Humanity is currently facing an invisible threat that is several times smaller than a single strand of hair. In under three years, COVID-19 has brought critical awareness to aerosol particle transmission, which has drastically altered the way we live and interact with one another. We know that the virus can infect us at almost any moment, but we cannot actually see the hazard. How do we protect ourselves and our communities when senses such as sight are useless in assessing this risk? The answer may lie in seeing the unseen.

As a scientist, I am used to making the invisible become visible. In my research, I have used electron microscopes to probe samples to capture images of particles that are a fraction of the diameter of a strand of hair. The samples I image include aerosol particles, solid or liquid droplets suspended in air that vary in size with most so small they cannot be seen without the aid of microscopes. Aerosol particles are significant for many reasons; one being that clouds would not form without them, another, the spread of COVID-19 and other viruses. Visually seeing aerosol particles that are too small for the human eye to detect makes me acutely aware of their presence in the surrounding air.

During 2020, I started hearing aerosol particles mentioned outside of the atmospheric science field. News sources in late 2019 began reporting the invisible threat of COVID-19 with limited ideas of how it was spreading. Headlines would pose the question – “could it be transmitted through the air conditioning?” I imagined fluorescent green goo seeping through vents infecting people. It was like a horror movie, a terrible illness spreading quickly with no apparent direct contact.

The dangers of sharing air were amplified after every report of mass infection following gatherings, such as choir practice where groups projected not only their voices into the room but also their infected particles. Now, more than two years into the pandemic, aerosol particles have now been well-established as the main mode of COVID-19 transmission.

We can fight against this invisible threat with the new understanding and knowledge that aerosol particles containing the virus are in the air and contributing to the spread COVID-19. Establishing the main source of transmission has given us the ability to better direct public health policies. The data are clear that improved air ventilation and filtration can help rid the air of the virus and thereby reduce transmission.

Ventilation and air filtration: Science-backed practices to reduce COVID-19

Recent scientific studies further support that the inhalation of aerosol particles produced by infected individuals is the main mode of COVID-19 transmission. While the threat of COVID-19 remains unseeable by the naked eye, we can now perceive it due to the established knowledge of aerosol particles. Not only is detecting aerosol particles possible but it also allows us to determine how to reduce transmission risk.

Clearing the air by increasing ventilation and air purification can reduce the number of infected aerosol particles in indoor spaces and add another layer to COVID-19 risk mitigation. The benefits of establishing better indoor air quality practices extends beyond the current pandemic. Measles, tuberculosis, and chicken pox are also all transmitted through aerosol particles and similar evidence is building for smallpox, influenza, SARS, MERS, and rhinovirus. Improving ventilation and air purification will have an overall benefit of reducing risk of infection for a multitude of illnesses. Indoor air quality is also significant for general health; 3.2 million premature deaths occur globally each year due to household air pollution.

There are several science-backed ways to improve air quality through ventilation and air purification. For example, ventilation introduces fresh outdoor air into an indoor space such as through opening a window. Placing a fan in a window to push out the indoor air while having additional windows open can increase the ventilation and further reduce infected aerosol particle concentration. Heating and HVAC systems can also be used to increase ventilation. There is a tradeoff, however, as it can lead to higher energy costs especially during colder months. Heat recovery systems can be put in place to minimize operating costs and any changes to operations of existing systems should be discussed with facility managers.

Carbon dioxide (CO2) monitors are a relatively inexpensive method to estimate the concentration of COVID-19 aerosol particles since individuals exhale CO2 at the same time as aerosol particles. The CDC recommends the benchmark of under 800 parts per million (ppm) to determine proper ventilation. Placing the CO2 meter in occupied spaces will help evaluate the delivery of outdoor air and can be used to assess risks based on real time CO2 concentrations. 

Cleaning indoor air through sterilization and filtration has the same effect as introducing outdoor air through ventilation. Upgrading filters in HVAC or furnace systems can improve the removal of aerosol particles. Look for filters that are either HEPA (High Efficiency Particulate Air) or have a minimum MERV-13 rating.

Portable air filters are extremely effective in removing aerosol particles. Placing several small units in indoor spaces such as classrooms can greatly reduce the risk of COVID-19 transmission. For an idea of cost, I use several HEPA air purifiers in my home. Each purifier can cover a room approximately 150-200 square feet in size and cost approximately $6/month to run nonstop. Homemade air purifiers, referred to as the Corsi-Rosenthal box, are an affordable option that uses box fans and furnace filters to create a highly effective system for removing aerosol particles.

There currently are funds available to education institutions to improve indoor air quality. Schools can use American Rescue Plan (ARP) funding to cover multiple approaches to improving indoor air quality. Higher education institutions can use Higher Education Emergency Relief (HEER) funds to improve ventilation. The Inflation Reduction Act includes new funds to improve indoor air quality in homes.

Improving indoor air quality needs to be an ongoing effort even once the systems are in place since filters will need to be replaced and systems will require maintenance. Implementing long-term planning is an important aspect of mitigation strategies to reduce COVID-19 risk and transmission of other airborne viruses. For instance, NYC schools pushed forward an emergency measure in August 2022 to spend $27 million for replacement filters for air purifiers purchased in 2020 in response to the pandemic. Keeping up with improved indoor air quality is important and maintenance requirements should be predetermined to include into future planning to avoid unforeseen expenditures. 

Individual and community response to COVID-19

Individuals are being called to make choices to help curtail the spread of COVID-19. We are provided with a mountain of information to help make choices that will hopefully keep ourselves and others safe. Living in a pandemic for over two years has already had major implications on our mental health and stress levels. Many of us are beyond capacity and burnt out to stay updated on the latest information and incorporate assessing personal risk into our lives.

The decrease in our motivation to fight the pandemic at an individual level is understandable as it is exhausting to carry the burden alone. Community engagement and organizational response are therefore critical in responding to the pandemic. The difference between an individual acting alone versus in a collection is that a community can offer support to ease the burden of carrying the responsibility completely solo.

It is in our best interest to combine ventilation and air filtration responses at both an individual and community level. We as individuals will still need to make risk assessments due to current guidelines. The communities we live in, however, can make it easier for us to make those decisions. Imagine if upon walking into the local store, there was a CO2 monitor with signage indicating that under 800 ppm CO2 is a good marker for good ventilation. In that space, individual risk assessment became easier because the information was both readily available and put into context without requiring previous knowledge. Another example is coming into work and being able to assess the state of the air filtration because there is a chart on the wall detailing when the filter was last replaced. Additionally, on the chart is information about the timeframe that filters have optimal functioning and a phone number to report past due filters.

In both scenarios, we are called to act as individuals but this time we are supported by a community. The weight to do all of the heavy lifting, such as researching important parameters or personal tracking, was shifted to the community which reduced the personal burden. I can picture a world where the ventilation and air filtration of businesses are given a rating and publicly posted much like a restaurant inspection.

There are multiple ways to address indoor air quality in response to a pandemic with responses ranging from low-cost options such as CO2 monitors and tracking filter replacements to high-cost options which include tackling infrastructure by installing improved air systems. I encourage community leaders to implement these approaches that will arm individuals with accessible tools to tackle airborne transmission of COVID-19.