Ozone Layer Overview and Discovery

Ozone Layer Overview

• Ozone is a protective gaseous layer in the atmosphere, crucial for life on Earth.
• It filters harmful ultraviolet (UV) radiation from the sun, preventing sunburn, skin cancer, and eye cataracts.
• Composed of three oxygen atoms (O-O-O).
• Located in the stratosphere, approximately 10-30 miles from Earth's surface.

Ozone Layer Discovery

• Ozone's discovery was gradual, beginning in the late 1700s with oxygen's identification.
• Christian Schönbein discovered ozone in 1840 during electrical experiments.
• Sterry Hunt hypothesized that ozone was a modified form of oxygen.
• W.N. Hartley linked ozone to absorption of UV light in the 1870s.
• G.M.B. Dobson invented a spectrometer in the 1920s to measure atmospheric ozone levels, which is still used today.
• Dobson also noted seasonal variations.
• Sherwood Rowland and Mario Molina proposed the fluorocarbon-ozone theory in 1974.
• They demonstrated that CFCs could destroy ozone molecules, leading to the ban of CFCs in aerosol sprays starting in 1979.
• Rowland and Molina were awarded the Nobel Prize in 1995 for their work.
• The British Antarctic Survey reported a significant ozone hole over Antarctica in 1985.

Ozone Layer Structure and Distribution

• Ozone concentration in the stratosphere averages 12 parts per million (ppm).
• The Dobson Unit (DU) measures ozone layer "thickness." Global average density is around 300 DU.
• Ozone concentrations vary geographically based on seasonality, location, and wind.
• Ozone density is generally lower near the tropics and higher near the poles.
• The Brewer-Dobson circulation moves ozone from the tropics to higher latitudes.
• The ozone hole forms each spring over Antarctica due to increased UV light.

Ozone Creation and Destruction

• Ozone is created through chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs), initiated by UV light.
• Ground-level ozone formation is often associated with urban areas, factories, and sunny days, causing health problems.
• Ozone is destroyed through reactions with chlorofluorocarbons (CFCs).
• CFCs, used in refrigerants and other products, react with ozone in the presence of UV light, breaking down ozone molecules. One CFC can destroy thousands of ozone molecules.
• Nitrogen dioxide (NO2) can also deplete ozone through UV-induced reactions.

Ozone Importance and Depletion

• The ozone layer protects life from harmful UV radiation, reducing incidences of skin cancer and cataracts in humans.
• UV radiation can also damage plants and impact ecosystems.
• Ozone depletion leads to increased UV exposure on the Earth's surface.
• From the 1950s to the 1980s, CFCs were extensively used as refrigerants, leading to ozone depletion.
• Scientific observations in the 1970s and 1980s revealed the formation of an ozone hole over Antarctica.

Efforts to Save the Ozone Layer

• The Montreal Protocol (1987), signed by 24 nations, aimed to drastically reduce CFC production.
• Subsequent agreements and actions further protected the ozone layer.
• The Montreal Protocol has nearly 200 global signatories.
• CFC use declined by 95% from the 1980s, following the protocol.
• The ozone layer is projected to recover to pre-1980 levels by approximately 2065.

Ozone in the Troposphere and its Effects

• Ground-level ozone (smog) can be harmful to human health, causing respiratory problems.
• The Environmental Protection Agency (EPA) sets standards for ozone concentrations to protect public health.
• Elevated ozone concentrations are often observed in urban areas, near factories, and during periods of high UV radiation.

Ozone and Astronomy Implications

• The ozone layer blocks UV radiation, making satellite observations crucial for astronomy.
• Satellites positioned above the layer permit precise measurement of UV radiation, important for studying stars and galaxies.