A device for quantifying absolute amounts of at least one of ingredients of a plume of a vehicle, comprising: (a) a light source for emitting a beam of light through the plume to a surface on which the light is scattered; (b) a light sensitive detector capable of acquiring images composed of pixels for acquiring an image of the plume containing information of absorption of the scattered light scattered from the surface, wherein absorption of the scattered light being caused by light absorbing molecules of the at least one of ingredients of the plume; (c) an optical collecting means for forming said image by directing a portion of the scattered light onto the detector; and (d) a processor for processing the acquired image to determine an absolute amount of the at least one of ingredients of the plume, characterised in that the processor is configured to perform further the functions of: (i) choosing a plurality of pixels from the acquired image, said plurality of pixels depicting a section crossing the plume transversely to a direction of travel of the vehicle and representing a detected area A m of said section, each pixel being assigned a pixel area A i that corresponds to a respective part of the detected area A m depicted by the respective pixel; (ii) characterizing an absorption rate I/I 0 of light of each chosen pixel from the acquired image; (iii) calculating an optical mass μ of each pixel from the characterized absorption rate I/I 0 of the pixel by the Beer's Law: μ=-ln(I/I 0)/κ(v), with κ(ν) denoting a monochromatic absorption cross section corresponding to the spectrum of the received light for the at least one of ingredients of the plume; (iv) multiplying the optical mass μ of each pixel with the respective pixel area A l to obtain the number of light absorbing molecules of the at least one of ingredients of the plume in each pixel; and (v) summing the number of light absorbing molecules of each pixel to obtain the total number of light absorbing molecutes of the at least one of ingredients of the plume in said section crossing the plume depicted by the plurality of pixels. (a) a light source for emitting a beam of light through the plume to a surface on which the light is scattered; (b) a light sensitive detector capable of acquiring images composed of pixels for acquiring an image of the plume containing information of absorption of the scattered light scattered from the surface, wherein absorption of the scattered light being caused by light absorbing molecules of the at least one of ingredients of the plume; (c) an optical collecting means for forming said image by directing a portion of the scattered light onto the detector; and (d) a processor for processing the acquired image to determine an absolute amount of the at least one of ingredients of the plume, characterised in that the processor is configured to perform further the functions of: (i) choosing a plurality of pixels from the acquired image, said plurality of pixels depicting a section crossing the plume transversely to a direction of travel of the vehicle and representing a detected area A m of said section, each pixel being assigned a pixel area A i that corresponds to a respective part of the detected area A m depicted by the respective pixel; (ii) characterizing an absorption rate I/I 0 of light of each chosen pixel from the acquired image; (iii) calculating an optical mass μ of each pixel from the characterized absorption rate I/I 0 of the pixel by the Beer's Law: μ=-ln(I/I 0)/κ(v), with κ(ν) denoting a monochromatic absorption cross section corresponding to the spectrum of the received light for the at least one of ingredients of the plume; (iv) multiplying the optical mass μ of each pixel with the respective pixel area A l to obtain the number of light absorbing molecules of the at least one of ingredients of the plume in each pixel; and (v) summing the number of light absorbing molecules of each pixel to obtain the total number of light absorbing molecutes of the at least one of ingredients of the plume in said section crossing the plume depicted by the plurality of pixels. (i) choosing a plurality of pixels from the acquired image, said plurality of pixels depicting a section crossing the plume transversely to a direction of travel of the vehicle and representing a detected area A m of said section, each pixel being assigned a pixel area A i that corresponds to a respective part of the detected area A m depicted by the respective pixel; (ii) characterizing an absorption rate I/I 0 of light of each chosen pixel from the acquired image; (iii) calculating an optical mass μ of each pixel from the characterized absorption rate I/I 0 of the pixel by the Beer's Law: μ=-ln(I/I 0)/κ(v), with κ(ν) denoting a monochromatic absorption cross section corresponding to the spectrum of the received light for the at least one of ingredients of the plume; (iv) multiplying the optical mass μ of each pixel with the respective pixel area A l to obtain the number of light absorbing molecules of the at least one of ingredients of the plume in each pixel; and (v) summing the number of light absorbing molecules of each pixel to obtain the total number of light absorbing molecutes of the at least one of ingredients of the plume in said section crossing the plume depicted by the plurality of pixels.