Ozone (O 3 ) Ozone is a form of oxygen. The molecule contains three - - PowerPoint PPT Presentation
Outline Ozone: Earths shield from UV radiation Review electromagnetic radiation absorptivity by selective gases temperature vs. height in atmosphere Ozone production and destruction natural balance anthropogenic influence
Outline
electromagnetic radiation absorptivity by selective gases temperature vs. height in atmosphere
natural balance anthropogenic influence
electromagnetic radiation
contains three oxygen atoms (O3)
combine with other atoms.
it blocks the sun's ultraviolet (UV) waves and prevents them from reaching the earth's surface.
where it can damage living tissue and human-produced objects. It is generated both from certain types of pollution and natural sources.
1. Stratospheric ozone is a UV-shield:
and composition of troposphere. – This is not a theory to be tested - it is reality! – O3 hole, trends in O3 abundance, etc.: need predictions.
composition.)
stratospheric O3 and CFCs simultaneously?
2
To understand how ozone is generated and the functions it serves in Earth's atmosphere, it is important to know something about the electromagnetic spectrum — the energy emitted from the sun. Electromagnetic energy is sometimes described as traveling in waves and sometimes as traveling in packets of energy referred to as photons. Progressing from short wavelengths to long wavelengths, scientists have identified gamma rays, x-rays, ultraviolet radiation, visible light (between 400 and 700 nanometers), infrared radiation (heat), microwaves, and radio waves. Short wavelengths have more energy per photon than long wavelengths
Energy from the sun reaches the earth as visible, infrared, and ultraviolet rays
Only UVA and UVB ultraviolet rays reach the earth's surface. Earth's atmosphere absorbs UVC wavelengths.
temperature vs. height
in the troposphere temperature decreases with height the average lapse rate is about 5-9 degrees C per kilometer depending on the humidity in the stratosphere temperature increases with height in the stratosphere ozone absorbs incoming ultraviolet radiation 80% of the mass of Earth’s atmosphere is in the troposphere, we all live in the troposphere
Ozone
In the stratosphere, we find the "good” ozone that protects life on earth from the harmful effects of the sun's ultraviolet rays. In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog.
Ozone is also destroyed by the following reaction:
Although the UV radiation splits the ozone molecule,
in no net loss of ozone:
Because of their chemical stability, low toxicity, and valuable physical properties, these chemicals, versatile and stable in the lower atmosphere, at least, have been extensively used since the 1960s as refrigerants, industrial cleaning solvents, propellants in aerosol spray cans, and to make Styrofoam.
– Aerosol propellant – Refrigerant (refrigeration, building and mobile air conditioning) – Blowing agent for flexible and rigid plastic foams
The more recent trend for CFC11 and CFC12: mixing ratios in ppt Source: NOAA/CMDL
transports (SST)
– US cancelled SST, largely for economic reasons – UK/France built Concorde
– Ozone discussed, but mostly about noise, technology
published
– Attracted little attention
discussed work at American Chemical Society
– Widely publicized (e.g., two New York Times articles)
Discovery of Threat to Ozone
"for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone”
Paul J. Crutzen Mario J. Molina
The following animation shows the destruction of an ozone molecule by a chlorine atom.
1. UV radiation breaks off a chlorine atom from a CFC molecule. 2. The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the
3. The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO). 4. The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary
5. The chlorine atom is now free to attack and destroy another ozone molecule (O3). One chlorine atom can repeat this destructive cycle thousands of times.
1. Ozone is a naturally occurring gas found in the troposphere and other parts of the atmosphere. 2. Tropospheric ozone is often called "bad" ozone because it can damage living tissue and break down certain materials. 3. Concentrations of ozone are not uniform in the troposphere. 4. Longer exposure to ozone will increase the negative effects. 5. The amount of ozone present in the troposphere varies from day to day and from place to place. place to place
– Secondary pollutant formed through photochemical reactions involving NOx and VOCs in the presence of bright sunshine with high temperatures
– Increased hospital admissions for pneumonia, chronic obstructive pulmonary disease, asthma, allergic rhinitis, other respiratory diseases – Increased mortality
characteristics are the primary determinants of ozone exposure
trend is expected to continue over the next 50 years
– Emissions depend on assumptions of population growth, economic development, and energy use – Fraction attributable to climate change is the portion that is the consequence of climate change on local temperature & UV – Assuming no change in the concentration of precursor emissions, the frequency of future ozone episodes will depend on the occurrence of the requisite meteorological conditions
uv index
The UV Index provides a daily forecast of the expected risk of overexposure to the sun. The Index predicts UV intensity levels on a scale of 0 to 10+, where 0 indicates a minimal risk of overexposure and 10+ means a very high risk