Part 2: The logic and science behind Indoor Air Quality monitoring & management

2. COVID-19 - understanding viral infection potential in indoor environments

The direct impact that air quality and other indoor environmental factors have on human’s health, comfort, productivity has been well researched in the past. Based on these studies clear guideline has been established for indoor environments (as discusses in the preceding sections of this document).

However, in the wake of the global pandemic caused by COVID-19, during 2020 we have seen seismic changes to the way we live and work. As workplaces around the world sit empty, business leaders and buildings owners are frantically searching for answers.

How can we safely reopen these spaces, while keeping our employees safe from the spread of this deadly virus?

Other than the traditions offices and workspaces, the places that people need to visit as a matter of necessity - such as hospitals and shopping malls, and schools and educational institutions – also needs to be as safe as possible at all times. Amidst the COVID-19 pandemic, we need more than ever, to understand the critical role of indoor environmental quality, and specifically air quality plays in our quality of life and health. How do we discern if conditions in indoor environments might be ripe for viral survivability and spread?

Currently, there is no continuous air quality monitor that can detect viruses themselves. A virus is too small, no continuous monitoring sensor can measure at the level of granularity to identify specific viruses. Viruses are usually much smaller than bacteria with the vast majority being submicroscopic, generally ranging in size from 0.005 μm to 0.300 μm. Coronary viruses are spherical particles between 0.06 micron and 0.14 micron in diameter, with COVID-19 averaging about 0.125 microns, measured by electron microscope (Zhu et al, 2020).

A significant amount of research has been conducted on the complexities of airborne pathogens, how infections happen, the effects of air pollution, and also why certain conditions are hospitable for specifically viral survivability. Based on these studies, we can look at several of the indoor environmental parameters that help us understand air quality and get a view of infection potential for viruses. Air quality monitors gather data that can be used to determine the risk of potential infection in a certain space and whether it would be beneficial to implement some type of remediation action.

The five environmental and air quality parameters that have a role to play in determining the risk of COVID-19 surviving and spreading in indoor spaces are:

  • PM (particulate matter)

  • Temperature

  • Humidity

  • CO2 levels

  • TVOCs (Total Volatile Organic Compounds)

2.1.1 How they relate

Airborne particles of biological origin including bacteria, fungi and viruses, are commonly present in the air we breathe. Any respiratory pathogens able to remain viable (infectious) after aerosolization and air transport are a potential cause of respiratory disease, and they are often associated with other substances to form ‘complex particles’ (Tang 2009). Virus containing aerosols can be formed through natural occurrences, for example, sneezing by an individual harbouring a respiratory virus infection, or through mechanical means, for example, when air currents around contaminated surfaces disperse the viruses into the air (Verreault et al. 2008).

The dimensions of aerosolized virus particles vary widely, ranging from nanometre (e.g. ‘naked’ virus particles) to micrometre (e.g. viruses associated with nonviable particles) (Gerone et al. 1966). Once airborne, small particles containing virus(es) can remain airborne for long periods, allowing for their transport to other locations. Overall, smaller particles that contain respiratory viruses are potentially more dangerous because they stay airborne longer (and thus the risk for acquiring an infection is prolonged), and they get inhaled into the lower lungs, potentially causing diseases with more severe outcomes.

To date, several scientific studies focused on virus diffusion among humans demonstrated that increased incidence of infection is related to airborne particulate matter (PM) concentration levels. It is known that PM fractions (e.g., PM2.5 and PM10) serve as a carrier for several chemical and biologic pollutants, viruses included.

2.1.2. Recent research

Recent events and consequent studies suggested that high concentrations of PM of air pollution might favour the spread of COVID-19. Scientific works from around the globe have discussed the likelihood that high concentrations of PM may have been one of the major causes for the important outbreak that has hit several industrialised regions such as Wuhan and northern Italy. As a result, a cascade of works based on data analysis has emerged from around the world to address the question at hand.

PM and COVID-19 infection risk

On 20 March 2020, Setti et all published a study at the Italian Society of Environmental Medicine (SIMA), in which they found a linear relationship between PM10 levels above 50 microns / m3 and the rate of spread of COVID-19 in Italy. These results are fully consistent with scientific studies on the spread of viruses and bacteria in the population by suspended particles, which correlate the incidence of viral infections with the levels of atmospheric particles (PM10 and PM2.5). (Ciencewicki J. et al., 2007; Sedlmaier N., et al., 2009).

The Italian experience indicates a direct relationship between higher levels of particulate matter PM10-2.5 and higher levels of COVID-19. It found that at average PM10 levels of 350 μg/m3, the infection rate will be twice as high as at levels below 50 μg/. This is also the first evidence that SARS-CoV-2 RNA can be present on PM, thus suggesting possible use as an indicator of epidemic recurrence.

Historic PM exposure and COVID-19 mortality risk increase

Another study published in April 2020 by Wu et al, looked at that exposure to air pollution and COVID-19 mortality rates in the United States in a nationwide cross-sectional. Data sources COVID-19 death counts were collected for more than 3,000 counties in the United States (representing 98% of the population) up to April 22, 2020, from Johns Hopkins University, Center for Systems Science and Engineering Coronavirus Resource Center.

Results found that an increase of only 1 μg/m in PM is associated with an 8% increase in the COVID-19 death rate, and concluded that a small increase in long-term exposure to PM leads to a large increase in the COVID-19 death rate.

Extended PM exposure and decrease in defence against COVID-19 virus

Recent work by Conticini et al. stated that communities living in polluted areas (such as Lombardy and Emilia Romagna) are more predisposed to die of Covid-19 because of weakened health status. They claimed that a subject’s exposure to both PM2.5 and PM10 leads to systemic inflammation. This leads to a chronic inflammatory stimulus that weakens the cilia and upper airways defences and facilitates virus invasion by allowing the virus reaching lower airways.

PM exposure and infection risk

Travaglio et al. analyzed data collected in England and showed positive associations/correlations between the exposure to different air pollutants and the number of COVID-19 infections and fatalities.

COVID-19 fatality and PM count correlation

Ogen (2020) recently analysed data from 66 administrative regions in France, Spain, Italy, and Germany, and found that the highest COVID-19 deaths in these regions were associated with five regions of Northern Italy that also corresponded with the highest levels of atmospheric air pollution. Cole et al (2020) estimate the same relationship using Netherlands municipality data and find PM2.5 positively associated with COVID-19 cases, hospitalization, and deaths.


Worryingly, research links both long and short-term exposure to PM2.5 to a higher incidence of death from COVID-19. Additionally, it has also been established that PM fractions (e.g., PM2.5 and PM10) serve as a carrier for several chemical and biologic pollutants, viruses, COVID-19 included. Without any doubt, these studies put into light a correlation between air pollutants and COVID-19 cases.

2.2. Temperature and humidity

2.2.1 Virus survivability conditions

There is a body of evidence that connects virus survivability with cool, dry temperatures. Viruses tend to prefer cold and dry conditions - that’s why scientists put them in freezers to maintain them. At the same time, the opposite is true for the human immune system; it doesn’t perform at its best if exposed to prolonged cold, dry conditions. For example, sitting in a dry office space for eight hours a day, every day, is likely going to challenge your mucociliary function. Your nose and mucous membranes are going to be too dry and that might just open the door for infection.

2.2.2. Role in infection rate

A study by Ward et al (2020) found that dry air appears to favour the spread of COVID-19, and concluded that for a 1 per cent decrease in relative humidity, COVID-19 cases might increase by 7-8 per cent. The estimate is about a 2-fold increase in COVID-19 cases for a 10 per cent drop in relative humidity. Professor Ward said there are biological reasons why humidity matters in the transmission of airborne viruses. “When the humidity is lower, the air is drier and it makes the aerosols smaller,” he said, adding that aerosols are smaller than droplets. “When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.

2.2.3. Other threats to respiratory health

At the same time, as outlined in the WHO guidelines for ventilation in buildings it is important to understand that too high indoor humidity is associated with increased growth of microorganisms such as mould and bacteria (Institute of Medicine, 2004).

2.2.4. Recommended levels

The standard recommended ranges for office environments for temperature and humidity should be maintained (Temp 22-24C, Humidity 40% to 60%) for risk of viral survivability not to increase. Colder and drier conditions should certainly be avoided.

2.3. Indoor levels of CO2

2.3.1 CO2 as an indicator

Humans are the main indoor source of carbon dioxide (CO2) in most buildings. CO2 is a sign of stagnant air that has been expired from people’s mouths and lungs. By proxy, CO2 levels can alert us to over-crowded spaces with too little outdoor or cleaned air.

2.3.2. Increase in air-borne time-period

United States Environmental Protection Agency (EPA) published a statement confirming evidence that the COVID 19 virus can remain airborne for longer times and further distances than originally thought. In addition to close contact with infected people and contaminated surfaces, the spread of COVID-19 may also occur via airborne particles in indoor environments, in some circumstances beyond the 2 m (about 6 ft) range.

Unventilated air has a huge role to play in the viral Index. In addition to sneezing and coughing, viruses get release into the air through normal breathing. If people are infected, they will exhale not only CO2 but viruses as well. If you have sick people in the space, one can deduce that there are airborne virus particles in there too.

ASHRAE (American Society for Heating, Refrigerating, and Air Conditioning Engineers) released a statement recently on the airborne transmission of COVID-19:

Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.

2.3.3 Recommendations

To limit the possible transmission of viruses that become airborne as a result of human respiration, it is recommended that CO2 levels be kept below the accepted norm of 1000ppm, and preferably as low as 800ppm.

2.4. Exposure to VOCs

2.4.1. Knock-on effect

Of course, it isn’t just COVID-19 itself that is jeopardizing our health – the virus has triggered indirect risks and consequences too. It led to a hike in indoor air pollution within our homes and workplaces. And this was partly because we were cooking and cleaning more than ever within a confined space. Now, as we figure out how we can safely return to the workplace, we need to be mindful that our enhanced, COVID-secure cleaning regimen may have an impact on the air we breathe there too.

2.4.2. Displaced health risks

We are all washing our hands and hyper-cleaning our surfaces, and in some cases, those staff who are responsible for cleaning are potentially being exposed to a new quantity of VOCs. While cleaning used to happen after the building was closed, when occupants had vacated the premises, we are now literally wiping down surfaces on top of people. “But by continuously monitoring the levels of TVOCs in a space, we can alert ourselves when we may be putting the occupants in a more precarious position. The last thing we want to do is increase our exposure to harmful VOCs, and monitoring will tell us when the levels are high and require further inspection. If VOCs from industrial cleaners that contain chemicals of concern is accumulating in an enclosed space, then that might need attention. This is the responsibility of every employer to protect their occupants, maintenance and cleaning staff as long term exposure to harmful VOCs can be detrimental to the health of individuals.

2.4.3. Recommended levels

It is recommended that VOCs levels be kept between 0.3 to 0.5 mg/m3 or 200 PPB.

The future of the indoor & workspace

So, as we try to work out how to give our employees peace of mind, what does the future of the indoor & workplace look like? Of course, it’s highly likely that people occupying a space- whether an office, restaurant, shop, lecture hall – will demand transparency, so they know the air quality is being closely monitored and controlled.

“People will want the buildings they inhabit to support their wellbeing more than ever before,” says Anjanette Green, the Director of Standards Development at RESET, “That’s not a nice-to-have, it’s a must-have. Life as we know it has changed and the spaces we inhabit need to prioritise our health and wellbeing. I’m talking about real changes that will fundamentally help people remain safe. And this isn’t just about COVID-19, because there will be more emergencies in the future – perhaps another pandemic, smoke from raging wildfires or increased air pollution caused by global warming. “Increasingly, we will rely on our buildings to protect us, and that means we need to start using building data to drive our course of action and create better, more holistic reactions, no matter what the event.”

Click here to read Part 1 of our research.


1. Zhu et al, (2020) A Novel Coronavirus from Patients with Pneumonia in China, The New England Journal of Medicine.


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