Ozone – Friend or Foe?

Ozone has been a popular term for many years. We hear about the ozone layer, how it is thinning, and how important it is to protect both it and ourselves. We hear about the "ozone hole" and how it has been severely depleted. Although the depletion has recently been halted thanks to new regulations, its recovery will take at least another 50 years. We also hear about ozonization and its benefits in the environment around us and in industrial applications.

However, nowadays, especially during the summer months with rising temperatures, we hear about ozone alerts in the weather. Poor air quality triggers warning signals, and ozone emissions need to be reduced, as they can be harmful to our health.

So, how can ozone be both good and bad, a friend and an enemy?
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Oxygen makes up about 21% of our atmosphere. A single oxygen atom is unstable – it wants to bond with something else. Therefore, oxygen almost always exists in pairs as O2. However, under certain conditions, a three-atom molecule with the chemical formula O3 can form: Ozone. It is a pale blue gas with a distinctly sharp odor. Most people can detect its presence in the air at concentrations of around 0.02 ppm (40 μg/m³) or lower. It has a very specific sharp smell, somewhat resembling chlorine bleach. The total mass of ozone in the atmosphere is about 3 billion metric tons. This may seem like a lot, but it only makes up 0.00006 percent of the atmosphere.

Ozone is a highly reactive gas, and although it is unstable at high concentrations, it can bring valuable benefits. Its half-life depends on conditions such as temperature, humidity, and air movement.

What determines whether ozone is a friend or an enemy? The location.

Ozone is both a natural and man-made product. It exists in the upper layers of Earth's atmosphere (the stratosphere) and in the lower layers (the troposphere). Depending on where it is located in the atmosphere, it can have either a positive or negative effect on life on Earth.

Ozone in the stratosphere (our friend)

Ninety percent of the ozone on Earth is located in the stratosphere. This is the second layer of the Earth's atmosphere, situated between 10 and 50 kilometers above the Earth's surface. It is partially responsible for the deep blue beauty of the sky at dusk.

Ozone in the stratosphere forms naturally through a two-step reactive process. Ultraviolet (UV) sunlight interacts with molecular oxygen (O₂). In the first stage, sunlight breaks apart the oxygen molecule, creating two separate oxygen atoms. In the second stage, each atom collides and bonds with another oxygen molecule, forming an ozone molecule (O₃). These reactions occur continuously. As a result, the highest ozone production occurs in the tropical stratosphere. Chemical reactions with reactive gases, such as hydrogen, nitrogen oxides, and also chlorine and bromine, maintain the natural balance of ozone levels.

Ozone layer

Similar to a sponge, the ozone layer in the stratosphere absorbs about 98% of the harmful ultraviolet radiation coming from the Sun, thereby protecting the Earth's surface. It shields the most energetic UV-C radiation, most of the UV-B radiation, and about half of the UV-A radiation. UV-B and UV-C are so energetic that they can destroy life on Earth. Exposure to UV-B or UV-C radiation can result in sunburns. UV-B radiation also increases the risk of developing cancer and has many other health consequences. At this altitude, ozone is essential for life on Earth.

Ozone Hole

Despite the fact that ozone in the stratosphere is continuously produced and removed through natural processes, industrial pollution "created by humans" causes "new leaks into the bucket," thereby reducing ozone levels in the stratosphere. Ozone-depleting substances contain various combinations of chemical elements: chlorine, fluorine, bromine, carbon, and hydrogen, and are often collectively referred to as halocarbons. Compounds containing only chlorine, fluorine, and carbon are called chlorofluorocarbons (CFCs). CFCs, carbon tetrachloride, and methyl chloroform are important ozone-depleting gases produced by humans and are used in various applications, including refrigeration, air conditioning, foam production, cleaning electronic components, and as solvents.

Although CFCs are inert in the troposphere, they can be slowly transported to the stratosphere. There, they break down into molecules like chlorine monoxide (ClO), which depletes ozone by converting it back into oxygen. Another important group of human-made halocarbons are halons, which contain carbon, bromine, fluorine, and (in some cases) chlorine, and are primarily used as fire extinguishing agents.

What happens when the ozone layer degrades, causing it to become significantly thinner in certain areas, is unfortunately all too well known and scientifically documented, as the ozone hole over Antarctica has formed. The term is somewhat misleading, as the ozone layer doesn't actually have a true hole, but rather has become much thinner and depleted.

The image above: view of the South Pole from the NASA TOMS (Total Ozone Mapping Spectrometer) satellite. Blue and green indicate relatively high amounts of ozone. Red and yellow markings represent the "ozone hole," an area where ozone depletion has occurred. Credit: NASA

The bans on the use of various chemicals, especially the CFC group, have led to the gradual regeneration of the ozone layer, with an emphasis on slow restoration. Current projections suggest that it will take more than fifty years before conditions similar to those of the mid-20th century can be reached again.

The reduced ozone levels have led to an increase in the amount of harmful ultraviolet radiation reaching the Earth's surface. When scientists refer to the ozone hole, they mean the destruction of the stratospheric "good" ozone.

So, if this is good, where do we find what is bad?

Ozone in the troposphere (our enemy)

At the Earth's surface, ozone comes into direct contact with life forms and displays its destructive side (hence it is often called "bad ozone"). Due to its strong reactivity with other molecules, high levels of ozone are toxic to living systems.

In the lower layers of the atmosphere near the Earth's surface (the troposphere), ozone is produced through chemical reactions involving naturally occurring gases and pollutants, primarily as a result of photochemical reactions between two main classes of air pollutants: volatile organic compounds (VOCs) and nitrogen oxides (NOx). These reactions are partly dependent on the presence of heat and sunlight, which results in higher ozone concentrations in the environment during the summer months, often experienced as "smog" or haze. This can be extremely hazardous to our health and can cause a range of physical ailments, significantly affecting productivity. This is when ozone alerts are triggered.

Health risk assessment

Ozone toxicity occurs on a continuum, where higher concentrations, longer exposure times, and increased physical activity during exposure lead to greater effects. Short-term acute effects include respiratory symptoms, changes in lung function, increased airway reactivity, and inflammation of the airways. Exposure to ozone has been associated with an increased number of hospital admissions due to respiratory causes and asthma exacerbations.

Ozone and How We Use It to Our Advantage

Although ozone is toxic, it is used in various ways to our benefit. Perhaps less known, it is one of the strongest and most environmentally friendly oxidizers, making it one of the most powerful disinfectants in the world, second only to fluorine. It is three thousand times stronger than chlorine. For the past 100 years, ozone has been commercially used to reduce unpleasant odors (think of ozone treatment in cars to get rid of unwanted smells) and to purify water (drinking water treatment for sterilization). This substance is a highly effective antibacterial, bactericidal, and antifungal agent, breaking down organic material into its basic compounds. Its high oxidative potential makes ozone very useful and widely applicable for cleaning clothes, as well as for cleaning and killing mold and bacteria in air streams.

Everything in moderation.

Ozone, like many other things, can be very useful and valuable for human health, depending on its location and concentration. At low concentrations, it is present everywhere in our environment. It forms naturally, even in the troposphere, for example near rapidly moving water, such as waterfalls, or during storms created by lightning discharges. It is no coincidence that the air near a waterfall or after a storm is perceived as fresher because ozone has the mentioned strong cleansing effect and is capable of breaking down pollutants (odors) and microorganisms.

Jednak ozon pozostaje gazem toksycznym o właściwościach chemicznych i toksykologicznych znacznie różniących się od tlenu. Z tego powodu ustanowiono normy zdrowotne i zalecenia dotyczące ograniczenia narażenia ludzi, aby pomóc wyznaczyć granicę między korzystnym detergentem a działaniem drażniącym na zdrowie.

How much ozone is too much?

The EU currently defines the following reference levels for ozone concentrations: - At 0.09 ppm (180 μg/m³), the public should be informed. Sensitive individuals should avoid physical exertion in this environment starting from this concentration. - The alert threshold is set at 0.12 ppm (240 μg/m³). At this level, all individuals should avoid physical activity in this environment. - For prolonged exposure in enclosed spaces, such as workplaces, the EU currently sets the reference level at 0.06 ppm (120 μg/m³). Concentrations below this level are considered safe for human health.

Since the human sense of smell can detect ozone even at much lower concentrations—depending on sensitivity, as low as 0.02 ppm (40 μg/m³) or less—people have a natural warning mechanism.

What is your local air quality index today? Learn here

Bi-polar Ionization and Ozone

Before a storm, there is a very high concentration of pollutants in the air, such as bacteria, allergens, and VOCs. A thunderstorm releases high-voltage electrical discharges, emitting high concentrations of positively and negatively charged ions. The lightning also generates ozone through the electrical excitation of oxygen molecules. The ions produced in this process play a key role in reducing pollution and are crucial in providing us with fresh and clean air in nature.

This air purification principle achieved through bipolar ionization is comparable to this natural phenomenon. Our devices treat the air as if it were under the influence of a cleansing storm. The charged ions and a small amount of ozone create "activated oxygen"—which binds pollutants in the space where you breathe, just as nature does. Activated oxygen initiates an oxidation process that chemically changes the molecules of odors and germs. New harmless substances are formed. Activated oxygen damages the cell structure of mold spores and bacteria, rendering them inactive. The activated air acts as a natural cleaner in the room, restoring and rebalancing the air in enclosed spaces.

In the process of bipolar ionization, ozone is generated, but we are talking about concentrations in the range of 0.01 ppm. For comparison, the current EU Directive sets a value of 0.06 ppm (120 μg / m³) for longer exposure, such as 8 hours a day, 5 days a week. In this case, there is no threat to human health. Additionally, we offer sensor-based control in our ionization systems, where ozone sensors are used for protection to avoid any risks or evolving threats.

In nature, humans are always exposed to some low concentrations of ozone, which, unless they lead to increased accumulation, do not affect their health.

In conclusion, friend or foe is always subjective in terms of quantity and location. Know your facts before making a judgment.