Fig. 1: Distribution of sensor sensitivity across sensor batches.

a–d NO2, NO, CO, and O3 sensitivity variations across diverse calibration samples, sorted by calibration R2 values to visualize the relationship between sensitivity and R2 distribution. The color indicates the R2 values between the calibrated sensors and reference data. e–h present boxplots showing the distribution of the corresponding sensor sensitivities, where the central red line represents the median, the box indicates the interquartile range (IQR) from the first quartile to the third quartile, and the black whiskers extend to the values within 1.5 times the IQR. The blue whiskers represent the overall minimum and maximum values.