Air Quality in Arizona: Ozone

I will continue the discussion on air quality in Arizona, particularly as it affects patients with allergies and asthma, beginning with one of our most important pollutants: ozone.

diagram-29982_1280 (1)Ozone in the upper atmosphere is our friend.   This thin layer of gas floating between 6 and 31 miles above the earth’s surface protects life on our planet by filtering harmful ultra violet rays from the sun.

Ground level ozone is another story.  This insidious byproduct of automobile exhaust can damage living tissue just as it’s relative in the upper atmosphere protects it. Even the chemical structure of ozone looks like it would be friendly enough: it is just like oxygen, O2, with one more oxygen atom added to make O3 -a super oxygen!

But as vital as oxygen is to sustain human life, too much can be deadly.  To understand why, think about the effect of oxygen on a forest fire on a windy day or what happens to an unpainted iron fence -even in Arizona where it rarely rains.

Rusty BoatWhen wood burns or iron rusts, oxygen is at work in a process called oxidation. Oxidation can turn a battle ship into a heap of rust and kill all the bacteria and algae in your swimming pool.

In fact our immune system uses the deadly effects of oxidation to fight off disease.  Our white blood cells release powerful oxidizing chemicals like hydrogen peroxide and what are called, “reactive oxygen species,” or ROS, that kill and even digest invading pathogens.  This is great when you need to get rid of an infection, but we don’t want these chemicals loose in our bodies digesting us.090114_2215

To keep our white blood cells from eating holes in our lungs and liver, anti-oxidants are produced that are capable of neutralizing the oxidizers and preventing damage. Important antioxidants include vitamin A, vitamin E, beta-carotene, vitamin C, and glutathione as well as many other compounds found in food, especially vegetables and fruits.

When chronic inflammation occurs as a result of injury, infection, allergies, or immunologic processes, excessive amounts of these oxidizing chemicals are produced creating a condition called “oxidative stress”.  This stress can contribute to the pathogenesis of a wide variety of disease states including heart failure, atherosclerosis, and cancer as well as to the normal process of aging.

The role of diet and vitamin supplementation in the treatment and prevention of chronic disease is an important subject and one that I will review in more detail in a later post.   For now, the point I would like to make is that oxidative exposure from external sources can overwhelm our anti-oxidant resources and can contribute to the development and exacerbation of chronic disease.

Which brings us back to ozone.

Ozone is a killer oxidizing agent – powerful enough to be used commercially to sterilize water supplies. It is definitely not something you want to spend much time inhaling.  Exposure above as little as 100 ppb (parts per billion) can be harmful, causing symptoms such as nose, eye, and throat irritation, coughing, wheezing, shortness of breath, painful breathing, nausea and headache, and has been linked to increased incidence of asthma, bronchitis and heart disease.  Long-term exposure has been linked to increased risk of death from lung disease.

Untitled design (36) (1)According to the Maricopa Air Quality Department, ozone levels in our area are can reach unhealthy levels on “hot, sunny days when there is little wind”, which pretty much describes most days in Phoenix from May until October. For example, about a week out of the month of July, 2013 were under a high pollution advisory and health watch for ozone. This year the American Lung Association ranked Phoenix as the 11th most polluted city in the US for ozone.

In recognition of the adverse health effects of ozone, air quality guidelines have been established by the World Health Organization, European Union, and the US Environmental Protection Agency (EPA).   In 2010, the EPA announced proposed revisions to the National Ambient Air Quality Standard (NAAQS) for ozone with the following statement:

EPA proposes that the level of the 8-hour primary standard, which was set at 0.075 μmol/mol in the 2008 final rule, should instead be set at a lower level within the range of 0.060 to 0.070 μmol/mol, to provide increased protection for children and other ‘‘at risk’’ populations against an array of ozone – related adverse health effects that range from decreased lung function and increased respiratory symptoms to serious indicators of respiratory morbidity including emergency department visits and hospital admissions for respiratory causes, and possibly cardiovascular-related morbidity as well as total non- accidental and cardiopulmonary mortality…

In addition, the Air Quality Index (AQI) was developed by the EPA to explain air pollution levels to the public. Using this scale, eight-hour average ozone levels of 85 to 104 nmol/mol are considered “unhealthy for sensitive groups,” 105 nmol/mol to 124 nmol/mol as “unhealthy,” and 125 nmol/mol to 404 nmol/mol as “very unhealthy.. The current AQI for Maricopa county and surrounding areas can be found at

Ozone exposure can have a significant negative impact on lung function, particularly in athletes involved in outdoor sports, a topic I will explore further in the next post.

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