Ozone Pollution
Remember that truck exhaust? As you stare at that dark and gritty smoke, be aware that you can’t actually see all of its dangers. The dirty cloud of exhaust is a mass of particles, but hidden in the plume are the raw ingredients for the most widespread air pollutant: ozone, commonly known as smog. In major reviews published in 2005, we confirmed recent studies showing the deadly effects of this old public health nemesis.
What is Ozone?
Ozone (O3) is an extremely reactive gas molecule composed of three oxygen atoms. It is the primary ingredient of smog air pollution and is very harmful to breathe. Ozone essentially attacks lung tissue by reacting chemically with it. It also damages crops and trees. News about ozone can be confusing. Some days you hear that ozone levels are too high and other days that we need to prevent ozone depletion. Basically, the ozone layer found high in the upper atmosphere (the stratosphere) is beneficial because it shields us from much of the sun’s ultraviolet radiation. However, ozone air pollution at ground level where we can breathe it (in the troposphere) is anything but beneficial. It causes serious health problems.
Where Does Ozone Come From?
What you see coming out of the tailpipe on that truck isn’t ozone, but the raw ingredients for making ozone. Like some types of particle pollution, ozone is formed by chemical reactions in the atmosphere from those key raw ingredients that do come out of tailpipes, smokestacks and many other sources. These essential raw ingredients for ozone, nitrogen oxides (NOX) and hydrocarbons, also called volatile organic compounds (VOCs), are produced primarily when fossil fuels like gasoline or coal are burned or when fossil fuel-based chemicals, like paints, evaporate. When they come in contact with both heat and sunlight, these molecules combine and form ozone. NOX is emitted from power plants, motor vehicles and other sources of high-heat combustion. VOCs are emitted from motor vehicles, chemical plants, refineries, factories, gas stations, paint and other sources. The recipe for ozone is simple, and like any recipe, the ingredients must all be present and in the right proportions to make the final product.
NOX + VOC + Heat + Sunlight = Ozone
You may have wondered why “ozone action day” warnings are sometimes followed by recommendations to avoid activities such as mowing your lawn or refilling your gas tank during daylight hours. Lawn mower exhaust and evaporating gasoline vapors turn into ozone in the heat and sun. Take away the sunlight and ozone doesn’t form, so refilling your gas tank after dark is better on high ozone days. In the same way, if we reduce the chemical raw ingredients (NOX and VOCs) in the right proportions, ozone doesn’t form. Since we can’t control sunlight and heat, we must reduce the chemical raw ingredients if we want to reduce ozone.
