Question

Read “The Ozone Hole” and answer the question below.

Use examples from the article to explain one positive and one negative effect that chemistry has had on society.

What is Ozone?
Ozone is a gas made of oxygen atoms that occurs both in the Earth's upper atmosphere and at ground level. Ozone can be "good" or "bad" for your health and the environment depending on its location in the atmosphere. Ozone occurs in the troposphere, the atmospheric layer closest to the Earth’s surface. Here, ground-level, or "bad," ozone is an air pollutant that is harmful to breathe and it damages crops, trees, and other vegetation. It is a main ingredient of urban smog. Ozone also occurs in the stratosphere, the layer directly above the troposphere. Stratospheric, or "good," ozone protects life on Earth from the Sun's harmful ultraviolet (UV) rays.

Ozone is produced naturally in the stratosphere, but this area of “good” ozone is gradually being destroyed by manmade chemicals called ozone-depleting substances. These chemicals include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. They are found in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants. Once released into the air, ozone-depleting substances degrade very slowly. They often remain in the atmosphere for years, moving from the troposphere to the stratosphere. Once they enter into the stratosphere, they are broken down by the intensity of the Sun's UV rays and release chlorine and bromine molecules, which destroy the "good" ozone.

Holes in the ozone layer allow harmful ultraviolet rays to reach Earth’s plants and animals in excess. Too much ultraviolet light can result in eye damage like cataracts, immune system damage, skin cancer, DNA damage, and phytoplankton reduction in the oceans.

Ozone Depletion History
In cold areas such as Antarctica, there are stratospheric cloud ice particles that are not present at warmer latitudes. Reactions occur on the surface of the ice particles that accelerate the ozone destruction caused by stratospheric chlorine. Temperatures hover around or below negative 80 degrees celsius for much of the winter and extremely low Antarctic temperatures cause cloud formation in the relatively "dry" atmosphere. These Polar Stratospheric Clouds (P S C's) are composed of ice crystals that provide the surface for a multitude of reactions, many of which speed the degradation of ozone molecules.
Ozone depletion history began in the late 1950s with ground-based ozone measurements from Antarctica taken by international collaboration efforts. In 1974, Mario Molina and Frank Sherwood Rowland published an article in Nature on the developing threat to the ozone layer from the use of chlorofluorocarbons (CFCs), gaseous compounds used as refrigerants, aerosol propellants, solvents, and in foam. The study estimated that the ozone layer would be depleted by CFCs by about seven percent within 60 years. Based on such studies, the US banned CFCs in aerosol sprays in 1978. Also in 1978, the first comprehensive global measurements began with the Nimbus-7 satellite, which carried the total ozone mapping spectrometer (TOMS). Testing continued through the 1990s.

Mario Molina (left) and Frank Sherwood Rowland (right).
Photos by Janwikifoto and Markus Possels
Mario Molina (left) and Frank Sherwood Rowland (right) received the 1995 Nobel Prize in Chemistry on their work on ozone depletion.

CONTINUED
Edgenuity

Answer 1

Negative effect — harmful chemicals destroyed the ozone layer:
- Chemists created ozone-depleting substances (CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, methyl chloroform) that were widely used as refrigerants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants.
- Once released, these compounds persist, rise to the stratosphere, and are broken down by UV light to release chlorine and bromine atoms that destroy “good” stratospheric ozone.
- The resulting ozone thinning (and Antarctic “ozone holes” enhanced by reactions on polar stratospheric cloud ice particles) lets more UV reach Earth, causing cataracts, immune-system damage, skin cancer, DNA damage, and reductions in ocean phytoplankton.

Positive effect — chemistry enabled diagnosis and solutions that protect people and the environment:
- Chemical research by Mario Molina and F. Sherwood Rowland (1974) identified the link between CFCs and ozone depletion; their work led to scientific awareness and later recognition (1995 Nobel Prize).
- That research and subsequent monitoring (for example, the Nimbus-7 satellite’s total ozone mapping spectrometer) made the problem measurable and visible to policymakers.
- As a direct result, governments acted — for example, the U.S. banned CFCs in aerosol sprays in 1978 — showing how chemical science can diagnose risks and drive policies and technologies that reduce harm.