Why Is Ozone In Our Air a Problem?

The EPA regulates substances in the environment that pose a threat to public health. Ozone is toxic because it is a powerful oxidizer (which means it can easily gain electrons from another substance). Click here to learn about why ozone is such a strong oxidizing agent. Ozone can react with cell-membrane lipids or proteins to form peroxide (also a strong oxidizer). These oxidizing agents can damage lung tissue.

Your body is capable of handling small doses of strong oxidizers like ozone. The surface of your lungs is covered with epithelial lining fluid. This thin layer of fluid over the epithelial surface of the respiratory tract has several antioxidants dissolved in it, including Vitamin C (ascorbic acid) and glutathione, shown in Figure 3. (Refer to the tutorial, Nutrients and Solubility, for more information on Vitamin C.) If the antioxidant solution covering the lung surface was not present, oxidizing agents (such as ozone) would react with the lung tissue itself, damaging the lungs.

Molecule Name and Formula

Two-Dimensional Representation

Three-Dimensional Representation

Ascorbic Acid

(Vitamin C)

2D Ascorbic Acid

3D Ascorbic Acid

Glutathione

2D Glutathione

3D Glutathione

Figure 3

This figure contains two- and three-dimensional representations of ascorbic acid and glutathione. Note that glutathione is a tripeptide, a molecule composed of three amino acids (in this case, glutamic acid, cysteine and glycine).

The 2D representations shown in this table were drawn using CS ChemDraw Pro. The coordinates for the 3D representations were obtained from molecular-modeling calculations using CS Chem3D Pro, and the images were rendered using SwissPDB Viewer and POV-Ray (see References).

Antioxidants react with oxidizing agents like peroxide and ozone to form harmless products, as shown in Equation 1 below. (Recall, various peroxides are formed in the lungs when O₃reacts with cell membranes. The simplest peroxide, hydrogen peroxide (H₂O₂), is used in the example below in Equation 1. Also note that dehydroxyascorbic acid is a nontoxic product.) Click here for more details on the oxidation-reduction reactions that protect your lungs.

Ascorbic acid + H₂O₂ ---> dehydroxyascorbic acid + 2H₂O

(anti-oxidant) (oxidizing agent) (harmless products)

(1)

When the concentrations of strong oxidizing agents are high enough, the antioxidants in the epithelial lining fluid can be used up faster than they can be replaced by the body. Like any other biological characteristic, the composition of the epithelial lining fluid varies from one person to another. Some people secrete smaller amounts of antioxidants into the protective fluid that covers the lung. This may help explain why some people are more sensitive to high levels of ozone (an oxidizing agent) in the air than others.

Because ozone is a strong oxidizing agent and could be a possible health threat, the EPA has regulated its presence in the atmosphere we breathe. Data show that the combustion of fossil fuels raises ozone concentrations. (That is why we are cautioned to limit driving on poor air-quality days.) But ozone itself is not a product of combustion, so how is ozone formed from the gases released by our automobiles?