Most of the oxygen atoms in the atmosphere are in the form of “Molecular Oxygen” that consists of 2 oxygen atoms. Ozone is a molecule of 3 oxygen atoms. Both types of oxygen molecules will react with other chemicals or elements. Molecular oxygen is used by the cells of our bodies to produce energy by reacting with sugars, fats and other energy storage molecules. Molecular oxygen will react with iron and cause iron to rust (iron oxide). Ozone is much more reactive than molecular oxygen. Ozone can oxidize cell membranes and many biological molecules. At high concentrations, ozone can damage cells and tissues faster than they can be repaired.
At ground level, some ozone is produced naturally when sunlight hits the atmosphere. Low levels of ozone naturally occur in the air we breathe and humans tolerate ozone at low levels. However, certain types of air pollutants can increase ozone to levels that are unhealthy to breathe. The US EPA considers a concentration of ozone at ground level above 0.070 parts per million (ppm) to be unhealthy. When ozone levels rise, some industrial production that promotes ozone may be suspended. Too much ozone at ground level is a bad for health.
In the upper level of the atmosphere (the stratosphere) ozone has a protective role. Ozone in the stratosphere restricts the amount of UV radiation that strikes the Earth’s surface and protects life on earth from damaging UV radiation. In the history of life on earth, all life was confined to the oceans until photosynthetic organisms released sufficient oxygen to create an ozone layer. Without the ozone layer, life on land as we know it could not exist.
The Earth’s protective ozone layer is under attack from man-made chemicals. These “ozone depleters” include the chlorofluorocarbons that were (in the recent past) commonly used in air conditioning and as propellents in aerosols. Ozone depleters have reduced the overall amount of protective ozone and create an “ozone hole”, a severe depletion of ozone that allows too much harmful UV radiation to reach the earth’s surface. The ozone hole is most severe of the Arctic and Antarctic in their respective Springs after the colder temperatures of Winter and interactions with high clouds make the ozone depleters more potent.
The effect of ozone depletion and the ozone hole on insects is mixed. Some plants (and insects) are more sensitive to UV radiation than others and this leads to changes in the environment. Some insect will benefit, others will decline or even go extinct. As in most situations, environmental change benefits some but harms others.
To stop the ozone destruction, countries around the world agreed (Montreal Protocol) to limit the use of ozone depleters, primarily by substituting less harmful chemicals for the ones currently in use and phasing out the bad chemicals. The phaseout was supposed to be complete by 2004. However, some of the chemicals and their uses have been extended by some countries.
Methyl Bromide is an ozone depleter that was, by treaty, to be banned by 2004. European Countries followed through with the agreement to halt use of methyl bromide. The US, one of the largest users of methlyl bromide, has not followed through on the treaty obligations and continues methyl bromide use to this day.
A primary use for methyl bromide is fumigation of food in storage to kill insect pests and eliminate infestations. The grain storage or food storage warehouse is filled with methyl bromide for a short period of time (typically 24 h or less). After the fumigation, the methly bromide is released into the atmosphere where it eventually reaches the stratosphere and acts as an ozone depleter. The methyl bromide fumigant is popular because it leaves little residue behind and is not corrosive to the structure.
European countries use alternative products for fumigation. One alternate product is ozone. The storage area is filled with high concentrations of ozone (50 ppm or higher). Obviously, this is above the level of ozone that is safe for humans (and insects). After treatment, the ozone is vented and rapidly diluted. On release, ozone treatments do not increase local atmospheric concentrations of ozone because the total amount of ozone is very small compared to the atmosphere outside. Unfortunately, ozone used for fumigation does not help with the ozone depletion occurring in the stratosphere.In the US, ozone treatments must compete with methyl bromide. Companies must invest in a different type of equipment to use ozone and the initial investment stands in the way of replacing methyl bromide with ozone. Following through with the methyl bromide ban would initially increase the costs of fumigation, but once the investment in new equipment was made, costs would be comparable to methyl bromide. Meanwhile, much of the ozone technology is being developed in Europe and the US is missing out on an investment opportunity by clinging to methyl bromide.