What is ground-level ozone?

Did you know that there are both “good” and “bad” types of ozone? Depending upon where it’s found in the atmosphere, ozone can either be beneficial for humans or dangerous to our health. Read on below to learn more about both types and how we can protect ourselves from the dangerous type of ozone.

A surfer walking across a polluted avenue lined with palm trees

Stratospheric ozone: the “good” type of ozone

The ozone layer is an important part of our atmosphere, laying between 25 to 30 kilometres above the Earth’s surface. Its purpose is to protect all living beings from the dangers of the sun’s ultraviolet rays.

Many of us are familiar with the hole that appeared in the ozone layer surrounding the Earth. This hole reached its maximum size in September 2000, the largest recorded since 1979, when it measured 28.4 million km2 (an equivalent of almost seven times the size of the European Union) in the Southern Hemisphere where ozone degradation is most dramatic. The hole was defined by ‘ozone column values measuring 220 Dobson Units (DU) or less’ (which, according to the European Environment Agency, is a unit used to determine ‘the total amount of ozone in a vertical column of air above the Earth’s surface’2) as represented by the blue colouration in the graph below1.

Progression of the hole in the ozone layer from 1979-2022

What was responsible for this hole that has put all of our health in jeopardy? You probably guessed it: human behaviour is to blame, particularly our use of ozone-depleting substances, or ODS. These substances consist of CFCs and HCFCs, carbon tetrachloride, halons, methyl bromide, and methyl chloroform which can be found in refrigerators, air conditioners, fire extinguishers, foam, aerosol propellants, and soil fumigants3. When released into the atmosphere, these materials remain stable in the troposphere but degrade significantly when exposed to ultraviolet light in the stratosphere. This degradation releases chlorine or bromine atoms which deplete ozone2.

The Montreal Protocol is an international treaty designed to protect the ozone layer from depletion and was first signed in 1987. At the time of its signing, it required all United Nations member states to achieve a 20% reduction in CFC use and emissions by 1994 and 50% by 1998 (compared to 1986 levels). There have been five amendments to the Protocol, and thanks to the swift action taken by member states (only 14 years passed between the discovery of the hole in the ozone layer and the passing of the Protocol), the ozone layer is expected to be fully healed by the middle of the 21st century4. The member states continue to meet annually to ensure its implementation.

Ground-level ozone: the ‘bad’ type of ozone

Ground-level ozone, a highly irritating and colourless gas, is not considered to be a ‘primary’ air pollutant but rather a ‘secondary’ air pollutant. This is due to the fact that it is not released directly into the atmosphere but, rather, is created by chemical reactions when oxides of nitrogen (NOx) and volatile organic compounds (VOCs), two types of air pollutants, combine in the air and create a chemical reaction as a result of exposure to sunlight5.

Whilst NOx and VOCs can have natural sources, their anthropogenic sources consist mostly of emissions from burning fossil fuels (petrol, diesel, natural gas, and wood) and coal in vehicles, industry, and domestic use6. Ozone is even used for purification of both air and drinking water7.

A graphic showing how ozone is produced (NOx + VOC + heat + sunlight)

5 Environmental Protection Agency: Ground-level Ozone Basics

Impacts of ozone

Ozone can pose a great deal of problems for people and the environment.

Effects on health

The degree of health impact depends upon several factors including duration and concentration of exposure. Symptoms vary from mild to severe depending upon these factors and may include:

  • Irritation of the eyes, nose, and throat
  • Coughing
  • Headaches
  • Reduced lung capacity
  • Shortness of breath and associated chest pain
  • Increased likelihood of contracting a respiratory illness, being hospitalised for respiratory illness symptoms, and/or experiencing an asthma attack for sensitive individuals
  • Increased risk of premature death8

The people most at risk of the negative effects of ozone include children (who tend to spend the most time outdoors during periods of peak pollution), people with asthma or other respiratory illnesses, elderly people, pregnant women, and people who are active or work outdoors9.

Effects on the environment

Ozone is toxic for plants. According to a study by the American Environmental Protection Agency (EPA), excessive ozone impacts sensitive plants’ abilities to produce and store minerals, making them more vulnerable to pollution, pests, disease, competition, and severe weather. It also reduces photosynthesis and slows a plant’s growth. Furthermore, ozone particularly impacts leaves of trees by reducing photosynthesis abilities, reduces crop yields, and hinders forest growth, reducing ecosystem biodiversity and changing habitat quality and water and nutrient cycles8.

The above effects have substantial economic consequences for both the agricultural and forestry sectors. A recent study estimates that on a global scale, ground ozone is responsible for crop loss of 3 to 16%, equating to economic losses of $14 to 26 billion USD (£11.2 billion or 12.7 billion €)10.

How can I reduce my ozone contributions and protect myself from its dangers?

The good news is that the best ways to reduce your ozone contributions are similar to those that help reduce all air pollutants! To keep our air cleaner, reduce your use of fossil fuels as much as possible. This means reducing the use of your car (try biking, walking, or using public transportation to get to your destination) or go electric. If you do need to take your car, never leave your engine idling, ensure that your tyres are properly inflated, and combine journeys and reduce trips. You can also favour the use of clean energies for heating your home by reducing your use of natural gas and wood and choose natural, low- or no-VOC products like paint and cleaning products for your home and office.

Refer to our article to read more about what you can do to reduce your contributions to air pollutants here.

An electric car charging at a charging station

Protect your health from the effects of ozone with Eoleaf

Eoleaf’s air purifiers are your best ally in clearing your air of pollutants, keeping them out of your lungs where they can wreak havoc on your health. Using our 8 filtration technologies (consisting of a pre-filter, natural bamboo fibre with a non-silver coating, a medical-grade HEPA H13 filter, an activated carbon filter, photocatalysis, UV sterilisation, and ionisation), our devices are designed to fight against different types of pollutants, removing all particles down to a size of 0.01 μm from your air. This means that all allergens (dust, pollen, pet dander), germs (viruses, bacteria), chemical pollution (VOCs), and fine particles (PM10, PM2.5, and PM0.1) are quickly and efficiently cleared from your space.

Not only is Eoleaf’s technology ozone-free (meaning that it does not release any ozone, but it actually filters ozone out of the air. Protect yourself and your loved ones from ozone today with Eoleaf.


1 Miletli, A. (2023, April 19). What is the current state of the ozone layer? European Environment Agency. Retrieved April 27, 2023, from https://www.eea.europa.eu/en/topics/in-depth/climate-change-mitigation-reducing-emissions/current-state-of-the-ozone-layer

2 Ozone-depleting substance. European Environment Agency. (2017, February 14). Retrieved April 27, 2023, from https://www.eea.europa.eu/help/glossary/eea-glossary/ozone-depleting-substance

3 Ozone depleting substances. Department of Climate Change, Energy, the Environment and Water. (2021, October 3). Retrieved April 27, 2023, from https://www.dcceew.gov.au/environment/protection/ozone/ozone-science/ozone-depleting-substances

4 Environmental Protection Agency. (2021, August 30). International Treaties and Cooperation about the Protection of the Stratospheric Ozone Layer. EPA. Retrieved April 27, 2023, from https://www.epa.gov/ozone-layer-protection/international-treaties-and-cooperation-about-protection-stratospheric-ozone

5 Environmental Protection Agency. (2022, June 14). Ground-level Ozone Basics. EPA. Retrieved April 27, 2023, from https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics 

6 Government of Canada / Gouvernement du Canada. (2016, May 19). Common air pollutants: ground-level ozone. Canada.ca. Retrieved April 27, 2023, from https://www.canada.ca/en/environment-climate-change/services/air-pollution/pollutants/common-contaminants/ground-level-ozone.html

7 Centers for Disease Control and Prevention. (2019, June 22). Ozone. National Institute for Occupational Safety and Health. Retrieved April 27, 2023, from https://www.cdc.gov/niosh/topics/ozone/default.html

8 Ozone harmful to humans, plants and vegetation. Ontario newsroom. (2008, July 29). Retrieved April 27, 2023, from https://news.ontario.ca/en/backgrounder/2056/ozone-harmful-to-humans-plants-and-vegetation

9 Environmental Protection Agency. (2022, June 14). Health Effects of Ozone Pollution . EPA. Retrieved April 27, 2023, from https://www.epa.gov/ground-level-ozone-pollution/health-effects-ozone-pollution

10 Emberson, L. (2020). Effects of ozone on agriculture, forests and Grasslands. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 378(2183), 20190327. https://royalsocietypublishing.org/doi/10.1098/rsta.2019.0327

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