Spectropolarimetry is a powerful technique for remote sensing of the environment. It enables the retrieval of particle shape and size distributions in air and water to an extent that traditional spectroscopy cannot. SPEX is an instrument concept for spectropolarimetry through spectral modulation, providing snapshot, and hence accurate, hyperspectral intensity and degree and angle of linear polarization. Successful SPEX instruments have included groundSPEX and SPEX airborne, which both measure aerosol optical thickness with high precision, and soon SPEXone, which will fly on PACE. Here, we present a low-cost variant for consumer cameras, iSPEX 2, with universal smartphone support. Smartphones enable citizen science measurements which are significantly more scaleable, in space and time, than professional instruments. Universal smartphone support is achieved through a modular hardware design and SPECTACLE data processing. iSPEX 2 will be manufactured through injection molding and 3D printing. A smartphone app for data acquisition and processing is in active development. Production, calibration, and validation will commence in the summer of 2020. Scientific applications will include citizen science measurements of aerosol optical thickness and surface water reflectance, as well as low-cost laboratory and portable spectroscopy.algorithm for c and a from multi-angular DoLP data. 9 Finally, spectropolarimetry of vegetation probes its physical characteristics, such as leaf orientation, and provides reflectance distribution functions, which are crucial for improving the accuracy of air-or space-based aerosol retrieval algorithms. 10Combining spectral and polarimetric measurements can be done in multiple ways. 11 First, regular spectroradiometers can be fitted with rotating polarizing filters, as was done in the aforementioned studies of water and vegetation. 9, 10 A second method is 'channeled' spectropolarimetry, where polarization information is encoded into the spectrum itself. One method for channeled linear spectropolarimetry is SPEX, 12 the basis for SPEXone. 6 In SPEX, incoming light is modulated with a sine wave with an amplitude and phase depending on the DoLP and the Angle of Linear Polarization (AoLP), respectively. 12 This is further explained in Sec. 2.2.The SPEX technique has been applied successfully in two high-end field-going instruments measuring aerosol optical thickness (AOT, sometimes termed aerosol optical depth, AOD), namely groundSPEX 13 and SPEX airborne. 14 GroundSPEX is a ground-based instrument based on a dual-channel fiber-optic spectrometer with SPEX optics on a moving mount, allowing sequential measurements at multiple angles. Its AOT measurements are well-correlated (Pearson r = 0.932) 13 with data from AERONET, the global network of photometers observing the solar almucantar and principal plane. 15 SPEX airborne, as the name implies, is an airborne instrument, simultaneously observing at nine fixed viewing angles. A 2017 campaign on a NASA ER-2 high-altitude aircraft demonstrated excellent...