Ozone Levels Were First Measured in the Early 1970S. in 1991, There Was Found a Decrease

Ozone Background Ozone levels were first measured in the early 1970s. In 1991, there was found a decrease in Antarctic ozone of about 60% compared to prior dates. No change in ozone levels was detected in the tropics. Studies in the Swiss Alps indicate levels of UV radiation have increased during the last decade. The increase may be due to thinning of the ozone layer. Ozone is the only atmospheric gas that effectively absorbs UV radiation.

In addition to other problems resulting from ozone loss, it is suspected that North America’s coral reefs have been bleached. Florida botanist Jerry McClure says UV radiation causes decreased crop yields in soybeans and barley. He suspects other crops are affected as well.

Causes of ozone depletion are mentioned in the student activity. Other contributing factors include the emission of nitrogen oxides and water vapor from supersonic aircraft in the lower stratosphere.

Three reasons suggested for the greater effects on the ozone layer over Antarctica and the Southern Ocean are:

1. Antarctica has the coldest air on the Earth, a circumstance that causes clouds to form at much higher altitudes. The higher clouds located in the stratosphere (called noctilucent clouds), where the ozone layer is found, are composed of ice crystals made of nitric acid and water. The ice crystals enable the chlorine from CFC’s to destroy ozone molecules more effectively than air lacking ice crystals.

2. Strong winds above Antarctica from a circular pattern that resembles a vortex. This air contains a mixture of chlorine, bromide, ozone, and ice crystals – all of which are held tightly in place until warmed by the spring sun.

3. By September, the end of the southern winter, the long Antarctic night has produced the coldest temperatures, the highest clouds, and the strongest winds – the circumpolar jet. The rising sun triggers a chain reaction of ozone destruction. That is when the hole appears. As the air is gradually heated by the rising sun, the southern hemisphere’s air is diluted by ozone-poor air flowing out the ozone hole location.

In addition, there is evidence for a smaller decrease in ozone at middle and northern latitudes, especially during the winter and early spring. Scientists do not yet completely understand the mechanism that would explain this phenomenon.

The term ozone “hole” is somewhat of a misconception. Ozone levels refer to the concentration in any given location. Therefore, when one talks about an ozone “hole”, he/she is referring to an area of greatly reduced levels of ozone measured in Dobson Units. Concentrations less than 200 DU are considered serious. These areas of reduced ozone move and fragment into multiple cells and recombine continually. NOx, VOC’s, and Groundlevel Ozone

(Boilers, Auto Engines)

N2 (g) + O2 (g) High Temps 2NO 79% of 20% of (Nitric Oxide) Tropospheric gases Tropospheric gases

2NO + O2 2NO2 (Nitrogen Dioxide) The NO2 is Brownish and gives photochemical smog its characteristic color.

NO2 + Warm/Sunny Air NO + O + O3 + O2 NO2 + O2 O3 Ozone reacts with nitric oxide almost as fast as it forms.

How VOC’s keep NOx from breaking down ozone:

NO + VOC’s NO2 + O3 (Mostly Hydrocarbons)

Therefore, not as much NO exist to remove O3, so tropospheric Ozone levels increase.

Both NO2 and O3 are photochemical oxidants; they can react with and oxidize certain compounds, e.g., car tires/ other rubber products, plastics, plant tissue, lung tissue, eye tissue.

In addition, both O3 , and free O atoms react with VOC’s to produce aldehydes (e.g., formaldehyde, acetaldehyde, acrolein)