themselves. ... It has been suggested that Haze be merged into this article or section. ... European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidizing agents Oxidizing agent placard An oxidizing agent (also called an oxidant or oxidizer) is A chemical compound that readily transfers oxygen atoms or A substance that gains electrons in a redox chemical reaction. ... Toxic redirects here, but this is also the name of a song by Britney Spears; see Toxic (song) Look up toxic and toxicity in Wiktionary, the free dictionary. ...


The troposphere extends to between 10 and 18 kilometers above the surface of the Earth and consists of many layers. Ozone is more concentrated above the mixing layer, or ground layer. Ground-level ozone, though less concentrated than ozone aloft, is more of a problem because of its health effects. Atmosphere diagram showing the mesosphere and other layers. ... This article is about Earth as a planet. ... Seasonal average concentrations of tropospheric ozone in Dobson units over the period 1979 to 2000. ...


Tropospheric ozone is a greenhouse gas and initiates the chemical removal of methane and other hydrocarbons from the atmosphere thus its concentration affects how long these compounds remain in the air. Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ... Methane is a chemical compound with the molecular formula CH4. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ...


Satellites can measure tropospheric ozone.[1][2] Measurements specifically of ground-level ozone require in situ monitoring technology. For other uses, see Satellite (disambiguation). ... In situ is a Latin phrase meaning in the place. ...

Contents

Formation

The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs), such as xylene, react in the atmosphere in the presence of sunlight. NOx and VOCs are called ozone precursors. Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these chemicals. Although these precursors often originate in urban areas, winds can carry NOx hundreds of kilometers, causing ozone formation to occur in less populated regions as well. Methane, a VOC whose atmosperic concentration has increased tremendously during the last century, contributes to ozone formation but on a global scale rather than in local or regional photochemical smog episodes. In situations where this exclusion of methane from the VOC group of substances is not obvious, the term Non-Methane VOC (NMVOC) is often used. Nitrogen has six different oxides: Nitric oxide (NO) Nitrous oxide (N2O) Nitrogen dioxide (NO2) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen pentoxide (N2O5) The term nitrogen oxide is imprecise and can be used to refer to any of these or to a mixture of them. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Volatile organic compounds (VOCs) are organic chemical compounds that have high enough vapour pressures under normal conditions to significantly vaporize and enter the atmosphere. ... The term xylenes refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. ...


The chemical reactions involved in tropospheric ozone formation are a series of complex cycles in which carbon monoxide and VOCs are oxidised to water vapour and carbon dioxide. The reactions involved in this process are illustrated here with CO but similar reactions occur for VOC as well. Oxidation begins with the reaction of CO with the hydroxyl radical. The hydrogen atom formed by this reacts rapidly with oxygen to give a peroxy radical HO2 Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ...

OH + CO → H + CO2
H + O2 → HO2

Peroxy radicals then go on to react with NO to give NO2 which is photolysed to give atomic oxygen and through reaction with oxygen a molecule of ozone: Photolysis refers to any chemical reaction in which a compound is broken down by light. ...

HO2 + NO → OH + NO2
NO2 + hν → NO + O
O + O2 → O3

The net effect of these reactions is:

CO + 2O2 → CO2 + O3

This cycle involving HOx and NOx is terminated by the reaction of OH with NO2 to form nitric acid or by the reaction of peroxy radicals with each other to form peroxides. The chemistry involving VOCs is much more complex but the same reaction of peroxy radicals oxidizing NO to NO2 is the critical step leading to ozone formation. The chemical compound nitric acid (HNO3), also known as aqua fortis and spirit of nitre, is an aqueous solution of hydrogen nitrate (anhydrous nitric acid). ... Peroxide has three distinct meanings: Colloquial meaning In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. ...


Health effects

Ozone is known to have the following health effects at concentrations common in urban air:

  • Irritation of the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest.
  • Reduced lung function, making it more difficult to breathe deeply and vigorously. Breathing may become more rapid and more shallow than normal, and a person's ability to engage in vigorous activities may be limited.
  • Aggravation of asthma. When ozone levels are high, more people with asthma have attacks that require a doctor's attention or use of medication. One reason this happens is that ozone makes people more sensitive to allergens, which in turn trigger asthma attacks.
  • Increased susceptibility to respiratory infections.
  • Inflammation and damage the lining of the lungs. Within a few days, the damaged cells are shed and replaced much like the skin peels after a sunburn. Animal studies suggest that if this type of inflammation happens repeatedly over a long time period (months, years, a lifetime), lung tissue may become permanently scarred, resulting in permanent loss of lung function and a lower quality of life.

A statistical study of 95 large urban communities in the United States found significant association between ozone levels and premature death. The study estimated that a one-third reduction in urban ozone concentrations would save roughly 4000 lives per year (Bell et. al, 2004). The Respiratory System Among four-legged animals, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... An allergen is any substance (antigen), most often eaten or inhaled, that is recognized by the immune system and causes an allergic reaction. ... Upper respiratory infections, commonly referred to the acronym URI, is the illness caused by an acute infection which involves the upper respiratory tract: nose, sinuses, pharynx, larynx, or bronchi. ...


Problem areas

The United States Environmental Protection Agency has developed an Air Quality index to help explain air pollution levels to the general public. 8-hour average ozone concentrations of 85 to 104 ppbv are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy" [3]. The EPA has designated over 300 counties of the United States, clustered around the most heavily populated areas (especially in California and the Northeast), as failing to comply with the National Ambient Air Quality Standards. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... EPA redirects here. ... Parts-per notation is a measure of concentration that is used where low levels of concentration are significant. ... The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency that apply for outdoor air throughout the country. ...


See also

The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency that apply for outdoor air throughout the country. ... It has been suggested that Ozone generator be merged into this article or section. ... Photochemical smog is the term to represent a multitude of chemical agents which are considered to be detrimental to the environment and health. ... Atmosphere diagram showing the mesosphere and other layers. ... Criteria air contaminants (CAC) are a group of air pollutants that cause smog, acid rain and other health hazards. ...

References

Michelle L. Bell; Aidan McDermott; Scott L. Zeger; Jonathan M. Samet; Francesca Dominici (2004). "Ozone and Short-term Mortality in 95 US Urban Communities, 1987-2000". Journal of the American Medical Association. 292, 2372-2378.


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


Wayne, Richard P (2000). Chemistry of Atmospheres (3rd Ed.). Oxford University Press. ISBN 0-19-850375-X


External links


  Results from FactBites:
 
Encyclopedia: Tropospheric ozone (1136 words)
) in the troposphere, is a pollutant, a constituent of smog.
Ozone (O3) in the troposphere, is a pollutant, a constituent of smog.
Tropospheric ozone is a greenhouse gas and initiates the chemical removal of methane and other hydrocarbons from the atmosphere thus its concentration affects how long these compounds remain in the air.
  More results at FactBites »

 
 

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