EPA Questions and Answers on Ozone Depletion

8/3/2019 EPA Questions and Answers on Ozone Depletion

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http://www.epa.gov/ozone/science/q_a.html#q1Last updated on Thursday, August 19, 2010

Questions and Answers on Ozone Depletiony What is the ozone layer and why is it important? y H ow does ozone depletion occur? y H ow do we know that natural sources are not responsible for ozone

depletion? y What is being done about ozone depletion? y I s there general agreement among scientists on the science of

ozone depletion? y Will the ozone layer recover? Can we make more ozone to fill in the

hole?

1. What is the ozone layer and why is it important?

The ozone layer is a concentration of ozone molecules in the

stratosphere . About 90% of the planet's ozone is in the ozone layer.

The layer of the Earth's atmosphere that surrounds us is called the

troposphere . The stratosphere , the next higher layer, extends about

10-50 kilometers above the Earth's surface. Stratospheric ozone is a

naturally-occurring gas that filters the sun's ultraviolet (UV) radiation.

A diminished ozone layer allows more radiation to reach the Earth's

surface. For people, overexposure to UV rays can lead to skin cancer,

cataracts, and weakened immune systems. I ncreased UV can also

lead to reduced crop yield and disruptions in the marine food chain.

UV also has other harmful effects .

2. How does ozone depletion occur?

I t is caused by the release of chlorofluorocarbons (CFCs) ,

hydrofluorocarbons ( H CFCs) , and other ozone-depleting substances

(ODS) , which were used widely as refrigerants, insulating foams, and

solvents. The discussion below focuses on CFCs, but is relevant to all

ODS. Although CFCs are heavier than air , they are eventually carried

into the stratosphere in a process that can take as long as 2 to 5

years. Measurements of CFCs in the stratosphere are made from

balloons, aircraft, and satellites.

When CFCs and H CFCs reach the stratosphere, the ultraviolet

radiation from the sun causes them to break apart and release

chlorine atoms which react with ozone, starting chemical cycles of

ozone destruction that deplete the ozone layer. One chlorine atom

can break apart more than 100,000 ozone molecules.


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Other chemicals that damage the ozone layer include methyl bromide

(used as a pesticide), halons (used in fire extinguishers), and methyl

chloroform (used as a solvent in industrial processes for essential

applications). As methyl bromide and halons are broken apart, they

release bromine atoms, which are 60 times more destructive to ozone

molecules than chlorine atoms.

3. How do we know that natural sources are not responsible for ozone depletion?

While it is true that volcanoes and oceans release large amounts of

chlorine , the chlorine from these sources is easily dissolved in water

and washes out of the atmosphere in rain. I n contrast, CFCs are notbroken down in the lower atmosphere and do not dissolve in water.

The chlorine in these human-made molecules does reach the

stratosphere. Measurements show that the increase in stratospheric

chlorine since 1985 matches the amount released from CFCs and

other ozone-depleting substances produced and released by human

activities.

4. What is being done about ozone depletion?

I n 1978, the use of CFC propellants in spray cans was banned in theU.S. I n the 1980s, the Antarctic " ozone hole " appeared

and an international science assessment more strongly linked the

release of CFCs and ozone depletion. I t became evident that a

stronger worldwide response was needed. I n 1987, the Montreal

Protocol was signed and the signatory nations committed themselves

to a reduction in the use of CFCs and other ozone-depleting

substances.

Since that time, the treaty has been amended multiple times to

accelerate the phaseout of CFCs, H CFCs, and other ozone depletingsubstances. Today, over 190 countries have ratified the treaty. For

over a decade the production of CFCs has been banned, with limited

exceptions for essential uses . The next step in the elimination of

ozone depleting substances occurs in 2010 when EPA will ban the

production of the most harmful H CFCs . This production phaseout is


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possible because of efforts to ensure that there are substitute

chemicals and technologies for the compounds being phased out.

EPA coordinates numerous regulatory programs designed to help the

ozone layer and continues to be active in developing international

ozone protection policies. I ndividuals can also help, primarily by

ensuring that technicians working on air conditioning and

refrigeration equipment are certified by EPA, that refrigerants are

recaptured and not released, and by educating themselves about the

issue of ozone depletion.

5. Is there general agreement among scientists on the science of ozone depletion?

Yes, Under the sponsorship of the UN Environment Programme

(UNEP) and the World Meteorological Organization (WMO) , thescientific community issues periodic reports on the science of ozone

depletion. Over 300 scientists worldwide drafted and reviewed the

most recent analysis, WMO/UNEP Scientific Assessment of Ozone

Depletion: 2006 .

6. Will the ozone layer recover? Can we make more ozone to fill in the hole?

Provided that we stop producing ozone-depleting substances , ozone

will be created through natural processes that should return the

ozone layer to normal levels by about 2050. I t is very important thatthe world comply with the Montreal Protocol; delays in ending

production could result in additional damage and prolong the ozone

layer's recovery.


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R equired Levels of Evacuation for AppliancesExcept for Small Appliances, MVACS, and MVAC-likeAppliances

Type of Appliance

Inches of MercuryVacuum* UsingEquipment Manufactured:

Before Nov.15, 1993

On or afterNov. 15,

1993

H CFC-22 appliance** normally containing less than 200 poundsof refrigerant 0 0

H CFC-22 appliance** normally containing 200 pounds or moreof refrigerant 4 10

Other high-pressure appliance** normally containing less than200 pounds of refrigerant (CFC-12, -500, -502, -114) 4 10

Other high-pressure appliance** normally containing 200pounds or more of refrigerant (CFC-12, -500, -502, -114) 4 15

Very H igh Pressure Appliance (CFC-13, -503) 0 0

Low-Pressure Appliance (CFC-11, H CFC-123) 25 25 mmH g

absolute

* Relative to standard atmospheric pressure of 29.9" H g ** Or isolated component of such an

appliance

EPA Questions and Answers on Ozone Depletion

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