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Formaldehyde levels (log-scale) from e-cigarettes with different coil structure (top- and bottom coil) and power outputs (low and high levels determined by lower and higher power outputs [5 watts for top coil and 18 watts for bottom coil] used in the literatures). Red dots indicate our results, and black dots are the results obtained from literatures [4,13,14,15,19,22,45,46,47,48,49]. Formaldehyde levels in cigarette smoke from literatures [50,51,52] are shown for comparison purpose.
