Fundamental understanding of low-cost sensor response

Air quality data is increasingly being obtained from devices that contain low-cost optical sensors (LCOSs) such as Plantower PMS5003 and Sensirion SPS30. The LCOSs measure particle optical scattering response and convert the data to real-time integrated mass concentration such as PM1, PM2.5, and PM10. Accurate ambient measurements with these sensors often require on-site calibration, typically by co-location with reference-grade sensors. The use of correlation-based correction is necessary because of the black box nature of the sensors, leaving us with limited fundamental understanding of their performance. Here, we demonstrate that the working of LCOS devices can be explained using a technique we label as focused light scattering (FLS). In this technique, particles intersect a laser profile with a very tightly focused spot size (order of tens of micrometers) and a Rayleigh length much smaller than the cross-section of the flow. In FLS, particles are illuminated with varying intensity of light on either side of the focal spot, and a photodiode captures single-particle scattering response over a wide range of scattering angles that vary with particle size. For the LCOSs studied here, the scattering angle range was ∼16 to 164 degrees for 10 µm particles and ∼39 to 143 degrees for 0.3 µm. We demonstrate that the FLS theoretical response accurately captures the experimentally determined size-dependent detection efficiency of both the LCOS devices tested. This theoretical approach could help improve the design of FLS-based units and potentially provide theory-based corrections of field data when particle properties are known.Copyright © 2026 American Association for Aerosol Research