Measurement of indoor air quality: what the coronavirus is teaching us

It is evident that pandemics, beyond the scientific and medical advances they provide, do not bring any benefit.

However, in the present case, perhaps a slightly positive aspect can be extracted. Because, in the end, the coronavirus is highlighting the importance of indoor air quality and, by extension, outdoor air quality. Understanding the relationship between pollution and health is a significant advancement in the field of public health.

How is indoor air quality measured?

If you are someone who follows the news, you have probably heard or read about the importance of ensuring good indoor air quality. In fact, viruses tend to thrive in enclosed spaces with high population density and poor ventilation. And considering that we spend approximately 80 to 90% of our time indoors, all these factors can only lead to problems.

So far, much of the media attention has been focused on schools. However, indoor air quality is a concern that should apply to all types of premises: offices, healthcare centers, hospitals, public buildings, etc. Now, what variables should be considered as a minimum to ensure good indoor air quality?

Carbon dioxide (CO2), temperature, humidity, and occupancy level of a room – 4 factors to consider

First and foremost, we want to make it clear that the solutions we propose alone will not stop viruses (including the coronavirus or any other microorganism present in the atmosphere). Therefore, it is necessary to implement other hygienic and sanitary measures for their containment. In this sense, sensors that can be installed in a room are a complement, an aid. Their main objective is to provide information about the environmental conditions of a closed space and alert the need to implement measures to improve air quality (such as opening windows, adjusting air conditioning systems, inspecting air filters, etc.).

With this detail clarified, let’s see which variables should be taken into account to create an atmosphere that hinders the spread of microorganisms.

Carbon dioxide (CO2), a fundamental indicator

Carbon dioxide (CO2) is one of the main indicators to assess indoor air quality. After all, it is a gas that we produce and exhale as a result of our metabolism. Therefore, when CO2 levels are high, it may indicate poor ventilation in a room. For example, in schools and in accordance with the UNE-EN 13779 standard and the Regulations of Thermal Installations in Buildings (RITE) (2), it is recommended that the concentration does not exceed 500 parts per million (ppm) above the outdoor CO2 level (around 400 ppm). In other words, the advice is not to exceed 900 ppm. However, considering the current situation, which is far from normal, it is better to err on the side of caution and not exceed 700 ppm (paragraph corrected as of 22/02/2021).

For instance, at Arantec, we are working with the Sabadell City Council to monitor the concentration of CO2 inside public buildings. For measurement, we use compact sensors strategically placed and connected via LoRaWAN, transmitting real-time information to our platform, facilitating decision-making.

Sensor ELSYS para medición de la calidad del aire en interiores

In the following video, which is from a school near Paris, you can see how the installation of sensors is allowing authorities to monitor, in addition to CO2, other types of compounds.

Humedity and temperature, two important variables in virus transmission

Humidity and temperature are two variables that go hand in hand. Especially in winter, it is common to find indoor spaces with a comfortable temperature but very low relative humidity. And according to data, these conditions are not the most suitable when it comes to reducing the transmission capacity of a virus.

In the case of the coronavirus specifically, there are still more questions than answers. However, based on what we know about the behavior of other respiratory viruses, it is estimated that transmission is easier when the relative humidity is below 40% (3, 4). Likewise, regarding temperature, it is recommended to keep it within a range of 20 to 24 ºC (5).

However, as we mentioned, there are conflicting opinions regarding the impact of these variables. For example, the Association of Air Conditioning Equipment Manufacturers (Afec) claims that they do not have a practical effect due to the resistance of coronaviruses to environmental changes.

Presence of people in an enclosed space

One of the main measures to combat the pandemic is limiting the capacity of indoor venues. The goal is to reduce the number of people to minimize the chances of transmission.

For this reason, sensors that monitor the occupancy of a space can also be a useful tool. The detection of people’s presence can be done through movement or by detecting the heat emitted by the human body. Thus, their installation could complement CO2 sensors, for example.

When indoor air quality affects performance

So far, we have focused on monitoring the environmental conditions that facilitate or hinder the spread of viruses. After all, that’s what is currently relevant.

However, indoor air quality also affects work or educational performance. According to a survey conducted in 2016 by the Building Engineering Services Association (BESA) in the UK, 70% of respondents reported experiencing a loss of productivity due to the habitual environmental conditions they were exposed to.

In fact, fatigue, loss of concentration, or headaches are symptoms that often indicate the need to improve ventilation in an enclosed space. For example, MacNaughton et al. estimated that improving ventilation systems by investing less than $40 per person per year resulted in a productivity improvement equivalent to $6,500 per year (6).

But there are also other factors that impact academic or work performance.

Lighting and noise, two variables with a direct effect on performance

Visual comfort, in terms of lighting conditions, and noise pollution have a negative impact on the effectiveness of an activity.

Regarding lighting, it will depend on the nature of the work or the age of the employees. However, to give you an idea of the benefits that monitoring can bring, here are a couple of data points extracted from a 2018 report by the Buildings Performance Institute Europe (BPIE) (7):

  • Every 100 lux improvement in lighting in schools is associated with a 2.9% increase in educational performance.
  • In offices, every 100 lux increase in lighting level enhances worker performance by 0.8%.

Regarding noise, current legislation (8) establishes acoustic quality indexes ranging from 30 to 35 decibels, varying according to the activity or type of space. However, it is important to note that the response to noise is highly subjective. Quoting the BPIE report again, improving acoustic comfort leads to:

  • A 0.7% increase in academic performance for every 1 dB reduction in excess noise.
  • A 0.3% improvement in performance for every 1 dB reduction in excess noise in offices.


The health crisis caused by the coronavirus is making us more aware of the indoor air quality we are exposed to on a regular basis.

But these environmental conditions not only affect the transmission of microorganisms but also have an impact on people’s performance.

Now think about what modern sensor technology can offer you, the possibilities it provides for reducing risks and increasing the sense of well-being. Ultimately, it offers an opportunity to make better decisions based on real data.

Sources consulted:

  • (1) American Society of Heating, Refrigerating and Air-Conditioning Engineers. (2011). ASHRAE Guideline 10-2011, Interactions Affecting the Achievement of Acceptable Indoor Environments. ASHRAE
  • (2) España. Real Decreto 1027/2007, de 20 de julio, por el que se aprueba el Reglamento de Instalaciones Térmicas en los Edificios. Boletín Oficial del Estado, 29 de agosto de 2007, núm. 207, pp. 35931 a 35984.
  • (3) Ahlawat, A., Wiedensohler, A. and Mishra, S.K. (2020). An Overview on the Role of Relative Humidity in Airborne Transmission of SARS-CoV-2 in Indoor Environments. Aerosol Air Qual. Res. 20: 1856–1861. doi:10.4209/aaqr.2020.06.0302
  • (4) Clements, N., Binnicker, M., & Roger, V. (2020). Indoor Environment and Viral Infections. Mayo Clinic Proceedings, 95(8), 1581-1583. doi: 10.1016/j.mayocp.2020.05.028
  • (5) Quraishi, S., Berra, L., & Nozari, A. (2020). Indoor temperature and relative humidity in hospitals: workplace considerations during the novel coronavirus pandemic. Occupational And Environmental Medicine, 77(7), 508-508. doi: 10.1136/oemed-2020-106653
  • (6) MacNaughton, P., Pegues, J., Satish, U., Santanam, S., Spengler, J., & Allen, J. (2015). Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings. International Journal Of Environmental Research And Public Health, 12(11), 14709-14722. doi: 10.3390/ijerph121114709
  • (7) Building 4 People: Quantifying the benefits of energy renovation investments in schools, offices and hospitals | BPIE – Buildings Performance Institute Europe. (2018).
  • (8) España. Real Decreto 1367/2007, de 19 de octubre, por el que se desarrolla la Ley 37/2003, de 17 de noviembre, del Ruido, en lo referente a zonificación acústica, objetivos de calidad y emisiones acústicas. Boletín Oficial del Estado, 23 de octubre de 2007, núm. 254, pp. 42952 a 42973.

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