Challenges in characterizing air quality with low-cost sensors

Air pollution is a great health concern for the governments, but also for the population, especially in urban environments. Particulate matter (PM) levels are regulated by European standards and are therefore continuously monitored by official measurement networks with precision instruments that are regularly calibrated. Although citizens often have access to open data, these networks are not usually dense. During the last years, low-cost sensors for measuring air quality have become popular, allowing the establishment of citizen science networks in which the population takes an active attitude in capturing measurements.

In the framework of the European project I-CHANGE, the Barcelona Living Lab on Extreme Events  has used eight Smart Citizen Kits of the company Fablab, with different low-cost sensors including the Plantower PMS5003 that estimates the concentration of PM10, PM2.5, PM1 (referring the number to the maximum radius of the measured particles, in micrometers). The sensors were initially installed alongside an official instrument GRIMM EDM 180 providing PM10 and PM2.5 for 3 weeks, to intercompare the ability of these devices to measure PM. These sensors together with low-cost weather stations have been distributed in different schools in Barcelona, in the context of a citizen science campaign with a double objective: to analyze the use of this type of sensors to have more detailed information on pollution in areas of Barcelona with different characteristics and to raise awareness in the school community and promote changes in habits in response to the European Green Pact.

The results of the intercomparison show that the instruments have a good performance for PM2.5 estimation, with an average determination coefficient (R²) of 0.84 with the official instrument, when comparing 10-minute averages. On the other hand, the instruments have worse quality in the estimation of PM10 (R²=0.64) as could be seen during the Saharan dust intrusion that affected the city. The laser-based measurement system does not allow a good characterization of coarse particles. Despite these differences with the official data, the agreement among low-cost sensors was good (R² higher than 0.95 for PM10 and PM2.5), so the variations detected when displayed separately can be relied upon. During the time they have been located in schools, starting in January 2023 the longest series, they have allowed to monitor PM concentrations in different areas of the city. The comparison of PM evolution between official instruments and low-cost sensors during high concentration events have shown that the latter can have an informative and pedagogical role in raising public awareness on air quality.

This study is supported by the project “Individual Change of HAbits Needed for Green European transition (I-CHANGE)”. I-CHANGE has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement 101037193.