6.02 Ozone

Substantial evidence demonstrates that ozone loss is not connected to global warming.

Although loss of ozone does allow more of the sun's radiation to reach us on Earth, global warming is caused by greater amounts of greenhouse gases, including carbon dioxide and ozone, in the troposphere.

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ClO + O → Cl + O2 With the addition of a free atom of oxygen, chlorine oxide decomposes again.

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ClO + O → Cl + O2 With the addition of a free atom of oxygen, chlorine oxide decomposes.

Can smell ozone after rain because it is generated by

lighting. In the lower atmosphere you can smell it, in the upper atmosphere it protects from UV radiation.

More specifically, nitrogen oxide (NO) reacts with

oxygen gas (O2) to form nitrogen dioxide (NO2), which forms a brownish haze that is characteristic of photochemical smog. 2NO + O2 → 2NO2

The free atom of oxygen (O) bonds to

oxygen gas (O2) to form ozone, which is considered a pollutant in the troposphere. O + O2 → O3

Where do these ozone-depleting substances come from? ODS are removing

ozone from the stratosphere and have been for decades.

Earth is shrouded by a layer of

ozone in the stratosphere that screens 99 percent of the sun's ultraviolet radiation. Life on Earth could not exist in the same way without this effect. Human beings and other animals would suffer burns, cancer, and mutations.

In the ocean, the most concerning effect of stratospheric ozone depletion is its effect on

phytoplankton. As the base of most marine food webs, phytoplankton provides energy to all other organisms. Exposure to additional ultraviolet radiation inhibits their ability to photosynthesize, particularly near the surface. This means that ozone depletion leads to the destruction of marine food webs.

The Clean Air Act also provides

protection of the stratospheric ozone by phasing out production and consumption of all ozone-depleting substances within the United States. This protection was added in a 1990 amendment.

Ozone is also found in the

stratosphere where it is important in protecting us from ultraviolet radiation from the sun. The EPA has a slogan, "Good up high, bad nearby," to describe where ozone is helpful (the stratosphere) and where it is harmful (the troposphere).

You know that ozone is found in the

troposphere. You know that it can be created in small amounts naturally by a lightning storm, but that it is also considered a pollutant and is the primary ingredient in smog. Ozone can harm vegetation by hurting its ability to photosynthesize, as well as cause respiratory illnesses in human beings.

Then nitrogen dioxide (NO2) reacts with

ultraviolet light to form nitrogen oxide and oxygen. NO2 + UV light → NO + O

Steps

Reactions Explanations

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Cl + O → ClO + O2 A free atom of chlorine combines with ozone to produce chlorine oxide and oxygen gas.

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Cl + O3 → ClO + O2 Here the free atom of chlorine and ozone produce chlorine oxide and oxygen gas.

There are a number of respiratory effects of having too much ozone in the troposphere:

tightness in the chest, reduced lung function, damage to cells in the lung, increased susceptibility to lung infection, aggravation of asthma

Cl + O → ClO + O2

A free atom of chlorine combines with ozone to produce chlorine oxide and oxygen gas.

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CCl3F + UV light → CCl2F + Cl Here a CFC decomposes, leaving a free atom of chlorine as a product.

CCl3F + UV light → CCl2F + Cl

Here a CFC decomposes, leaving a free atom of chlorine as a product.

Cl + O3 → ClO + O2

Here the free atom of chlorine and ozone produce chlorine oxide and oxygen gas.

1.

How is ozone important in the stratosphere? Answer: Ozone protects human beings from ultraviolet radiation from the sun.

The Ozone Hole

In 1974, scientists Mario Molina and F. Sherwood Rowland hypothesized that CFCs could react with ozone in the stratosphere. This became a very active area of research, and by the 1980s scientists began to notice that the ozone layer was thinning substantially over the South Pole; the thinning started in August and peaked in October. The greatest hole in the ozone layer appeared in the spring in Antarctica in the southern hemisphere. Scientists hypothesized that over the long winter in Antarctica, conditions are created known as a "polar vortex," a jet stream of extremely cold air, which blocks warmer air from entering in the complete darkness. This vortex creates polar stratospheric clouds, which are extremely cold, and become a location for CFCs to connect to the ice crystals. Then, with the arrival of abundant sunlight in the spring, CFCs are released from the clouds and the ozone level decreases as CFCs break into chlorine, which decomposes ozone. The depletion of ozone allows more ultraviolet radiation to reach Earth.

The decrease in ozone depletion is due in large part to the

Montreal Protocol, one of the great environmental success stories. In 1987, The Montreal Protocol on Substances that Deplete the Ozone Layer (often referred to simply as the Montreal Protocol) was adopted by the United States and over 180 other countries. The dramatic and clear evidence of ozone depletion convinced governments to seek alternatives for ozone-depleting substances as well as work together in unprecedented cooperation. The primary provisions of the agreement phased out production and consumption of ozone-depleting substances, including chlorofluorocarbons, halons, carbon tetrachloride, and methyl chloroform, with the understanding that these compounds deplete the ozone in the stratosphere, which protects the planet from ultraviolet radiation. Compliance of the Montreal Protocol is considered excellent among countries that signed the agreement.

Ozone depletion causes adverse health effects in human beings.

More ultraviolet radiation reaches Earth when ozone has been depleted, which contributes to an increase in melanoma, a type of skin cancer. According to the EPA, since 1990, the risk of developing melanoma has more than doubled. Ozone also affects some terrestrial plants, such as soybeans, and can decrease overall crop yield.

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What are the sources of ozone in the troposphere? Answer: Sources of ozone include industrial facilities and automobile emissions, which contribute NOx and VOCs, which create a series of reactions that produce ozone under the influence of sunlight and heat.

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Which reactions describe the formation of ozone in the troposphere? Answer: 2NO + O2 → 2NO2; NO2 + UV light → NO + O; O + O2 → O3

2.

Why is the Montreal Protocol important? Answer: The Montreal Protocol is an international agreement to phase out production and consumption of ozone-depleting substances.

ClO + O → Cl + O2

With the addition of a free atom of oxygen, chlorine oxide decomposes again.

ClO + O → Cl + O2

With the addition of a free atom of oxygen, chlorine oxide decomposes.

All of the substances were part of

aerosol propellants, pesticides, coolants, foaming agents, solvents, and fire extinguishers. They were assumed to be completely inert since the 1920s when they began to be used profusely. CFCs remain intact once they are released as they travel from the troposphere to the stratosphere. Only when they reach the stratosphere can they be broken down in the reactions described above.

Montreal Protocol:

an international agreement to reduce production and consumption of ozone-depleting substances

These ODS include:

chlorofluorocarbons (CFCs), propellants, and blowing agents, hydrochlorofluorocarbons (HCFCs), also propellants and blowing agents (and used to replace CFCs), halons, used in fire protection, methyl bromide, a soil fumigant, carbon tetrachloride, a solvent, methyl chloroform, a cleaning agent

Under the Montreal Protocol, the provisions are different for

developed and developing countries. Because developing countries have fewer resources with which to resource substitutes for ozone-depleting substances, they have been allocated a slightly longer timeframe with which to reduce consumption and production. The Montreal Multilateral Fund provides financial help to countries phase out CFCs.

there is too much ozone in the troposphere, but there is too little ozone in the stratosphere. Within the stratosphere, ozone is destroyed by ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), which are also known as freon and used to be used in air conditioning and cooling systems. With ultraviolet radiation, CFCs (such as CCl3F) break down to produce

free chlorine atoms (Cl), which, in turn, break down ozone O3.

As a pollutant in the troposphere, ozone is the product of

gases (NOx) from emissions from cars, power plants, chemical plants, and other industrial facilities mixing with volatile organic compounds (VOCs) under the influence of heat and sunlight. These emissions of nitrogen oxides (NOX) and VOCs react with heat and sunlight to form ozone.