Blended optical methods. You can find various proprietary optical smoke measurement gadgets such as the 'nephelometer' or even the 'aethalometer' which use many different optical strategies, which include more than one wavelength of sunshine, inside an individual instrument and utilize an algorithm to present a good estimate of smoke. https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/