A versitile system for the multi-angular measurement of the aerosol scattering matrix and aerosol aerodynamic size.

The proposed Multi-angle Phase Matrix Polarimeter (MP2) will be the first field-worthy and aircraft-adaptable instrument for in situ measurements of the aerosol scattering phase matrix that allow for characterization of aerosol physical and optical properties. These measurements can lead to inference of aerosol type with a temporal resolution of minutes. The MP2 follows from a history of polar nephelometers that illuminate suspended aerosol particles in a chamber and then measure the scattered light as a function of angle. With the MP2 we intend to modulate polarization at the source and then measure not the intensity but the polarization signal at the detector. This can provide measures of six elements of the scattering phase matrix, at multiple scattering angles. Previous polar nephelometer technology has stopped halfway, modulating polarization at the light source, but then only measuring intensity at the detector. Thus, existing technology has achieved measurements of only two phase matrix elements (P11 and P12). The six phase matrix elements will contain unprecedented information about aerosol properties that can be retrieved from inversion software. Furthermore, the MP2 is designed to be modular with possible connection to an inlet with an aerodynamic sizer. This allows size selection, such as PM2.5, before characterization of the phase matrix. Multiple stacked MP2s, allow for phase matrix measurements for multiple particle size categories. There are two possible options to achieve the MP2. Option (a) uses multiple light sources (LEDs) and a single polarimeter detector. Option (b) uses a single light source (multi-wavelength laser) and multiple fiber detectors. Each option can achieve the technical objectives. The technical proposed work is to build a tabletop demonstration of both options and then evaluate the best option for Phase II. Options will be evaluated as to technical feasibility, sensitivity, portability, durability and marketability.

The MP2 will support NASA’s future polarimeter missions: PACE, MAIA and ACCP. These satellite polarimeters will revolutionize aerosol remote sensing from space. As space sensors attain greater capability, suborbital options must evolve to keep up. Otherwise, you have a situation where the “ground truth” is less believable than the satellite retrieval. The MP2 offers NASA the opportunity for cal/val activity for polarimeters and aerosols that will exceed any of NASA’s current plans.

Global interest in aerosol research in air quality and climate is in a growth phase. The MP2 with its aerodynamic sizing options fits well with the air quality monitoring of PM2.5 and need for particle characterization and source apportionment, internationally. Collocating MP2 at 100s of AERONET stations links column retrievals with particle properties at “nose level”.

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