Indoor Air Quality and Airborne Disinfection for Schools

As the first horrific phase of Covid-19 appears to be hitting its peak in the hardest hit areas of our country, scientists are worried about the second wave of this notorious pandemic. It could potentially crash worse than the first hit, killing thousands more in its wake. While there is no crystal ball to look into the future of what the second phase might look like, one of the main topics on many people’s mind is what does our “new normal” look like? With the pandemic already closing nearly all U.S. schools for the remainder of the year, many of our politicians are stating that reopening our schools and getting our children back in the classroom is a cornerstone of our economy trying to find it’s new normal. 

Since the illness is transmitted via airborne droplets that can stay viable for many hours, our attention needs to turn towards how to keep the air in our schools systems as clean as possible. As our children return to school and the word begins to re-emerge,  “Indoor Air Quality”, or IAQ should be top of mind – not only for parents of children returning to school in the fall, but for administrators and superintendents concerned about the health of their staff.  According to the Environmental Protection Agency, “Indoor Air Quality (IAQ) refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants. Understanding and controlling common pollutants indoors can help reduce your risk of indoor health concerns.” To really understand the role that IAQ plays in the coronavirus pandemic, it’s important to understand some science around how this disease (and many others) spread. 

Indoor air pollutants fall into several different categories and stretch a wide range of different contaminants, but when it comes to infectious disease in school systems, and specifically with the focus of Covid-19 in mind,  we will take a closer look at two general categories: bioaerosols and droplet nuclei.



According to Lennox, “Bioaerosols, or biological aerosols, are tiny airborne particles that are biological in nature. That means they either come from a living organism (such as dander from indoor pets or pollen from trees) or are living organisms themselves (such as bacteria and viruses).” COVID-19, influenza and other viruses are living organisms, and, by definition, fall into the category of bioaerosols.

Bioaerosols are small enough to fit through filters and can double, under ideal conditions, every twenty minutes. 


Droplet Nuclei

According to the Center for Disease Control (CDC), droplet nuclei can be defined as, “Droplet nuclei are dried residue of less than 5 microns in size. In contrast to droplets that fall to the ground within a few feet, droplet nuclei may remain suspended in the air for long periods of time and may be blown over great distances.”

With that said, understanding how bioaerosols and droplet nuclei spread from person to person, is important in understanding how to mitigate the risk of infection. Typically, larger droplets fall to the ground rather quickly, but smaller droplets evaporate and move on to become droplet nuclei. This droplet nuclei can remain suspended in the air for hours or even days, traveling long distances or recirculating with a building envelope through the HVAC system.  The illustration below shows how a 2um droplet nuclei settling in a calm room, much like that of one of our nation’s classrooms, takes approximately 4.2 hours to fall a distance of 2m. The presence of viral RNA in air droplets and aerosols indicates the possibility of viral infection.

As scary as it sounds, one simple cough can generate 3000 droplet nuclei, while something as simple as talking can generate the same amount. Sneezing, which we know school aged children are notorious for and most often fail to do so into their elbows, generates tens of thousands of droplet nuclei, which can spread to individuals up to ten feet away.  



By now we all know our way around what Covid-19 and understand that this is primarily a respiratory virus. This virus is spread via respiratory droplets (droplet nuclei) and viciously attacks the lungs and the immune system. We also know that Covid-19 kills via secondary infections much like influenza and as we learn more about it, we are learning that the secondary infections are all across the board – from pneumonia, to blood clots to most recently, strokes. Knowing this, it’s fair to say that the less airborne the viral load is and secondary infections that occur translates to an increased survival rate.  The goal needs to be slowing the airborne spread.


Enter UVGI Lighting Solutions

There’s been a lot of talk in the news lately about how ultraviolet germicidal light (UVGI) can destroy the virus. This method is a simple and effective way to curb not only viral growth, but bacterial growth as well. As a technology, ultraviolet light disinfection has been around for a while. UV light shows a lot of promise – with a 99.9% sterilization of coronavirus (COVID-19) in 30 seconds”. Using this technology in the classroom to control IAQ, may just be our answer. According to ASHRAE, “UVGI can be effective in reducing the virulence of microorganisms and therefore reducing infection rates. “ (ASHRAE, 2.11: Ultraviolet Radiation”. The integration of UV in the wise approach to airborne disease mitigation for an entire school building – the final product a biologically effective way to control the spread of the virus.  


The Research

Several schools and universities have installed UV lighting in their office ventilation systems and saw significant eradication of viruses and a significant decrease in absenteeism among staff and students. This study from McGill University is worth the time to read if you are considering installing UV lighting in your institution. 

McGill University UVGI Study:

  • Operation resulting in 99.9% reduction of microbial and endotoxin concentrations on irradiated survases within the ventilation system
  • Use of UVGI was associated with significantly fewer work-related symptoms overall
  • 26% overall reduction in absenteeism


To learn more about how installing UVGI lighting in your school can affect the overall indoor air quality in your institution and slow the spread of COVID-19, check out our latest webinar:


Hughes Environmental is built to handle the COVID-19 threat and deliver our services and products when it counts. We consider it our responsibility to make sure each and every business is code compliant and infection-free. Our customers should not have to fear working in unsafe conditions and that is why we are offering 24/7 service to meet any COVID-19 responses.

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