Viruses and Indoor Air Quality: Lessons from a Pandemic

March 2021

The pandemic has brought many reflections that a sociologist would analyse much better than us, but in our field of work it has clearly brought to the table the need to review the air we breathe in our enclosed spaces.

There is no magic wand for assessing and/or predicting the existence of a virus in an indoor space, its virulence and the risk of contagion that it may pose. However, scientific research and the recommendations of international organisations and bodies in this pandemic year provide evidence that leads us to understand how indoor spaces condition a lower or higher probability of virus spread.

SARS-CoV-2: airborne transmission

Defining a virus is a task for scientists. Pere Estupinya defines it in his programme El cazador de cerebros on 19 October 2020 "Investigando frente a la covid19 ": 

SARS COV2 is between 90 and 120 nanometres long, less than one thousandth of a human hair. Its genome is a strand of RNA with just ten coding genes - humans have around 20,000. And the proteins that wrap around it are like tiny needles reminiscent of the sun's corona - hence the name "coronavirus". And they're like Velcro. They bind to proteins in our cells called ACE2 receptors, which are key to the study of COVID, because they are the gateway for this virus to enter our body. It's like a sticky virus.

As we saw in our first pandemic post, the SARS-CoV-2 virus spreads mainly through small droplets - droplets and aerosols, which are released when a person coughs, sneezes, speaks, shouts or sings. The droplets infect by impact in the eyes, nostrils or mouth, within a radius of action of up to 1-2 m (hence the established safety distance).

These droplets cannot remain suspended in the air due to their weight, which means that they quickly fall to the ground or a nearby surface. In this sense, the survival of a virus on a surface depends on a multitude of factors, such as the type and nature of the surface and the temperature and humidity conditions of the space. This is one of the routes of transmission of SARS-CoV-2, contact by fomites, which has been losing ground to airborne transmission.

Smaller droplets travel further than larger droplets, and remain suspended in the air for longer in the form of aerosols. And it is these aerosols that infect by inhalation.

According to the article "A Rosetta Stone for Understating Infectious Drops and Aerosols" of July 2020, aerosols are classified according to where they are deposited in the respiratory tract into:

  • Aerosoles respirables o material particulado <2,5 μm (PM2,5) – que son los suficientemente pequeñas como para alcanzar los bronquiolos.
  • Aerosoles torácicos o partículas <10 μm (PM10) – de mayor tamaño y capaces de penetrar en la tráquea.
  • Inhalable aerosols or total suspended particulate matter (TSP), up to 100 μm in size.

"The aerosol fraction (respirable, thoracic or inhalable) that is most important from a health point of view depends on the pollutant and the tissue it affects. For a virus that uses a receptor on the surface of cells throughout the respiratory tract, all these aerosol fractions are likely to be important. Controlling and monitoring airborne particles will therefore help to assess indoor conditions.

Key parameters in indoor air quality monitoring in relation to the spread of viruses

In view of the above, the transmission of viruses in indoor spaces is complex and diverse. Apart from the biological parameters that define and condition them, the indoor space itself can condition their survival and propagation. Air renewal conditions are key and therefore knowing the effectiveness of ventilation through CO₂ concentration is the basic strategy. But equally, it will be necessary to know the conditions of indoor temperature, relative humidity and the presence of suspended particles, which as we have seen, can be the key vehicle in which viruses travel and spread in indoor spaces.

In our comfort range of 20-25°C and 40-60% relative humidity the virus is very stable. Studies have shown that low relative humidity (below 40%) favours its spread through the air and reduces the resistance of our immune system, so maintaining a well-humidified environment will always reduce the consequences of a possible contagion.

Our device MICA Lite continuously monitors these four parameters, to report on ventilation efficiency and the likelihood of virus spread in an indoor space.

What has the pandemic taught us?

This article suggests that improving indoor air quality (IAQ) and ventilation strategies could be as effective in reducing aerosol-borne virus transmission as vaccinating 50-60% of the population.

Headlines like this can have many nuances, but the truth is that this year has brought us important learnings as well as an awareness of the importance of indoor spaces in relation to our health. We have spent a year improving the environmental quality of our homes and work environments. And not just in the short term because of a viral pandemic, but in the medium and long term these actions have direct and beneficial repercussions for our health and that of our built environments:

  • Reduction in sick leave due to the influenza epidemic and other respiratory diseases.
  • Improving the efficiency of indoor ventilation systems.
  • Improved working conditions and the healthiness of the spaces, which results in an increase in the well-being of workers and users, and in the improvement of their attention span, productivity and performance in the work space.
  • Optimisation and flexibilisation of working hours.
  • Raising awareness of the need to incorporate natural elements in interior spaces, together with the promotion of semi-exterior spaces (patios, terraces, views, natural surroundings, etc.).

The challenge is that the awareness that has led us to take action to improve the indoor environment of our built spaces this past year will not be forgotten when this pandemic becomes a faded memory. Indoor air quality is a right today, it was yesterday, and it will be tomorrow.

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