What is Ozone?

Ozone is a pale blue gas with a sharp, pungent smell (you can often smell it after a heavy thunderstorm). Ozone is made up of three oxygen atoms and has the chemical formula O3.This differs from the Oxygen that we breathe, which is (somewhat confusingly) made up of 2 Oxygen atoms, O2. Even though both Ozone (O3) and the Oxygen we breathe (O2) are exclusively made up of Oxygen atoms, Ozone can be dangerous to human health.

Good vs Bad Ozone

On Earth, Ozone exists in two places: in and above the stratosphere, and on the ground. The stratosphere is a layer of the atmosphere between 6 and 30 miles above Earth’s surface (almost in space!), and here Ozone is called “Good” Ozone. Ozone found in and above the stratosphere forms a protective layer around the Earth, the Ozone Layer, shielding Earth’s surface from the harmful ultraviolet (UV) light emitted by the Sun. The Ozone Layer protects us from this UV radiation by absorbing it. “Bad” Ozone, on the other hand, exists in the atmospheric level closest to Earth, within six miles of the surface – where we live. This area is called the Troposphere. “Bad” Ozone can have a number of negative health effects. Ozone levels reported on HealthyEnviron are taken at ground level, and thus are a measure of this “Bad” Ozone.

Where does Ozone come from?

“Good” Ozone is naturally produced in the upper atmosphere when the sun’s UV light collides with a molecule of Oxygen in their air. Oxygen molecules are made up of two Oxygen atoms (that’s why it’s called O2), and the UV breaks these two Oxygen atoms apart. Oxygen atoms are not stable by themselves, and quickly collide with and bind to another O2 molecule in the air, forming O3: Ozone.

“Bad” Ozone, or the Ozone we’re exposed to on Earth’s surface, isn’t produced naturally, but rather exists as the result of human activities. The majority of Ozone that we’re exposed to is produced due to motor vehicle exhaust. Other major contributors are industrial and chemical processes, power plants, evaporating gasoline, and others. Ozone is typically produced in urban and suburban areas, or in areas industrial activity, but can be spread by the wind to other areas, including rural areas. Blown by the wind, Ozone can travel hundreds of miles.

Interestingly, human activities don’t typically emit Ozone directly, but rather human activities tend to emit intermediate compounds like volatile organic compounds (VOCs), other hydrocarbons, or most commonly, nitrogen oxides (NOx), which lead to Ozone production. For example, nitrogen oxides are unstable in the presence of sunlight: when an NOx molecule collides with a photon of UV light, it will kick off a single Oxygen atom. Just as in the upper atmosphere, this newly liberated Oxygen atom is unstable and will attack a nearby molecule of O2 in the air, producing Ozone O3.

The majority of “Bad” Ozone is produced due to motor vehicle exhaust. Other major contributors are industrial and chemical processes, power plants, evaporating gasoline, and others. Ozone is typically produced in urban and suburban areas, or in areas of industrial activity, but can be spread by the wind to other areas, including rural areas. Blown by the wind, Ozone can travel hundreds of miles.

What are the health effects of Ozone?

Fortunately, stratospheric Ozone is simply too high in the atmosphere for us to breathe in. Unfortunately, we are exposed to Ozone near the ground – in the Troposphere. Breathing in this “Bad” ground-level Ozone can cause chest pain, coughing and throat irritation and can worsen asthma, emphysema and bronchitis. Many scientists compare the effects Ozone has on the lungs to a bad sunburn: lung cells are damaged, and ultimately can die and peel away. Over time, exposure to Ozone can lead to scarring of the lungs, which results in permanently reduced lung function, making it more difficult to breathe for the rest of your life. Even worse, studies have linked Ozone exposure to tens of thousands of premature deaths each year.

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