Field Calibration and Performance of Low-Cost Sensors in Kathmandu Valley for Ambient PM2.5 Monitoring

Low-cost sensors offer a cost-effective alternative for air quality monitoring but require field validation to ensure accuracy and reliability in local environment. This study proposes a field calibration approach for TSI BlueSky sensors and evaluates their performance in measuring PM₂.₅ under diverse environmental conditions in Kathmandu, Nepal, using the reference-grade monitor, GRIMM EDM 180. Before collocating with the reference monitor, the sensors were inter-compared to assess their individual responses to ambient PM_2.5 concentrations. The sensors demonstrated strong consistency, with coefficients of variation ranging between 2% and 15%, indicating high precision and reliability. Harmonization of the sensors using median values enhanced the sensors’ performance coherence. The sensors displayed strong correlations with the GRIMM EDM 180 with correlation coefficient ranging from 0.85 to 0.97. The coefficient of determination (R²) ranged from 0.73 to 0.95, with values exceeding 0.90 for 70% of measurements indicating strong agreement between the two instruments. The sensors tended to underestimate PM₂.₅ levels during dry months. Relative humidity had a negligible influence on performance during specific environmental conditions, suggesting that humidity corrections may not be universally necessary. Analysis of particulate matter size distributions revealed greater underestimation when coarse particles dominated, particularly during pollution episodes, whereas accuracy improved with higher fine particle fractions. These findings highlight the importance of considering seasonal variations and aerosol composition when calibrating low-cost sensors to enhance data reliability. Incorporating season-specific calibration can significantly improve accuracy under varying environmental conditions. Properly calibrated and harmonized, TSI BlueSky sensors have strong potential for reliable PM₂.₅ monitoring, offering valuable insights to support air quality management and policy interventions in resource-limited settings.