Solving the air quality monitoring dilemma.

The British Institute of Air Quality Management (IAQM) recently organised a webinar in which Bruno Beloff from the company South Coast Science examined the thorny issue of whether low-cost air quality monitors are able to offer data of sufficient accuracy and reliability to be comparable with reference grade monitors.

Bruno explained that his company was established in 2016 to offer a common digital front-end for electrochemical sensors, together with an open data management framework. Early field work was conducted in cooperation with academia, research organisations and the United Nations, and Bruno emphasised the importance of this field work in the development of monitors that are suitable for real-world applications.

Low-cost air quality monitors employ electrochemical sensors for gas measurements and optical particle counters for the measurement of particulate fractions. These sensors are provided by Alphasense, which in the case of the gas sensors, have demonstrated an ability to measure concentrations to within +/- 5 ppb. “The Alphasense sensors are ubiquitous in the market,” explains South Coast Science Commercial Director David Johnson. “Without reliable sensors, it would be impossible to develop effective algorithms, so it was important for us to partner with Alphasense from the outset.”

Alphasense sensors are highly repeatable in the laboratory, but the outputs from electrochemical sensors are affected by a number of environmental factors, such as temperature and humidity, and in some cases interfering gases. Working in different locations around the world, South Coast Science therefore employed machine learning techniques to improve and speed up the process of algorithm development. As a consequence, the company was able to develop monitors that were able to apply these refined algorithms in real-time and within the monitors themselves; delivering data with extremely low levels of interference or noise.

There are no formally recognised performance standards for low-cost air quality monitors, so it is incumbent on instrument developers to conduct trials in a variety of different environments to validate the claims made on websites and in brochures. South Coast Science has therefore conducted over three years of co-location studies with reference air quality monitoring stations provided by Ricardo. This work has demonstrated a high degree of correlation with data from the reference stations (see graph). In addition, there is an MCERTS performance standard for indicative ambient particulate monitors, and Bruno is hopefully that Praxis will be the first low-cost monitor to achieve the required level of performance without the need for a heated sample inlet (to remove moisture).

South Coast Science launched the ‘Praxis’ air quality monitor in 2017, and Bruno explained that the open data management framework provided by these monitors means that users, if they wish, can use both raw and corrected data in order to evaluate the algorithms.

The Praxis/Urban offers sensing for gases (CO, H2S, NO, NO2, O3, SO2, CO2, VOCs) and particulates (PM1, PM2.5 and PM10). The device supports multiple analysis techniques including any sampling rate and real-time data access. Consistent device function is possible within a broad range of climatic conditions. This includes continuous operation for up to two hours in the event of external power loss, as well as a 24 month Warranty.

One of Bruno’s first presentation slides showed a small Praxis device fitted to the top of a large reference air quality monitoring station. This image, Bruno explained, clearly demonstrated the main advantages of low-cost monitors, because it showed how easy it is to install them almost anywhere. This flexibility means that low-cost monitors can be installed at pollution hot-spots, alongside developments or where remediation measures need to be assessed.

Summarising Bruno says: “Our development work has achieved remarkable results in that we have managed to create monitors which provide data that correlates very well with reference monitors, but at a fraction of the cost. Nevertheless, we do not believe that low-cost monitors should replace reference monitors; we believe that they should supplement them, by enabling the creation of monitoring networks that measure air quality in the locations that matter the most.”

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