Updates from Environmental Experts

Understanding Good Ozone vs. Bad Ozone


Ozone can be a lifesaving UV barrier  for the world or responsible for harmful Ozone air pollution with devastating health impact. As its complexity is often misunderstood, let’s look at the facts together.

The Catch with Ozone

Ozone is a gas produced in two ways:  It can be formed naturally in the upper atmosphere of our planet (from oxygen), where it protects us from most of the sun’s harmful ultraviolet radiation (UV) rays. However, Ozone can also be produced in the lower atmosphere (at street level) partly as a result of human activities and this form is toxic for our health.

About 'Good' Ozone

The protective ozone layer present in the upper atmosphere is vital to life on earth. It is the good ozone that helps shield us from the sun’s harmful UV rays, which can cause skin cancer and destroy plants. The fact is, without the “good” ozone, there wouldn’t be any life on our planet that could survive. This is the reason why environmentalists urged the world for many years to stop manufacturing harmful chemicals that destroy upper ozone, such as freon refrigerants used in air conditioners. The international community agreed on the Montreal Protocol in 1987 to provide strict guidelines to conserve and restore the ozone layer.

About 'Bad' Ozone

Smog is a distinctive and easily recognizable form of urban air pollution. What most of us don’t know is that what is usually referred as smog is “bad” ozone.
Scientists categorize ozone as a secondary pollutant: it is formed by the combination of precursor pollutants - emanating from cars, factories, power or chemical plants - with volatile organic compounds, and the light from the sun. While we, humans, are entirely responsible for creating street-level or lower atmosphere ozone, the gas is extremely dangerous to our health.

For the science lovers, here are the two equations creating the ground level ozone pollutant:

R + 2NO + 2O2 → RO + 2NO2 + H2O

NO2 + hv + O2 → NO + O3

Health Implications of Ozone Pollution

Ozone can do a lot to your health, and is especially harmful to your respiratory system. It can create or worsen respiratory diseases, damage your lungs, and ultimately cause death.

Ozone will have a different impact depending on population groups: the most vulnerable are children (since their lungs are still developing), those with weakened immunity or existing lung disease, and people who spend a significant amount of time outdoors, especially if doing physical activities.

Even short-term exposure (less than 8 hours) can exacerbate asthma and COPD, or cause those diseases to develop, reduce lung function, cause shortness of breath, and increase the incidences of lung infections. Ozone toxins are so potent that short-term exposure can also lead to mortality.


How to Protect Yourself from Ozone Pollution

Now that you know how damaging ozone pollution can be, you probably understand the necessity to protect your lungs from exposure. We’ve put together recommendations from top medical experts:

First and foremost, monitor the air quality in your area and use it as a guide. Many products and technologies now integrate BreezoMeter air quality data to ensure you can access the information you need. We also have a free app providing real time, geo-localized air quality data along with health recommendations.


  • When air quality is great, enjoy the outdoors, but when the air quality decreases:

  • If you can, stay indoors and keep your windows closed.

  • If you like to exercise outdoors, switch high-intensity exercises for easier ones

  • Keep your children and sensitive people inside

The Weekend Effect

Logical reasoning would bring us to think that street-level ozone is higher during the week than on weekends, as daily commuters emit pollutants that will react with VOCs and UVs to create ozone. Yet, studies have demonstrated otherwise: “bad” ozone is higher during the weekend, and scientists still haven’t agreed on a reliable explanation for the “Weekend Effect”, but here are two theories:


  1. Since ozone pollution in the lower atmosphere is a result of car emissions (nitrogen oxide and VOCs) mixed with sun and heat, there is a theory that on weekends, more cars are on the road around noon, when the temperature is at its peak. At that time, the elements needed to create ozone pollution are all there.

  2. During the weekend, the concentration of primary pollutants produced by human activities decreases. It is possible that those pollutants usually react with ozone thus reducing its concentration during the week. This phenomenon doesn’t happen in the same amount during the weekend, which could explain a higher concentration of ozone.

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