Blended optical strategies. You'll find various proprietary optical smoke measurement gadgets including the 'nephelometer' or even the 'aethalometer' which use quite a few different optical approaches, including more than one wavelength of sunshine, inside a single instrument and apply an algorithm to offer a very good estimate of smoke. https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/