If you have been coughing and sneezing a lot lately, if your eyes are stinging and the inside of your mouth feels like it is on fire, the cause is likely to be ozone. The Pima County Department of Environmental Quality has issued an advisory for moderately elevated levels of surface ozone, currently at about 45 parts per billion, where up to 37 ppb is considered ‘good’.

Ozone is produced when a third oxygen atom attaches itself to a regular 2-atom oxygen molecule.  When oxygen compounds are stressed by high heat, they break up into their component atoms. Oxygen atoms like to be in pairs and so these disenfranchised oxygen atoms go looking for a mate. If they find another single, everything is fine, but chances are that they encounter a normal oxygen pair  and in desperation attach to the happy couple like cousin Freddy from Minnesota. Of course, he soon wears out his welcome and gets kicked out at the first opportunity. This restores the connubial harmony in the oxygen molecule, but it makes cousin Freddy so mad that he will attack anything in his path until he finds a new mate.

Cousin Freddy’s agression can be put to good use, for instance by directing him to kill the bacteria in drinking water or on food products, which he does much more cleanly than chlorine does. But when he is roaming about freely in the open air, he will indiscriminately attack anything organic, whether it be mucous membranes, plants cells or the rubber hoses in car engines.

The two ingredients required for the creation of these maverick oxygen atoms are smog and lots of heat. The heat is provided by the sun, by lightning and by high-voltage appliances such as photocopiers and tasers. The smog is provided by fossil-fuel combustion engines. More smog, more heat, more Freddies.

So, by and large, when ozone is near the ground, it stinks, which is what ‘ozone’ means in Greek. But when it is high up in the atmosphere, it is crucial to life on earth, because there it absorbs most of the deadly ultra-violet radiation from the sun. However, the ozone cover in the upper atmosphere has declined over the past 40 years because ozone also binds readily to compounds consisting of chlorine, carbon and fluorine atoms, known as CFCs or by the brand name Freon and used in refrigerants and as driving gas in spray cans.

The reactivity of ozone with CFCs is proportional to temperature and so the biggest depletion is over Antarctica, where the light of the sun is reflected back by the ice. This is known as the ‘ozone hole‘. When the ozone hole was discovered in 1979, it received wide attention in the media, but you don’t hear much about it anymore, because the story is boring: it just keeps on growing. In 1979 it was at about 380 square miles; in 2015, it was almost 10,000 square miles.  However, the actual quantities of ozone over Antarctica have gradually increased since the phase-out of CFCs started under the 1989 Montreal Protocol.

So there is good ozone and there is bad ozone. You can reduce formation of bad ozone if you:

• Drive less by combining trips, taking the bus, biking, walking or carpooling;
• Avoid idling your vehicle’s engine. Stay out of drive-thru lines – park and go inside;
• Re-fuel your car after dark when fumes are less likely to form ozone;
• Do no top off when refueling;
• Make sure the gas cap is on tight;
• Check your tire pressure monthly to reduce fuel consumption;
• Avoid using gas-powered lawn and gardening equipment;
• Conserve electricity to reduce emissions from power plants.

(Broadcast 3:48)

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