Blended optical methods. You can find various proprietary optical smoke measurement units like the 'nephelometer' or the 'aethalometer' which use a number of unique optical strategies, which include more than one wavelength of light, inside an individual instrument and implement an algorithm to present a fantastic estimate of smoke. https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/