Why Ozone is Associated With Smog

Misconceptions about ozone unfairly give
this "good guy" a bad name.

What Is "Smog"?

Smog is chemical mixture of gases that commonly forms a brownish-yellow haze in the air, primarily over urban areas. Components of smog include ground-level ozone, nitrogen oxides (NOx), volatile organic compounds (VOC), sulfur dioxide, acidic aerosols and gases, and particulate matter. These gases result from a reaction between certain airborne pollutants and strong sunlight. Smog is most prevalent in the summer months, when there is the most sunlight and temperatures are the highest. Smog poses a significant threat to animal, plant, and human life in fact, thousands die every year as a result of this pollution. 

Smog Graph

Is Ozone Really the Culprit?

The so-called "ground level ozone" (called this to differentiate it from ozone in the upper atmosphere - the "ozone layer") that is said to be the "main culprit" in smog is really a collection hydrocarbons - CO CO, and SO  - that react with UV rays from the sun to form nitric oxides (NOX), halogenated by-products, and lead and sulfur compounds. These composites do indeed cause offensive odors, aggravate respiratory problems and burn eyes. But it is NOT the ozone that is the true villain. Ozone naturally forms not as a true component of smog but, more accurately, as a means of eliminating it. As the level of VOCs and particulate rises in the air, the ozone level rises as Nature herself tries to clean up man's mess!

If you remove the manmade components of smog - the VOCs and industrial particulates - then you simply have a natural process where the ozone and nitrogen dioxide are normalized to safe and healthy levels. When you add a large amount of man-made hydrocarbons to the equation, then the amounts of nitrogen dioxide and ozone are artificially increased.

The main reason that ozone gets the label of "Public Enemy Number One" is that while man-made hydrocarbons are very complex and as such quite difficult to measure, ozone is very easy to accurately measure. Consequently, ozone has long been used as an indicator for the severity or presence of smog because as the levels of the true components of smog rise, so does the level of ozone. 

By conveniently placing the onus on ozone, government and industry are effectively relieved of the responsibility for the millions of pounds of toxins released into the air every year. Rather than taking steps to control the real culprit, we are actually allowing our government to shoot the messenger - good guy ozone.

The Real Culprit

Ozone's beneficial role in smog reduction is its ability to break down and oxidize hydrocarbons and particulates in the air. One of the most powerful oxidants known, ozone actually burns (through a microscopic chemical reaction akin to an explosion) and destroys particulate with which it comes in contact. Ozone is unstable and highly reactive, and as such it readily seeks out molecules of particulate and gas with which to chemically react in an effort to break up the oxygen triplet - O3 - and return to its natural state: O2, or oxygen.

However, in the process of breaking down man-made hydrocarbons in particular, the result is the production of elements that combine to produce additional ozone and nitrogen dioxide, above and beyond what is produced naturally. Even though hydrocarbons are quickly being broken down by the ozone, the sheer volume of these pollutants that is produced by our highly-industrialized society is almost insurmountable. In our cities and industrial areas, where there is an extremely high level of hydrocarbons in the air, nature simply cannot keep up without overcompensating.

By itself, ozone is a natural purification agent used in a variety of ways for this purpose both by nature and by humans. At reasonable levels it is not at all unhealthy, and due to ozone's reactive and unstable nature it is very, very rare for ozone levels to become excessive under natural or normal circumstances. Conversely, man-made hydrocarbons are completely unhealthy at any level and under any circumstance. Common sense dictates that black, sooty smoke coming from an automobile exhaust or smokestack can only be harmful to your health.

Hydrocarbons do occur naturally in the air, as does the ozone that helps to break them down without reaching dangerous or unnatural concentrations. When excessive amounts of hydrocarbons are produced, largely man-made, you will get high ozone concentrations as a natural reaction to an unnatural situation. Rarely do less-populated areas experience smog and ozone problems, even though ozone is naturally produced the same way and in similar quantities in big and small cities alike. 

Ozone-Producing Air Purifiers - Choosing a Safe One

Modern, "air-tight" construction methods that began in the energy-conscious 1970s, combined with misinformation about ozone safety perpetuated by well-meaning public health agencies, has resulted in an unfortunate lack of ozone in most indoor environments. The reason this is so unfortunate is because in truth ozone is an effective, natural air purification agent which, when properly produced by a high-quality air cleaning system, can alleviate a wide range of health problems such as allergies, asthma, sinus problems, and chemical exposure.

The EPA has stated in no uncertain terms that indoor air pollution is the nation's number one environmental health problem - and it is a far more significant risk to human health than even the worst outdoor air pollution. Because it is the high hydrocarbon concentration that is a component of smog conditions that makes the ground ozone level artificially high, this is not a factor indoors. Even if you have many other kinds of pollutants in your home (and you do), hydrocarbons are the only contaminant will cause ozone levels to rise above safe levels. The scientific community is still not sure exactly why this happens; they only know that it does happen.

It should be clear that ozone is not the culprit of our pollution problems. Ozone has been used for half a century as a purifying agent for a variety of applications - water treatment and purification, food preservation, cancer and HIV treatment, and odor removal.

Most ozone air purifiers are designed to produce an ozone concentration of about .04 ppm (parts per million) when operated according to instructions, which is within all standards (including OSHA and the FDA). Fortunately, ozone is a self-policing element, since it's odor becomes obnoxious to most well before it becomes a health hazard, as opposed to the refreshing and purified smell it gives off when occurring at safe and healthy levels.


  • United States Environmental Protection Agency, Office of Air and Radiation, EPA Report 402-K-00-002, March 2000

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