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. This two-part study explores hyperspectral (300–700 nm) aerosol optical measurements obtained from in situ sampling methods employed duringthe May–June 2016 Korea–United States Ocean Color (KORUS-OC) cruise conducted in concert with the broader air quality campaign (KORUS-AQ). Part 1focused on the hyperspectral measurement of extinction coefficients (σext) using the recently developed in situ Spectral AerosolExtinction (SpEx) instrument and showed that second-order polynomials provided a better fit to the measured spectra than power law fits. Twodimensional mapping of the second-order polynomial coefficients (a1, a2) was used to explore the information content of the spectra. Part 2expands on that work by applying a similar analytical approach to filter-based measurements of aerosol hyperspectral total absorption(σabs) and soluble absorption from filters extracted with either deionized water (σDI-abs) or methanol(σMeOH-abs). As was found for σext, second-order polynomials provided a better fit to all three absorption spectrasets. Averaging the measured σext from Part 1 over the filter sampling intervals in this work, hyperspectral single-scatteringalbedo (ω) was calculated. Water-soluble aerosol composition from the DI extracts was used to examine relationships with the variousmeasured optical properties. In particular, both σDI-abs(365 nm) and σMeOH-abs(365 nm) were foundto be best correlated with oxalate (C2O42-), but elevated soluble absorption was found from two chemically and optically distinctpopulations of aerosols. The more photochemically aged aerosols of those two groups exhibited partial spectra (i.e., the longer wavelengths of thespectral range were below detection) while the less-aged aerosol of the other group exhibited complete spectra across the wavelength range. Thechromophores of these groups may have derived from different sources and/or atmospheric processes, such that photochemical age may have been onlyone factor contributing to the differences in the observed spectra. The differences in the spectral properties of these groups was evident in(a1, a2) maps. The results of the two-dimensional mapping shown in Parts 1 and 2 suggest that this spectral characterization may offer newmethods to relate in situ aerosol optical properties to their chemical and microphysical characteristics. However, a key finding of this work isthat mathematical functions (whether power laws or second-order polynomials) extrapolated from a few wavelengths or a subrange of wavelengths fail toreproduce the measured spectra over the full 300–700 nm wavelength range. Further, the σabs and ω spectraexhibited distinctive spectral features across the UV and visible wavelength range that simple functions and extrapolations cannot reproduce. Theseresults show that in situ hyperspectral measurements provide valuable new data that can be probed for additional information relating in situaerosol optical properties to the underlying physicochemical properties of ambient aerosols. It is anticipated that future studies examining in situaerosol hyperspectral properties will not only improve our ability to use optical data to characterize aerosol physicochemical properties, but thatsuch in situ tools will be needed to validate hyperspectral remote sensors planned for space-based observing platforms.

atmospheric measurement techniques

New in situ aerosol hyperspectral optical measurements over 300–700 nm – Part 2: Extinction, total absorption, water- and methanol-soluble absorption observed during the KORUS-OC cruise