Humanity is currently facing an invisible threat that is many times smaller than a single hair. In less than three years, COVID-19 has brought about a critical awareness of aerosol particle transmission, which has dramatically changed the way we live and interact with each other. We know the virus can infect us almost at any time, but we can’t actually see the danger. How do we protect ourselves and our communities when senses like sight are useless to assess this risk? The answer may lie in seeing the invisible.
As a scientist, I’m used to making the invisible 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, airborne solid or liquid droplets that vary in size, most being so small that they cannot be seen without the aid of microscopes. Aerosol particles are important for many reasons; one being that clouds wouldn’t form without them, another, the spread of COVID-19 and other viruses. Visually seeing aerosol particles too small to be detected by the human eye makes me very aware of their presence in the surrounding air.
In 2020, I started to hear aerosol particles mentioned outside the realm of atmospheric science. In late 2019, news sources began reporting the invisible threat of COVID-19 with limited insight into how it was spreading. Headlines would beg the question – “could it be transmitted through air conditioning?” I imagined fluorescent green slime seeping through the vents infecting people. It was like a horror movie, a terrible disease spreading rapidly with no apparent direct contact.
The dangers of air sharing were amplified after each report of mass infection following gatherings, such as choir practice where groups not only projected their voices into the room but also their infected particles. Today, more than two years into the pandemic, aerosol particles are now well established as the primary mode of transmission for COVID-19.
We can combat this invisible threat with the new understanding and knowledge that aerosol particles containing the virus are in the air and are contributing to the spread of COVID-19. Establishing the main source of transmission has allowed us to better direct public health policies. The data clearly shows that improved air ventilation and filtration can help clear the air of the virus and thus reduce transmission.
Ventilation and Air Filtration: Science-Based Practices to Reduce COVID-19
Recent scientific studies further confirm that inhalation of aerosol particles produced by infected people is the main mode of transmission of COVID-19. While the threat of COVID-19 remains invisible to the naked eye, we can now perceive it through established knowledge of aerosol particles. Not only is the detection of aerosol particles possible, but it also allows us to determine how to reduce the risk of transmission.
Purifying 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 extend beyond the current pandemic. Measles, tuberculosis and chickenpox are also all transmitted by aerosol particles and similar evidence is mounting for smallpox, influenza, SARS, MERS and rhinovirus. Improved ventilation and air purification will have the overall benefit of reducing the risk of infection for a multitude of diseases. Indoor air quality is also important for general health; 3.2 million premature deaths occur each year worldwide due to household air pollution.
There are several scientific ways to improve air quality through ventilation and air purification. For example, ventilation introduces fresh outside air into an interior space, such as by opening a window. Placing a fan in a window to expel indoor air while having additional windows open can increase ventilation and further reduce the concentration of infected aerosol particles. Heating and HVAC systems can also be used to increase ventilation. There is a trade-off though, as this can lead to higher energy costs, especially in colder months. Heat recovery systems can be put in place to minimize operating costs and any changes to the operations of existing systems should be discussed with facility managers.
Carbon dioxide (CO2) monitors are a relatively inexpensive method of estimating the concentration of COVID-19 aerosol particles since individuals exhale CO2 at the same time as aerosol particles. The CDC recommends the benchmark of less than 800 parts per million (ppm) to determine adequate ventilation. Placing the CO2 meter in occupied spaces will help assess outside air intake and can be used to assess risk based on real-time CO2 concentrations.
Cleaning indoor air by sterilization and filtration has the same effect as introducing outdoor air by 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 at removing aerosol particles. Placing multiple small units in indoor spaces such as classrooms can significantly reduce the risk of COVID-19 transmission. For an idea of cost, I use several HEPA air purifiers in my house. Each purifier can cover a room of around 150-200 square feet and costs around $6/month to run uninterrupted. Homemade air purifiers, called Corsi-Rosenthal box, are an affordable option that use box fans and oven filters to create a highly efficient system for removing aerosol particles.
Funds are currently being made available to educational institutions to improve indoor air quality. Schools can use American Rescue Plan (ARP) funding to cover several approaches to improving indoor air quality. Higher education institutions can use HEER (Higher Education Emergency Relief) funds to improve ventilation. The Curbing Inflation Act includes new funds to improve indoor air quality in homes.
Improving indoor air quality should be an ongoing effort, even after systems are in place, as filters will need to be replaced and systems will require maintenance. Implementing long-term planning is an important aspect of mitigation strategies aimed at reducing the risk of COVID-19 and the transmission of other airborne viruses. For example, schools in New York advanced an emergency measure in August 2022 to spend $27 million on replacement filters for air purifiers purchased in 2020 in response to the pandemic. It is important to track improvement in indoor air quality and maintenance requirements should be pre-determined for inclusion in future planning to avoid unforeseen expenses.
Individual and community response to COVID-19
Individuals are called upon to make choices to help stop the spread of COVID-19. We receive a mountain of information to help us make choices that will hopefully keep us and others safe. Living in a pandemic for over two years has already had a major impact on our mental health and stress levels. Many of us are beyond our abilities and exhausted to stay up to date on the latest information and incorporate personal risk assessment into our lives.
The decline in our motivation to fight the pandemic at the individual level is understandable as it is exhausting to bear the burden alone. Community engagement and organizational response are therefore essential to respond to the pandemic. The difference between an individual acting alone versus a collection is that a community can offer support to ease the burden of carrying the responsibility completely solo.
It is in our interest to combine ventilation and air filtration responses at the individual and community level. As individuals, we will still need to carry out risk assessments due to current guidelines. However, the communities in which we live can make it easier for us to make these decisions. Imagine if upon entering the local store there was a CO2 monitor with signage indicating less than 800 ppm CO2 is a good marker for good ventilation. In this space, individual risk assessment became easier because information was both readily available and put into context without requiring prior knowledge. Another example is arriving at work and being able to assess the condition of the air filtration as there is a chart on the wall detailing when the filter was last replaced. In addition, the graph contains information on the period during which the filters work optimally and a telephone number to report overdue filters.
In both scenarios we are called to act as individuals but this time we are supported by a community. The burden of doing all the heavy lifting, like finding important metrics or personal tracking, was shifted to the community, reducing the personal burden. I can imagine a world where companies’ ventilation and air filtration are rated and published publicly, much like a restaurant inspection.
There are several 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 that include addressing infrastructure by installing improved air systems. I encourage community leaders to implement these approaches that will equip individuals with accessible tools to combat airborne transmission of COVID-19.
Comments are closed.