In-line identification of aerosol particles

A method for in-line identifying a chemical composition of particulate matter in an aerosol, the method comprising:

• receiving an aerosol stream of the aerosol, having an initial particulate matter concentration, at an impactor inlet of an impactor;
• diverting the aerosol stream to an outlet stream at a first impactor outlet of the impactor and to a sensing stream at a second impactor outlet of the impactor,
• wherein the impactor provides:
• the outlet stream with a decreased particulate matter concentration compared to the initial particulate matter concentration, and
• the sensing stream with 100 to 100,000 time increased particulate matter concentration compared to the initial particulate matter concentration, and
• tunable particulate matter concentration;
• and
• wherein separation of the particulate matter at the impactor is based on differences in inertia of various particles comprised in the aerosol;
• directing the sensing stream via a fluid connection from the second impactor outlet into a flow cell inlet of an optical flow cell, wherein the sensing stream is guided via an elongate hollow wave guide of the optical flow cell to a flow cell outlet of the optical flow cell;
• directing a beam of light into a light inlet of the optical flow cell,
• wherein light of the beam of light travels through the elongate hollow wave guide to a light outlet of the optical flow cell,
• wherein the optical flow cell forms both a gas flow path for the sensing stream along the elongate hollow wave guide between the flow cell inlet and flow cell outlet, and an optical path for the light along the elongate hollow wave guide between the light inlet and the light outlet, and
• wherein the gas flow path and the optical path at least in part follow a common trajectory in the elongate hollow wave guide of the optical flow cell to allow light travelling along the common trajectory to interact with particulate matter of the tunable particulate matter concentration comprised in the sensing stream for identification of the chemical composition of the particulate matter in the aerosol;
• and
• identifying the chemical composition of the particulate matter based on an absorption at one or more wavelengths of the light by the increased particulate matter concentration in the sensing stream in the common trajectory of the elongate hollow wave guide.