We next assessed the response of bandpass filters C310 (310 ± 5 nm) and C350 (350 ± 25 nm) to establish a numerical detection model for SCs present in e-liquid, similar to the principle of our previous detection method. Our previous work shows that the ratio of these spectral regions can be modelled to establish numerical model for alarm thresholding. A total of 60 e-cigarettes were artificially actuated and measured with the EDD, 39 containing unaltered e-liquid and 21 containing 1.5 mg/mL SC (MDMB-4en-PINACA x15, MDMB-CHMICA x6) e-liquid. Figure shows the averaged response of PDs C310 and C350 for both SC and unaltered e-liquids. When SCs are present the average response of C350 rises from 61 to 481 arbitrary units, this increase is visualized spectroscopically in Figures and, where contributions from SC emission alone are responsible for increased signal magnitude in the spectral region of C350 (325-375 nm). Inversely, presence of SCs in e-liquid reduces the average magnitude of the C310 response, dropping from 261 to 206 when SCs are present. This change is visualized in figures 4B and S2C and arises through a decrease in reflected light from loaded filters. We suggest this is predominantly caused by the relative increase in absorption from ~280-320 nm when SC are present in e-liquid (Figure ).