Evaluating the Performance of Low-cost PM Sensors over Multiple COALESCE Network Sites

Air quality is a global concern, with particulate matter receiving considerable attention due to its impact on human health and climate change. Recent advances in low-cost sensors allow their deployment in large number to measure spatio-temporal and real-time air quality data. Low-cost sensors need careful evaluation with both regulatory approved methods and other data sets to understand their efficacy. In this work, PM concentrations measured by deploying low-cost sensors at four regional sites are evaluated through comparison with satellite-based model MERRA-2 and the SASS reference instrument. Daily PM_(2.5) mass concentration variation was analyzed at four regional sites of India from January 2020 to July 2020, including pre-lockdown and six different lockdown periods. Higher PM_(2.5) concentration was observed at Rohtak (119 μg m^(-3)) compared to Mahabaleshwar (33 μg m^(-3)), Bhopal (45 μg m^(-3)) and Kashmir sites during the pre-lock down period. During the lockdown period, the PM_(2.5) mass concentration was reduced significantly compared to the pre-lockdown period at every location, although the PM_(2.5) concentration was different at each location. The air quality trend was quite similar in both the measurements, however, MERRA-2 reconstructed PM_(2.5) was significantly lower in the pre-lockdown period compared to the lockdown periods. Significant differences were observed between low-cost sensor measurements and MERRA-2 reanalysis data. These are attributed to the MERRA-2 modelling analysis that measures less PM_(2.5) concentration as compared to ground-based measurements, whereas low-cost sensor are ground-based measurements but needs corrections as it is subject to the calibration dependencies and biases.