Part 1: The logic and science behind Indoor Air Quality monitoring & management

Today more than half of the earth’s population lives in cities, and spend most of their time indoors. Therefore, we need the indoor spaces we inhabit to be healthy and comfortable environments that support our wellbeing. To contribute to that support and wellbeing, human psychology looks to the built environment for protection; the buildings where we work and live need to be safe havens.

Indoor environmental quality (IEQ) is one of the core aspects of ensuring that buildings are healthy, safe and comfortable for human occupation. IEQ includes indoor air quality (IAQ), as well as the physical and psychological aspects of life indoors. These include lighting, visual quality, acoustics, thermal comfort, etc.

IAQ is one of the strongest predictors of workplace health, as well as workforce performance. Poor IAQ has been linked to both physical and psychological health symptoms. Additionally, poor IAQ is known to have a significant impact on cognitive functioning and is one of the leading causes of distractions and decreased productivity.

Historically the focus for improvement has been predominantly on the comfort metrics, specifically temperature. Measuring the other comfort and indoor air quality metrics have been surprisingly limited.

Similarly, the impact of indoor environmental quality on psychological wellbeing and performance of employees in the workplace has been underestimated and consequently received limited attention.

A Harvard Business Review Survey was conducted to understand what employees want most from their workspaces. Surprisingly, it was found that employees want the basics first: better air quality, access to natural light, and the ability to personalize their workspace. Air quality specifically was the biggest influencer of employee performance, happiness, and wellbeing, and was mentioned as the most important factor by 58% of the respondents.

1. Measuring building conditions and evaluating building health

The adage, ‘you can’t manage what you can’t measure’ couldn’t ring more true in the case of indoor air quality. If you do not have any idea what your building is doing, then how do you know if there is a problem or not? Furthermore, how can you measure any success if you implement remediation plans? It has become critical for buildings to have a baseline from which facilities managers can begin the process of indoor air cleaning measures.

As a first step, building managers should collect real-time data on the important environmental and air quality metrics and continuously monitor fluctuations in their buildings. The upshot? Having robust data allows for an understanding of the building’s health and behaviour, and also then provides for immediate responses and adjustments; whether it be to a building’s mechanical system or to suggest changes in occupant behaviour.

Furthermore, we must think about preventative, instead of reactive, care. Not all buildings are alike, solutions might be nuanced, and need to be evaluated on a building-by-building basis. This underscores the importance of being informed by accurate real-time and historical data for every building and workspace.

The technology exists that can measure the following important indoor environmental metrics that matter when it comes to maintaining healthy indoor spaces:

  • Temperature

  • Humidity

  • CO2

  • TVOCs

  • PM Contaminants

  • Sound

  • Light

1.1. Temperature

1.1.1. Effects on occupants

Conventional wisdom says that finding the ideal office temperature is important to worker productivity: Thermal comfort is the source of one of the most frequent complaints in office environments. In periodic facility satisfaction surveys, being hot and being cold have consistently been the top two complaints about office environments. We can therefore see a difference of just a few degrees can have a significant impact on how focused and engaged employees are.

Guidline Summary:

Cold <15

Cool 15 - 19

Temperate 19 - 25

Warm 25 - 28

Hot > 28

1.1.2. Management difficulties

Of course, individual preferences vary, for instance, generally, women prefer a slightly higher temperature. This makes it difficult to please everyone, especially when you have complex buildings or office layouts to contend with.

In addition to an ambient temperature, the humidity of an environment has a big influence on how people experience it. The apparent temperature, or “feels like” temperature, is a way to express what the temperature seems like to a person. High humidity levels could feel warmer and low humidity could feel cooler.

“The term “thermal comfort” refers to a condition that is governed by many environmental and human factors; in other words, physiological, physical, and sociopsychological factors.” - Mujeebu (2020)

1.1.3. Recommended levels

Available research found that keeping the office temperature between 21 and 23 degrees Celsius would be best for the majority of workers in a “typical” office environment. The U.S. Occupational Safety and Health Administration (OSHA) doesn’t mandate employers to maintain specific temperatures in the workplace, but it recommends that employers keep the thermostat between 20 and 24 degrees Celsius.

1.2. Humidity

1.2.1. Effects on occupants

The relative humidity level plays a significant role in determining the quality of indoor environments – impacting both the health and comfort of occupants.

Guideline Summary:

Safest range:

40% - 60%

According to the American Industrial Hygiene Association (AIHA), uncontrolled humidity levels are one of the main factors for poor indoor air quality (IAQ). Overly low or high relative humidity can introduce a range of respiratory issues, irritated skin and eyes, reduced mental focus, and general discomfort – resulting in productivity loss and health issues.

When the air is too muggy it can make occupants feel irritable and psychologically inhibited. By contrast, the air that is too dry can make employees susceptible to pathogens by drying out their mucous membranes. It can also make them susceptible to nosebleeds and chronic respiratory or sinus issues.

Moreover, very high indoor humidity is associated with increased growth of micro-organisms such as mould and infectious bacteria (Institute of Medicine, 2004). At the same time, viruses survive much longer when humidity levels are low, therefore airborne pathogens are effectively given free rein in drier conditions. This increases the risk of illness flashing through the building. The greatest benefit that you may obtain from dialling in the perfect humidity levels is a decrease in sickness.

Did you know? Carpets are roughly 10% more humid than the space it is in. It acts as a sink for pollutants as well. Maintaining and cleaning carpets is therefore a vital aspect of ensuring a safer IEQ.

1.2.3. Recommended levels

The U.S. Occupational Safety and Health Administration recommend that offices maintain a relative humidity level between 40% and 60%.

1.3. CO2

1.3.1. CO2 basics

Carbon dioxide is a natural component of air, and in indoor environments, the source is usually the building’s occupants - the people. Humans exhale carbon dioxide, therefore the levels of CO2 correlate with human metabolic activity. Indoor CO2 levels are a clear indicator of the adequacy of outdoor air ventilation relative to indoor occupant density.

Guideline Summary:

Keep average levels below 800ppm.

The (acute) maximum should not surpass the 1500 ppm mark.

1.3.2. Effects on occupants

It is well documented that carbon dioxide levels have a significant impact on the cognitive functioning and productivity of workers. CO2 at levels that are unusually high indoors may cause occupants to grow drowsy, to get headaches, or to function at lower activity levels.

According to a new study from Harvard, researchers found that cognitive performance scores for the participants who worked in the green+ environments were, on average, double those of participants who worked in conventional environments.

Measuring nine cognitive function domains researchers found that the largest improvements occurred in crucial areas such as responding to a crisis or developing strategy.

1.3.3. Recommended levels

The normal concentration of CO2 in outdoor air is between 300 and 400 ppm. Indoor levels are typically quite a bit higher, due primarily to the concentration of exhaled air from the people in the building. CO2 levels in office buildings typically range between 350 to 2500 ppm. It has been demonstrated that levels above 1000 ppm tend to result in health complaints, and a general guideline is that levels should be below 800 ppm to ensure everyone’s comfort and ability to function optimally.

1.4. TVOC

1.4.1. What are TVOCs?

Volatile organic compounds, (VOCs) are organic chemical compounds whose composition makes it possible for them to evaporate under normal indoor atmospheric conditions. VOCs are a nearly unavoidable byproduct of our daily lives and are exceedingly common in our indoor environments, as it is released by many of the products surrounding us day-to-day, including some cleaning solutions.

Due to the wide range of organic chemical compounds that fall under the umbrella of VOCs, the term Total Volatile Organic Compounds or TVOCs is used to simplify reporting when these compounds are present in ambient air.

Guideline Summary:

Average levels should be < 200 ppb

Direct exposure:

Short-term (hours) exposure should not exceed 40ppb

Long-term (weeks) exposure should not exceed 100ppb

1.4.2. Effects on occupants

The health effects of exposure to VOCs range from sensory irritation, headaches and nausea at low/medium levels of exposure, to frank toxic effects at high exposure levels. The latter may include serious health issues including neurotoxic, organotoxic and carcinogenic effects.

In addition to the obvious health risks, studies have found that relatively high levels of VOC exposure also have a direct impact on cognitive performance and employee productivity. One study by the Harvard School of Public Health even suggested a 13% decrease in productivity for every 500μg/m3 increase in VOC.

1.4.3. Recommended levels

Acceptable levels of VOCs range between 0.3 to 0.5 mg/m3. When levels increase to 1 mg/m3 or more, it is concerning and should be addressed. A suggested threshold for TVOC in indoor environments is 200 PPB (Parts Per Billion).

1.5. Particulate matter (PM)

1.5.1. What is particulate matter?

Particulate Matter (PM) – also known as atmospheric aerosol particles, atmospheric particulate matter, particulates, or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The term aerosol commonly refers to the particulate/air mixture, as opposed to the particulate matter alone. Sources of particulate matter can be natural or anthropogenic.

Guideline Summary:


10 μg/m3 (annual mean)

25 μg/m3 (24-hour mean)


20 μg/m3 (annual mean)

50 μg/m3 (24-hour mean)

Particulate matter is the most harmful form of air pollution due to its ability to penetrate deep into the lungs, bloodstreams and brain, causing severe health problems. The effects of inhaling particulate matter have been widely studied in humans and animals and include asthma, lung cancer, respiratory diseases, cardiovascular disease, premature delivery, birth defects, low birth weight, and premature death.

Types of atmospheric particles include :

  • Suspended particulate matter with a diameter bigger than 10 μm;

  • Inhalable coarse particles (PM10) with a diameter of 10 μm or less;

  • Fine particles (PM2.5) with a diameter of 2.5 μm or less;

  • Ultrafine particles (PM 0.1) with a diameter of 0.1 μm or less.

1.5.2. Mass vs Count

PM is measured in count and by mass. The two measurements are used to gauge which type of particles and prevalent and how much.

The particles pass a series of consecutive filters to be measured, hence the larger PM size measurement contains the measurements of the smaller sizes as well. The result of the above PM measurement would be:

With these values, the following can be determined:

1.5.3. Effects on occupants

PM2.5 is of particular concern as it can penetrate to alveoli, the gas exchange area in the lungs, and hence the circulatory system.

Because of the small size, ultrafine particulate matter (PM0.1) can enter deep into our lungs and may pass through cell membranes and migrate into other organs, including the brain, and do all manner of harm.

In 2013, a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg/m3 in PM10, the lung cancer rate rose 22%. The smaller PM2.5 were particularly deadly, with a 36% increase in lung cancer per 10 μg/m3 as it can penetrate deeper into the lungs. Worldwide exposure to PM2.5 contributed to 4.1 million deaths from heart disease and stroke, lung cancer, chronic lung disease, and respiratory infections in 2016. Overall, ambient particulate matter ranks as the sixth leading risk factor for premature deaths globally.

Other than the impact on the global population from a health perspective, the current calculations of the societal cost of air pollution may be substantially underestimated. A growing body of evidence in health sciences suggests that exposure to poor air quality may also have harmful immediate and lasting impacts on the human brain, ultimately lowering individuals’ cognitive abilities (Underwood, 2017). Exposure to air pollution alone has been shown to have severe health consequences which may translate into adverse effects on human capital formation and labour market outcomes in the short and long run (Graff Zivin and Neidell, 2013, 2018). These physiological effects on human cognition may have severe consequences for individual performance in complex cognitive tasks.

A recent study by Künn et al at Maastricht University studied the impact of indoor air quality on the cognitive performance of individuals using data from official chess tournaments. The results show that poor indoor air quality hampers cognitive performance significantly. The study found that an increase in the indoor concentration of fine particulate matter (PM2.5) by 10 μg/m3 increases a player’s probability of making an erroneous move by 26.3%. The impact increases in both magnitude and statistical significance with rising time pressure. The study found clear evidence suggesting a short-term and transitory effect of fine particulate matter on cognition.

Quantifying the benefits of improving air quality has to expand beyond major health impacts that result in hospitalizations or deaths, and additionally take into account more subtle effects on labour productivity and human capital accumulation.

1.5.4. Recommended levels

WHO Guidelines for the annual and 24-hour mean levels for PM concentration respectively are:


10 μg/m3 (annual mean)

25 μg/m3 (24-hour mean)


20 μg/m3 (annual mean)

50 μg/m3 (24-hour mean)

1.6. Light

1.6.1. Effects on occupants

Human comfort issues have always been the focus of green buildings. Especially, lighting (visual sense), acoustics (auditory sense), and temperature and humidity (thermal sense) have led to major discussions in providing human comfort in green buildings. Lighting in our living and workplaces is critically important for our ability to accomplish tasks efficiently and safely. Also, proper light levels prevent eye strain, which allows us to work comfortably for longer periods.

Guideline Summary:

300–500 lux

1.6.2. Recommended levels

Visual comfort strategies for workplace health mainly address lighting for visual acuity, glare control, and quality of lighting. To provide sufficient lighting level, 300 lux is recommended for general areas and 300–500 lux for computer workstations.

1.7. Sound

1.7.1. Ambient environment

Auditory comfort has been a major discussion in the modern workplace. Open-plan offices have become a prevalent office type in the contemporary workplace due to efficient real estate management. The importance of open environments has been emphasized to facilitate interaction and collaboration in the innovation economy.

Guideline Summary:

Safe area:

30 - 65dB

1.7.2. Effects on occupants

However, the downside of an open environment is excessive noise that causes annoyance, stress, and physical fatigue, not to mention the loss of concentration and productivity.

High-noise environments are proven to be detrimental to a person’s mental health and stress levels. In particular, loud sounds and prolonged exposure to noise can trigger psychological responses in the body, including spikes in a person’s heart rate and blood pressure. In addition to causing mental health and mood issues, prolonged noise exposure can have a direct impact on a person’s ability to do their job well. In a study by Joshua Dean at MIT, he found that noise can have a significant impact on productivity by impeding cognitive function in employees.

Did you know? The biggest culprit in noise pollution is road traffic, and the leading cause of permanent hearing loss due to expose to too high sound levels are personal audio devices, like headphones.

1.7.3. Recommended levels

In an office building, the recommended sound levels are between 30 and 65dB, and for open-plan offices, the recommended levels are 40-45dB.

Click here to read Part 2 of our research.


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


3. Steffen Künn SEPTEMBER (2019) Maastricht University, Indoor Air Quality and Cognitive Performance.

4. Setti, L., Passarini, F., de Gennaro, G., Di Gilio, A., Palmisani, J., Buono, P., Fornari, G., Perrone, M.G., Piazzalunga, A., Barbieri, P., et al. (2020). Evaluation of the Potential Relationship between Particulate Matter (PM) Pollution and COVID-19 Infection Spread in Italy.

5. 3. Bontempi, E. (2020). First data analysis about possible COVID-19 virus airborne diffusion due to air particulate matter (PM): The case of Lombardy (Italy). Environ. Res. 186, 109639.

6. 7. Maitre, A., Bonneterre, V., Huillard, L., Sabatier, P., and de Gaudemaris, R. (2006). Impact of urban atmospheric pollution on coronary disease.

7. Tang, J.W. (2009) The effect of environmental parameters on the survival of airborne infectious agents.

8. Tang, J.W et al. (2014) Absence of detectable inuenza RNA transmitted via aerosol during various human respiratory activities.

9. Setti etall, (2020), University of Bologna, Italy. Evaluation of the potential relationship between Particulate Matter (PM) pollution and COVID-19 infection spread in Italy.

10. Verreault, D., Moineau, S. and Duchaine, C. (2008) Methods for sampling of airborne viruses Gerone, et al (1966) Assessment of experimental and natural viral aerosols.

11. Ciencewicki J. et al., (2007). Air Pollution and Respiratory Viral Infection.

12. Sedlmaier N. et al., (2009). Generation of avian influenza virus (AIV) contaminated fine particulate matter (PM2.5): Genome and infectivity detection and calculation of immission.

13. Wu, X , Harvard (2020). Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study.

14. 8. Conticini, E., Frediani, B., and Caro, D. (2020). Can atmospheric pollution be considered a co-factor in extremely high level of SARSCoV-2 lethality in Northern Italy.

15. Travaglio, (2020). Links between air pollution and COVID-19 in England.

16. Yaron Ogen, (2020), Martin Luther University of Halle-Wittenberg in Germany. Assessing nitrogen dioxide (NO2) levels as a contributing factor to coronavirus (COVID-19) fatality 17. Cole et all, 2020, Environmental and Resource Economics. Air Pollution Exposure and Covid-19 in Dutch Municipalities.

18. Ward, August 18, (2020) the University of Sydney. Low humidity increases COVID-19 risk.

19. WHO Guidelines for Indoor Air Quality: Dampness and Mould. Geneva: World Health Organization; (2009). WHO (2014) Infection Prevention and Control of Epidemic‐and Pandemic‐Prone Acute Respiratory Infections in Health Care. Geneva, Switzerland: World Health Organization.

20. World Health Organisation, Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations, Scientific brief.

21. Muhammad Abdul Mujeebu (January 9th 2019). Introductory Chapter: Indoor Environmental Quality, Indoor Environmental Quality, Muhammad Abdul Mujeebu, IntechOpen, DOI: 10.5772/intechopen.83612. Available from:

Recent Posts

See All