Blended optical methods. You will discover various proprietary optical smoke measurement devices like the 'nephelometer' or the 'aethalometer' which use a number of different optical approaches, including more than one wavelength of light, inside of just one instrument and use an algorithm to offer a fantastic estimate of smoke. https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/