The Atmosphere: Structure, Composition, and Ozone Depletion Guide

Oxygen Provision: The atmosphere provides the suurstof (oxygen) necessary for breathing, which is essential for almost all life forms on Earth.
Temperature Regulation: It regulates global temperature by absorbing dangerous radiant energy and solar radiation.
Protective Blanket: The atmosphere forms a protective layer over the Earth. It heats the planet to habitable levels while shielding the surface from harmful ultraviolet (UV) rays via the ozone layer.
Hydrological Cycle: It facilitates moisture and the water cycle (hidrologiese siklus), which is the driver for weather patterns.

Gaseous Elements (Gasse):
- Nitrogen: $78\%$
- Oxygen: $21\%$
- Argon: $0.9\%$
- Carbon Dioxide ( $CO_2$ ): $0.037\%$
Solid Components (Soliede): Includes dust (stof), salt crystals, and ice crystals (ys kristalle).
Liquid Components (Vloeistof): Present in the form of clouds (wolke).
Physical Properties: A critical property (eienskap) of the atmosphere is that it can be compressed. This allows for an increase in pressure (verhooding in druk) or a decrease in pressure (verminderings in druk) depending on altitude and air density.

Troposphere:
- Altitude: $0$ to approximately $10-15\,km$ .
- Contains the highest air density and the Earth's surface features such as Mt. Everest.
- The boundary at the top is the Tropopause.
Stratosphere:
- Altitude: Approximately $10\,km$ to $50\,km$ .
- Contains the Maximum Ozone concentration, which helps prevent radiation from reaching the surface.
- The boundary at the top is the Stratopause.
Mesosphere:
- Altitude: Approximately $50\,km$ to $80/90\,km$ .
- This layer is characterized by air density decreasing further and is the region where meteors typically burn up.
- The boundary at the top is the Mesopause.
Thermosphere:
- Altitude: Extends from $80/90\,km$ upwards to approximately $140\text{ miles}$ ( $\approx 225\,km$ ).
- Features include the Aurora and very high temperatures due to the absorption of radiant energy.
Altitudinal Relationship:
- Air Density: Decreases continuously as height increases.
- Pressure: Decreases as altitude increases.
- Temperature: Measured on a scale from approximately $-100^{\circ}C$ to $50^{\circ}C$ within these layers, with various inversions occurring at the boundaries.

Definition: A form of oxygen consisting of three atoms ( $O_3$ ).
The Dual Nature of Ozone:
- Good Ozone: Found in the stratosphere. It has the unique ability to reflect ultraviolet (UV) radiation, preventing it from entering the lower atmosphere and reaching the Earth's surface.
- Bad Ozone: Found in the troposphere. It behaves as a greenhouse gas (kweekhuisgas) and contributes to the increase of atmospheric temperature.
Formation Process (Vorming van osoon):
1. UV Radiation hits an oxygen molecule ( $O_2$ ).
2. The molecule is split (verdeel) into two separate oxygen atoms ( $O + O$ ).
3. Each individual oxygen atom collides and combines with a remaining oxygen molecule ( $O_2$ ).
4. This reaction results in the creation of an ozone molecule ( $O_3$ ).

Primary Pollutants:
- CFCs (Chlorofluorocarbons): Historically found in refrigerants (verkoelingsmiddels), aerosol sprays (spuitkannetjies), air conditioners, and industrial cleaning materials.
- HCFCs: Hydrochlorofluorocarbon gases used in aerosols, refrigerants, and solvents.
- Halons: Found in fire extinguishers.
- Methyl Bromide: Used in pesticides.
Chemical Mechanism of Ozone Layer Destruction:
1. CFCs and other pollutants are released into the troposphere and eventually rise to collect in the stratosphere ( $10-50\,km$ ).
2. UV rays split a chlorine ( $Cl$ ) atom away from the CFC molecule.
3. The free chlorine atom reacts with an ozone molecule ( $O_3$ ) and breaks it apart.
4. The chlorine atom binds with one oxygen atom to form Chlorine Monoxide ( $ClO$ ), leaving behind an oxygen molecule ( $O_2$ ).
5. This process reduces the number of ozone molecules, causing the layer to become thinner and eventually allowing "holes" to develop.

Human Health Impacts:
- Formation of cataracts in the eyes.
- Cause of premature aging of the skin and increased risk of skin cancer (velkanker).
- Weakening of the body's immune system (immuunstelsel).
Environmental Impacts:
- Interruption of photosynthesis, which leads to reduced crop yields (oesopbrengste) and unhealthy forest systems.
- Reduction of phytoplankton, which negatively affects all marine life food chains.
Climate Impact: Ozone in the troposphere acts as a greenhouse gas, trapping heat.

Record Dates (Selected from Copernicus/ECMWF data):
- 17 Sep 1979
- 30 Oct 1980
- 10 Oct 1981
- 02 Oct 1982
- 17 Oct 1983
- 25 Sep 1984
- 12 Oct 1985
- 06 Oct 1986
- 29 Sep 1987
- 20 Sep 1988
- 22 Sep 1989
- 03 Oct 1990
- 02 Oct 1991
- 19 Sep 1992
- 21 Sep 1993
- 25 Sep 1994
- 27 Sep 1995
- 07 Sep 1996
- 05 Oct 1997
- 20 Sep 1998
- 15 Sep 1999
- 06 Sep 2000
- 15 Sep 2001
- 18 Sep 2002
- 12 Sep 2003
- 17 Sep 2004
- 19 Sep 2005
- 15 Sep 2006
- 12 Sep 2007
- 13 Sep 2008
- 18 Sep 2009
- 25 Sep 2010
- 17 Sep 2011
- 22 Sep 2012
- 15 Sep 2013
- 01 Oct 2014
- 09 Oct 2015
- 19 Sep 2016
- 01 Oct 2017
- 20 Sep 2018
- 30 Sep 2019

CFC Abatement: Aggressively reduce the production and use of Chlorofluorocarbons (Verminder CFK’s).
Innovation: Find and utilize effective alternatives to CFCs (Vind alternatiewe).
International Support: Richer nations should provide financial and technical assistance to poorer nations to help them implement improved reductions of CFC emissions.