Indoor Ozone: 3 Common Sources Explained

While usually thought of as an outdoor air pollutant, ozone is becoming an increasing concern indoors as well. Certain pieces of technology have the capacity to produce ozone, which has repercussions for employees and employers alike. 

Beyond ozone itself, chemical reactions between ozone and other air pollutants such as formaldehyde can produce secondary pollutants, including particulate matter. Clearly, it’s important to be aware of indoor ozone and take steps to eliminate it if necessary. We’d like to discuss all the potential sources of indoor ozone that you should know about, as well as look at some ways to ensure indoor ozone remains at safe levels. 

Outdoor Sources of Ozone

Perhaps unsurprisingly, most indoor ozone originates from the outdoors. 

Ozone is a secondary air pollutant, meaning that most of it comes from chemical reactions between other air pollutants, including volatile organic compounds and nitrogen oxides, in the presence of sunlight. These same reactions also produce photochemical smog, which is a common occurrence in cities during the summer.

Like particulate matter, ground-level ozone can seep into buildings and offices through doors and windows, or through the ventilation of outdoor air. 

Indoor Sources of Ozone

Besides ambient ozone that can seep into offices, there are a few specific sources of ozone that are strictly indoor. Indoor ozone emission devices, or IOEDs, include air purifiers, disinfectors, laser printers, photocopiers, and others. 

Air purification devices

While it may seem ironic, some types of air purification devices can also produce ozone, either as a byproduct or intentionally. 

Let’s begin with ionizing technology. Ionizers emerged as a popular alternative to HEPA purifiers, as they have lower maintenance costs, and in some cases, ionization technology can easily be incorporated in HVAC systems without changes in pressure drop or filtration efficiency. Ionization utilizes an electrical charge to create both positive and negative ions, in the case of bipolar ionization, or just negative ions. These ions can be beneficial for removing particulate matter and volatile organic compounds (VOCs), but the process also has the potential to create ozone. 

Another common form of air purification and disinfection is ozone generation. In this case, ozone is created directly for the purpose of breaking down air pollutants and airborne microbes. Needless to say, ozone generators are capable of raising indoor ozone levels to severely unhealthy levels, and should never be used around building occupants. 

HEPA purifiers and UV light (when used at the appropriate wavelength) do not produce ozone. 

Laser printers and copy machines

Laser printers and photocopying machines produce less ozone than ozone generators and ionizers, but they can be a problem in enclosed spaces. 

Laser printers and photocopiers have both been found to create indoor air pollution, including ozone, volatile organic compounds, semi-volatile organic compounds, and heavy metals. Ozone is a by-product of the electro-photographic process, and these devices usually only produce ozone during operation, when the coronas are energized. For this reason, as well as contributions from ambient pollution, indoor ozone levels tend to be higher during working hours, which can impact employees. 

How To Maintain Safe Indoor Ozone Levels

To control ozone in your indoor air, it’s best to take a three-pronged approach.

1. Limit the introduction of ambient ozone by keeping doors and operable windows closed on polluted days. Ozone can be removed from ventilated air with activated carbon filters, which absorb ozone from the air passing through the HVAC system. 
2. Eliminate or consolidate indoor sources of ozone. For example, isolate photocopiers and laser printers away from employees in a central location to avoid consistently exposing them to ozone. 
3. Monitor indoor ozone levels to ensure that building occupants are safe at all times. 

Bipolar ionization, a type of air purification technology that has surged in popularity during the COVID-19 pandemic, can potentially be a source of indoor ozone, as well. Find out more about bipolar ionization, how it works, how it can help during the pandemic, and if it is safe to use: Can Bipolar Ionization Technology Help Eliminate COVID-19?

Kaiterra provides air quality monitors and an IAQ analytics dashboard for healthy buildings and offices, helping workplace leaders and healthy building pioneers assess and improve their indoor air quality. Our indoor air quality monitors like the Sensedge and the Sensedge Mini can be found in many of the world’s most iconic buildings and workplaces, such as the Empire State Building and the Burj Khalifa.