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Air Pollution Science Healthcare

What Exactly is Ozone? The Good, the Bad & the Ugly

Picture of Dr Gabriela Adler Katz
By Dr Gabriela Adler Katz on December, 7 2021

Our ozone layer serves as a lifesaving UV barrier for planet earth, functioning to absorb most of the sun’s ultraviolet radiation. At the same time, ground-level ozone pollution is extremely harmful to human health. As the complexity of ozone pollution is often misunderstood, let's take a closer look at this particular pollutant.

‘Good Ozone’: Our Essential Sun Shield 

The protective ozone layer which exists in the upper atmosphere is vital to life on earth. This ‘good’ ozone shields us from the sun’s harmful UV rays, which can cause skin cancer and destroy plants.

For many years now, environmentalists have urged the world to stop manufacturing harmful CFC (chlorofluorocarbons) chemicals that destroy our upper ozone layer, such as freon refrigerants used in air conditioners. The international community agreed on the Montreal Protocol in 1987 to provide strict guidelines to limit the use of ozone-depleting substances in order to restore the ozone layer.  

While the status of our atmospheric ozone layer has been improving over the last few years, a ‘hole’ still reappears annually between August to October in the Southern Hemisphere.

How is Ozone Created?

Ozone is a gas made up of three oxygen atoms (O3) and can be formed either in the upper atmosphere of our planet (the Ozone ‘shield’) or in the lower atmosphere at our human level - this is what we refer to as ‘ground level ozone’.

Scientists categorize ground-level ozone as a secondary pollutant, which means it isn’t emitted directly, but rather gets formed as a result of precursor pollutants released by cars, factories, power, or chemical plants in the presence of radiation from the sun.

‘Bad Ozone’: Ground-level Ozone & Impact on Health

Ozone exposure has a different impact depending on the population group and sensitivity factors. The most vulnerable individuals are children since their lungs are still developing. Next are those with weakened immunity and/or existing lung diseases as well as those who spend a lot of time outdoors. 

According to the EPA, people with reduced intake of certain nutrients such as Vitamins C and E may also be at greater risk from ozone exposure.




Depending on the level and duration of exposure, ozone pollution can inflame and damage the airways, trigger coughing, cause an irritated and sore throat, and make the lungs more prone to infection. These symptoms can show up in healthy people, but the short-term consequences can be far worse for those with lung diseases like asthma, sometimes causing school absence, visits to emergency rooms, and more. 

Long-term exposure to ozone has also been linked to asthma development and other chronic conditions. For example, a long-term study looking at the health of Canadian children found exposure to ozone at birth was associated with an 82% increased risk of developing asthma by age 3. 

When is Ozone Pollution Likely to be Highest?

As ozone requires the presence of solar radiation, levels are likely to be highest on dry, sunny days - if there’s little sun, ozone can’t form.

The Surprising ‘Weekend-Effect’

As man-made emissions contribute to ozone formation, you might assume ozone would also be lower on the weekends - when industrial activity and road traffic tend to slow down. However, ozone levels can actually increase during the weekend.



This is because the formation of ground-level ozone depends not only upon the concentration of specific elements - NOX , (Nitrogen Oxide), VOCs (Volatile Organic Compounds) and CO (Carbon Monoxide) - but also on the ratio of these different elements to each other, as well as the intensity of solar radiation.

As NOx is a primary pollutant emitted by vehicle emissions, when there are fewer cars on the road, there may be less NOx in the air. This might seem like a good thing for pollution in the city, but the impact on overall ratios means urban centers can actually experience higher levels of Ozone during quiet periods. This is what scientists dub the ‘Weekend Effect’ - it has also been witnessed during COVID-19 lockdowns. 

Ozone Pollution: What Can We Do About It? 

The complex reality of ozone formation underlines the importance of understanding the nature of individual pollutants. Different pollutants will peak and wane at different times, and It’s important for vulnerable individuals, in particular, to be aware of this.

Practical Steps for Businesses & Individuals

Measures for managing ozone exposure might include postponing a play in the park or switching a high-intensity exercise for an easier one until ozone levels reduce. It's also a good idea to close windows and activate purification systems on high ozone days.

BreezoMeter's Air Quality Technology

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