Performance Evaluation of Atmotube Pro sensors for Air Quality Measurements

Abstract. This study presents a performance evaluation of eight Atmotube Pro sensors using US Environmental Protection Agency (US-EPA) guidelines. The Atmotube Pro sensors were collocated side-by-side with a reference-grade FIDAS monitor in an outdoor setting for a 14-week period. The result of the assessment showed the Atmotube Pro sensors had a coefficient of variation (CoV) of 23 %, 15 % and 13 % for minutes, hourly and daily PM_2.5 data averages, respectively. The PM_2.5 data was cleaned prior to analysis to improve reproducibility between units. 6 out of 8 Atmotube Pro sensor units had particularly good precision. The inter-sensor variability assessment showed two sensors with low bias and one sensor with a higher bias in comparison with the sensor average. Simple univariate analysis was sufficient to obtain good fitting quality to a FIDAS reference-grade monitor (R² > 0.7) at hourly averages although, poorer performance was observed using a higher time resolution of 15 minutes averaged PM_2.5 data (R²; 0.43–0.54). The average error bias, root mean square error (RMSE) and normalized root mean square error (NRMSE) were 4.19 µgm^-3 and 2.17 % respectively. While there were negligible influences of temperature on Atmotube Pro measured PM_2.5 values, substantial positive biases (compared to a reference instrument) occurred at relative humidity (RH) values > 80 %. The Atmotube Pro sensors correlated well with the purple air sensor (R²=0.86, RMSE=2.85 µgm^-3). In general, the Atmotube Pro sensors performed well and passed the base testing metrics as stipulated by recommended guidelines for low-cost PM_2.5 sensors.