The average adult takes over a million breaths every day [1], each of these breaths contains about 25 sextillion air molecules [2], which is such an unimaginably large number that if you line these molecules end to end, they can wrap around the earth 250 thousand times. Any of these inhaled molecules can be a part of the air pollutants responsible for 7 million deaths every year [3].

Unfortunately, most of us don’t have access to sophisticated air quality monitors to make sure that the air we’re breathing is safe. This is where low-cost air quality monitors can help. Using a large number of low-cost monitors, we can observe the spatial variation in concentrations as well as the personal exposure, and have near real-time data, which can help us drastically mitigate the health effects related to poor indoor air quality (IAQ). However, these low-cost devices aren’t without their drawbacks, the quality of these devices can sometimes be questionable, requiring careful interpretation of the measured data.

This post will introduce the different trends in low-cost devices used in air quality monitoring and answer if these devices can present a possible future in IAQ monitoring.

What is a low-cost sensor? The definition is quite relative, but monitoring devices costing a few 100s of USD with sensors costing a few 10s of USD [4] are usually considered low-cost. Alternatively, devices that can be installed in large amounts can also be considered low-cost [5]. While the definitions may slightly differ, there is a common theme of accessibility of these devices for a large number of users. This large number of deployed devices offers a large spatial distribution, which enabled programs such as the UN Environment Program [6] and the swiss federal laboratories for materials science and technology (EMPA) [7] to build an air quality monitoring network in multiple cities, gaining valuable information on the concentrations of different pollutants in the urban environment. Monitoring networks like these are leading a new paradigm shift in air quality monitoring as they can help better develop the regulatory limits for different pollutants.

Low-cost devices also offer the opportunity to crowdsource air pollution monitoring networks allowing not only large research groups, but also regular people to provide air quality data. Similar to how many apps use cellphone location data to provide accurate estimations of traffic movement in cities, these low-cost devices can provide air pollution data with high spatial and temporal distribution [8].

These crowdsourced networks of low-cost monitors can also be deployed in residential buildings, office spaces, lecture halls, and a multitude of indoor spaces in which we spend about 90% of our time [9]. Moreover, these devices can provide near real-time air quality data thanks to the many advancements in electronics and telecommunication technologies. This data can be used to improve models of pollutant emissions and personal exposure in indoor spaces, which can lead to a better understanding of the health effects these pollutants have on humans [8] and in turn help us better develop guidelines for pollutant limits for indoor spaces.

While the potential of these low-cost devices is great, the current reality is quite different. Recent studies evaluating the different low-cost devices currently deployed found that the major issue with these monitors is the reliability of the measured data [8] [10]. Many of these devices are not properly calibrated, which raises a lot of questions about the validity of the measured data. One study found that out of 895 reviewed papers using low-cost sensors to monitor IAQ, only 2 papers tested the long-term stability of these devices [10].

Even though at their current state these devices might not be providing perfectly accurate data, many leading experts in air quality monitoring believe that as long as we are aware of these limitations [11]. This can be done by take them into account these inaccuracies while doing the analysis and still be able to achieve a high degree of accuracy for the measured levels of pollutants [11]. Additionally, further advancements in the sensors’ technology coupled with an introduction of standardized calibration and testing methods can increase the level of confidence in the results obtained from these devices [8] [10]. With the global air quality monitoring market seeing steady growth, reaching an expected size of over 6 billion USD by 2022 [12], this might be the incentive needed to drive manufacturers and researchers alike to develop more reliable devices.

So, are these devices the future of IAQ monitoring? At their current state, no. However, with further advancements they have the potential to be.

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