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Aerosols – The tiny travelers with a big influence

This is the second article from our “25’000 – every breath counts – Importance of Indoor Air Quality Monitoring in Hotels” – ARVE series.

Aerosols. We have all heard about them in the past few months. But what are they? And why do hoteliers have to know about them?

This is what we try to answer in this short article:

Take a deep breath. Now think about what you just inhaled. Air, right? But it is not as easy as that: research proofs that you just inhaled several thousand* of solid particles and liquid nano drops. Those are known as aerosols.

Size comparisons for PM particles
Source: US EPA

Scientists define an aerosol as a suspension of particles in the atmosphere. Small in size, they are 10 to 25 times smaller than human hair (see image 1) and have both human-made and natural sources.

Despite their small size, they have significant impacts and our health. Research showed that in addition to smear infection (from surfaces), aerosols are considered to be an important transmission route of Sars-CoV-2.

How aerosols contribute to indoor transmissions

Among other things, an aerosol can be a fluid particle of saliva or respiratory fluid that floats in the air and infects us when we breathe it in. Both aerosols and droplets are generated by people when they cough, talk, or sing. The main differences from aerosols to a droplet are: A droplet floats in the air and can infect us when it hits our eyes, nostrils, or mouth, whereas an aerosol can result in airborne transmissions through breathing.

Droplets are larger** and therefore, they fall to the ground by gravity. Whereas aerosols are much smaller** and thus, they remain in the air for several hours and can travel way further than droplets, which is the reason for airborne transmissions. Furthermore, viruses on aerosols remain infectious for several hours (1).

Even though aerosols' role in the overall transmission scheme is still challenging to quantify, superspreader events indicate that aerosols are a crucial transmission mode in indoor situations, where low indoor air quality can increase the risk of airborne transmissions. This is because rooms with poor indoor ventilation allow aerosols to remain in the air for longer (1).

So why is this important to know for hotels?

In hotels, guests spend 90% of their time in indoor environments. They are sleeping, eating, or otherwise spending time in their rooms. As already mentioned in our last article, it is crucial for hotels to monitor indoor air quality and ensure a healthy environment for guests and staff.

The common safety measures such as regular cleaning and disinfection of surfaces, mandatory masks, and physical distancing are valuable for both, aerosol-based and droplet-based transmissions. But a few critical additional measures should be taken by hotels to reduce the risk of infections with SARS-CoV-2 even more.

  • Ensuring proper ventilation in the guest rooms and common areas (either with fresh air, or where not possible with properly filtered and non-recycled air) (1), so the proportion of rebreathed air remains as low as possible. The objective is to reduce the time that aerosols and droplets remain airborne and maintain aerosols' concentration in the air low (1). A healthy ventilation condition is characterized by a CO2 concentration < 800 ppm, which also offers the best approach to reducing the aerosol load in the room (6).

  • Avoid overcrowding of common areas and back of house offices.

  • In case air can flow between the rooms, hotels should try to block the route or should not assign those rooms to guests.

  • In addition to these measures, monitoring the air quality and taking appropriate steps to avoid poor indoor air ventilation situations is exceptionally effective.

Clean air as the new amenity?

With the new air-awareness spreading among travelers, many hotels are starting to invest in expensive air filtration and air treatment systems to scrub the air their guests breathe as clean as possible. The objective is not only to keep guests safe, but it is primarily to reassure them that the air they breathe is healthy. However, there are downsides to those systems, such as the introduction of ozone. Instead, many experts recommend increasing the ventilation with outdoor air and closely monitoring the air quality before investing essential resources in air ventilation systems (4). Many times, higher rates of airflow can do the trick.


Even though they are so small, the human eye cannot even see them; aerosols play a significant role in transmitting COVID-19 infections. Therefore, hotels must understand why it is vital to consider airborne transmissions when creating their safety measures. Good indoor ventilation and monitoring of the hotel's air quality are the two most important actions for every hotel to provide a safe and healthy environment for guests and staff.

At ARVE, we support you where it matters, and that is reassuring your guests that they can feel safe in your hotel. The ARVE Swiss Air Quality System allows you to not only know the air quality for each room in real-time, but it also gives you actionable insights to make smart management decisions. And that, before investing in expensive technologies to clean your air.

Did you know? The average human takes 25'000 breaths each day. Let's make them count for you and your hotel.

Stay tuned for our next article about “AQI – What does it mean and why is it important in hotels?” in the “25’000 – every breath counts – Importance of Indoor Air Quality Monitoring in Hotels” – series.

#arve #airquality #aerosols #airquality #ventilation #covid19 #transmission #air #arveswiss

*Typical air has around 20’000 to 100’000 particles in a breath (if a breath is assumed to be 1 liter of air inhaled)

**Here a quote from a Policy Brief from the Switzerland National COVID-19 Science Task Force (NCS-TF) (2020) “It is important to highlight that “larger” and “smaller” droplets are part of a continuum of droplet sizes. There is thus no clearly defined cut-off in size that distinguishes two separate classes of droplets. Rather, the effect of gravitational settling (i.e., falling to the ground) increases with increasing droplet size, whereas the effect of evaporation (which shrinks the droplet size) increases with decreasing droplet size.”


1. Stocker, R., & Sutter, S. et al. (2020, October 29). National COVID-19 Science Task Force (NCS-TF) [Pdf]. Zurich: National COVID-19 Science Task Force (NCS-TF).

2. Scientific brief: Sars-cov-2 and potential airborne transmission. (n.d.). Retrieved February 19, 2021, from

3. Aerosols: Tiny particles, big impact. (n.d.). Retrieved February 19, 2021, from

4. Glusac, E. (2020, December 03). The newest hotel Amenity? VIRUS-SCRUBBED AIR. Retrieved February 19, 2021, from

5. Particulate matter (pm) basics. (2020, October 01). Retrieved February 25, 2021, from

6. Stellungnahme: Aerosole & SARS CoV2 – Entstehung, Infektiosität, Ausbreitung & Minderung luftgetragener, virenhaltiger Teilchen in der Atemluft. (2020, December 04). Retrieved February 23, 2021, from

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