The “Good” and the “Bad”
Ozone is an inorganic molecule with the chemical formula O3 or trioxygen. Right, it is very similar to O2 (dioxigene) and what we need to survive, but this additional oxygene atom makes it far less stable and makes it to a a very powerful oxidant. Ozone will oxides most metals (except gold, platinum and iridium) for example even at room temperature ozone will react with carbon C + 2 O3 -› CO2 + 2 O2. It is a pale blue with a distinctively pungent smell and many people can detect the sharp odor with a reminiscent of chlorine at concentrations as little as 100 ppb (parts per billion).
Right it is a gas, but even if it is a gas, we decided to give it an extra chapter and treat it separate from the rest of the gases.
- Firstly, we need to differentiate between two different kind of ozone. There is the “good” or “stratosphere” ozone what shields the earth from the sun’s harmful ultraviolet rays and there is the so called “bad” or “troposphere” (ground level) ozone which is an air pollutant that can seriously damage human health, vegetation and many common materials.
- Second Ozone is considered as a secondary pollutant as it is not emitted directly into the air (unlike the gases described in the tab hazardous gases) but is created by chemical reactions between oxides of nitrogen and volatile organic compounds (VOC) in the presence of sunlight. Sometimes referred to as photo-chemical smog.
Here we concentrate on the direct effects of air pollution on us humans and therefore we have a closer look on the troposphere ozone:
What causes ground level ozone
We learned above that “bad” ozone is created by a chemical reaction between oxides of nitrogen (NOx) and VOCs. Unfortunately, both components are produced by ourselves and are part of the general air pollution.
Sources of NOx: 56% Motor Vehicles, 22% Utilities and 17% Industrial/Residential fuel combustion
Sources of VOCs: 50% Industrial/Commercial Processes, 45% Motor Vehicles
You could say this is a problem for urban and suburban areas and you are right, the highest levels of ozone is measured there but many rural areas are also subject to high ozone levels, as winds carry emissions hundreds of miles away from their original sources.
That ozone can be created you need beside NOx and VOCs a third factor and that energy. As the most common form of energy is sunlight ozone levels are on their peak in the summer time. Even we said we will not talk about the “good” ozone one remark is important! The more energy the sunlight has the more “bad” ozone is produced and as ultra violet light carries the most energy it simply means that the more we destroy the stratosphere ozone the more ground level ozone we get. Beside sunlight ozone is also generated by any kind of electrical discharges (man-made discharges or lightening).
Health effects of ozone
If we breath in ozone it can trigger a variety of health problems including chest pain, coughing, and throat irritation. It can worsen bronchitis, emphysema, and asthma. Ozone also can reduce lung function and inflame the linings of the lungs also known as the sun burn of the lungs. Repeated exposure may permanently scar lung tissue. Even healthy people can experience difficulties in breathing when exposed to ozone pollution. Because ozone forms in hot weather, anyone who spends time outdoors in the summer may be affected, particularly children, older people, outdoor workers and people exercising.
The ozone does not only have just negative health effects, it cause also damages to materials, especially if it goes along with the presence of UV light or in combination with other air pollutants like sulfur dioxide and nitrogen dioxide. We are not talking only about oxidation of metals, but also of deterioration of Polymers (plastic) and rubber.
Ozone maximum exposure for humans is set to 120 µg/m3 (170 ppb) 8 hours