Importance of indoor air quality in the built environment

Indoor air quality (IAQ) is an important factor in maintaining a healthy and comfortable built environment. Good IAQ can help protect the health and well-being of building occupants, improve productivity and performance, and even contribute to energy efficiency and cost savings. The major reasons why IAQ is important in the built environment include:

World Health Organization (WHO) reports that almost all of the global population (99%) breathe polluted air. Moreover, over seven million deaths yearly are due to bad air quality. Many factors contribute to poor indoor air quality. These factors involve (i) Human activities within buildings. (ii) Vapours from building and construction materials, equipment, and furniture. (iii) Outdoor pollution such as particulate matter (PM).

Among the various factors of polluted air, PM is important in posing a risk to human health. For example, PM10 (particles with a diameter of 10 microns) inhaled via the upper airways can induce cytotoxicity and inflammation. PM2.5, on the other hand, can easily penetrate the lungs and bloodstream tissues, causing respiratory and vascular diseases. Apart from PM, pollutants of major public health concern also include carbon monoxide, bio-aerosols, radon and volatile organic compounds (VOCs). However, the majority of the burden of disease associated with indoor air quality is caused by exposure to PM2.5 (Figure 1). This fine dust found indoors originates mostly from outdoor air and indoor combustion of solid fuels.

Among the various factors of polluted air, PM is important in posing a risk to human health. For example, PM10 (particles with a diameter of 10 microns) inhaled via the upper airways can induce cytotoxicity and inflammation. PM2.5, on the other hand, can easily penetrate the lungs and bloodstream tissues, causing respiratory and vascular diseases. Apart from PM, pollutants of major public health concern also include carbon monoxide, bio-aerosols, radon and volatile organic compounds (VOCs). However, the majority of the burden of disease associated with indoor air quality is caused by exposure to PM2.5 (Figure 1). This fine dust found indoors originates mostly from outdoor air and indoor combustion of solid fuels.

Figure 1. The burden of disease associated with the key pollutants of indoor air quality. Source: Promoting actions for healthy indoor air (IAIAQ)

Traditional indoor air quality parameters

The main parameters of indoor air quality include particulate matter (PM2.5 and PM10, diameters 2.5 and 10 microns, respectively), carbon dioxide (CO₂), volatile organic compounds (VOCs), humidity, and temperature. Multiple health organizations such as the World Health Organization (WHO), European Environment Agency (EPA) and others provide guidelines to what safe and acceptable levels of those parameters are in various indoor air spaces as exposure to those air pollutants can have a detrimental effect on our health and productivity.

PM2.5 is a fine dust that can travel deeply into the respiratory tract. Which can cause short-term health effects such as eye, nose, throat, and lung irritation, coughing, sneezing, runny nose, and shortness of breath. Extensive evaluation of research regarding PM2.5 made WHO issue new guidelines with stricter levels of PM2.5 as a new target (annual mean of 5 μg/m³ and 24-h of 15 μg/m³). Nevertheless, studies show that indoor PM2.5 concentrations in office settings in developing and developed countries already exceed the previous (2005 version) limits and the latest WHO guidelines (2021 version) are challenging to meet. Yet, there is enough evidence linking exposure to particulate air pollution and worsening cognitive functions, which will be discussed later in this report in detail (Zhou et al., 2023).

Humidity can have both positive and negative effects on human health and well-being, depending on its level and other factors such as temperature. On the one hand, low humidity levels can cause dry skin, dry eyes, and respiratory problems such as coughing and congestion. The negative effects also include damaging electronic devices because of static electricity due to dry air. On the other hand, high humidity levels can also have negative effects on human health. When the air is humid, it can feel sticky and uncomfortable, making it harder for the body to cool itself through sweating. High humidity levels can also contribute to the growth of mould, bacteria, and other allergens, which can trigger respiratory problems and other health issues. Therefore, it is recommended to keep moderate relative humidity (RH) levels between 40 – 60% (Figure 2).

One of the easiest and most common methods of minimizing static electricity is to increase the relative humidity level. Electrostatic charges do not dissipate through moist air, but through a moisture film that is absorbed on the charged surfaces. This moisture film decreases the surface resistance and causes static charges to be drained. This effect is most pronounced at RH above 30-35% and it also corresponds to a decrease in ozone production (a by-product of electrostatic discharge).

Humidification systems are used for office environments to reduce employees' susceptibility to colds and viral infections.

The principle on which this conventional and energy-consuming technology is based is called competitive exclusion. Removing any one of the 3 factors: living space, moisture, and nutrition. To create an unfavourable environment in which particular life forms do not thrive or even proliferate (grow).

Figure 2. Optimum relative humidity range for minimizing adverse health effects. Source: Arundel et al., 1986

The importance of our Indoor Environmental Quality (IEQ) will be a trending topic for the years to come. The recent crisis showed us how vulnerable we are inside our offices and buildings. One of the biggest shifts to make it in the way we see the outdoors Instead of something to keep out at all costs, we have started to understand how interaction with nature can be beneficial for our lives.“Air” a prime element for life and vital for well-being provides an answer to the relationship between the microbial and chemical components of an indoor space.

Apart from the abiotic parameters, biotic pollutants such as microorganisms (bacteria, viruses, and mould) can also cause multiple adverse health effects including allergic reactions, respiratory problems, infections, and toxic reactions. Notably, the load and variability of microorganisms indoors are strictly related to other IAQ parameters, which are discussed below, and the key to healthy microbial composition of indoor air lies in its balance and diversity.

Indoor microbiome and microbial air quality

Although, from ancient times, humans have adapted to rich microbial exposures starting from their early life, and changes in these exposures in modern urbanized environments may drive the epidemic increases in asthma and allergies (Rook & Lowry, 2022). This issue is also postulated by the hygiene hypothesis; the rising prevalence of allergic diseases is causally related to reduced exposure to environmental microbes and harmless infections, with parallel increasing economic wealth (Jatzlauk et al., 2017). Indeed, exposure to microbes is essential for immune system development and training and has long been associated with decreased prevalence of atopic diseases (Pfefferle et al., 2021)

The interplay between indoor air quality and microbiome

Indoor air quality can have a significant impact on the indoor microbiome. Studies show that indoor air quality parameters have a direct effect on the concentration, diversity and even virulence of microorganisms (Purves et al., 2022). Various studies, especially the ones conducted in the hospital context link indoor air quality parameters such as temperature, relative humidity, CO₂, and particulate matter to pathogen survival or mitigation of pathogen spread (Leung & Chan, 2006). It has also been reported that the relative abundances of pathogenic bacteria were highest in heavily and moderately polluted air respectively (Liu et al., 2018) as depicted in Figure 3.

In general, overall ventilation performance can have a significant role in shaping the indoor microbiome. Fresh air from the outside can introduce new microorganisms to the indoor environment, which can help diversify the microbiome and reduce the concentration of potentially harmful microorganisms. Also, too high humidity levels (above 60%) can promote the growth of mould and other fungi, which can contribute to a less diverse and potentially harmful indoor microbiome. Finally, some microorganisms can increase indoor air quality by lowering volatile organic compounds (VOCs) concentrations (Malhautier et al., 2005) or contributing to the decomposition of small airborne particles such as PM2.5 (Gao et al., 2016).

Overall, maintaining a healthy indoor microbiome is important for promoting good IAQ and protecting the health of building occupants. This can be achieved through a combination of proper ventilation, humidity control, appropriate cleaning practices, the use of building materials that support a diverse and healthy indoor microbiome or the implementation of technologies that introduce beneficial microorganisms designed to improve microbial diversity and enhance the IAQ.

Figure 3. Illustration summarizing the relationship between the concentration of air pollution and pathogenic bacteria. The more polluted the air with PM2.5 and PM10 the more pathogenic bacteria were found. Modified version from (Liu et al., 2018).

Air pollution: the invisible killer of productivity and well-being

Typically, or more historically, the main reasons for ventilation were to create a healthy indoor environment. However, an emerging number of studies show that poor air quality has a negative impact not only on our health but also on cognitive functions and productivity.

Centre for Indoor Environment and Energy (ICIEE) at the Technical University of Denmark (DTU) published a series of 10 experiments that successfully quantified the effects of indoor environmental factors on performance, and in particular, the effects of poor indoor air quality. The authors reported that poor indoor air quality reduced the performance of office workers by 6–9% and that there is a relationship between the number of complaints about indoor air quality and the measured decrement in performance (D.P. Wyon, 2004).

A recent study by Harvard T.H. Chan School of Public Health confirmed that the adverse effects of poor indoor air quality such as delayed response times and ability to focus also apply to the working-age population (1-year study with 302 office workers in six countries). In particular, higher PM2.5 and CO₂ levels were associated with slower response times and reduced accuracy (Cedeño Laurent et al., 2021).

Poor indoor air quality also affects strategic decision making as it was demonstrated by Künn et al., 2023 in the analysis that linked readings of air-quality monitors inside the tournament room to the quality of 30,000 moves. The authors found that poor indoor air quality hinders players’ decision-making. In particular, an increase in the indoor concentration PM2.5 by 10 µg/m³ led to a 26,3% higher probability of a player’s erroneous move. Moreover, the analysis showed that time pressure combined with poor indoor air quality magnifies those adverse effects on the decision making which highlight the costs of poor air quality for highly skilled professionals faced with strategic decisions under time pressure (Künn et al., 2023)

From a building owner or a property management perspective, the scientific evidence implies that even small improvements from relatively low baseline levels of air pollution exposure (e.g., like in high-performance office buildings) may have substantial economy-wide implications.

The economic impact of poor indoor air quality

Poor indoor air quality is not only a health concern. Since the Covid-19 pandemic, there has been a strong paradigm shift in the way we percept air quality, especially indoors where we spend most of our time. The growing amount of evidence about the link between the quality of indoor air and productivity and health opens a debate about how this “invisible” factor such as air affects the economy on the global as well as entrepreneurial level. The Promoting Action for Healthy Indoor Air Project (IAIAQ) estimated that in the EU every year two million of healthy life is lost due to poor indoor air quality (Jantunen et al., 2011).

Traditionally economic debate around indoor air quality focuses on calculating the costs of providing ventilation such as costs of designing, purchasing, and installing the ventilation system (costs of the building) and later on the costs of running the system (operating costs) including electricity to run the fans and energy to condition the outdoor air. In this case, the economic calculation is straight-forward with all the usual economic assumptions. However, when it comes to the far larger economic impact related to productivity and health loss by the building users, the numbers get exigent.

The urgent need for a Biodiverse Indoor environment

Supporting evidence

Publications endorsing the vision and inextricable necessity of indoor microbiome, which in turn, boosts your health.