A direct method to quantify methanol-soluble organic carbon for brown carbon absorption studies

The current research provides a newly developed method to quantify methanol-soluble organic carbon (MeS_OC) in aerosol samples. This analytical procedure allows an accurate separation of MeS-OC component, which is critical for the calculation of mass absorption efficiency (MAE) of ambient Brown Carbon (BrC) and consequently its climate relevant potential. The method includes extraction, filtering and condensation stages, leading to the preparation of a highly concentrated product in which MeS-OC can be precisely quantified by a Sunset Carbon Analyzer in a single analysis step. This method can be applied on aerosol collected using either high or low volume samplers, since a relatively small filter area is required for the determination. Furthermore, it eliminates any misestimation of the MeS-OC mass that may appear in other reported techniques that don't seem to include the precise separation of methanol-soluble fraction in their quantification process. • The mass quantification of methanol-soluble organic carbon is essential, contributing up to 50% to the absorptivity of organic aerosol (BrC) at shorter wavelengths. • The method provides a direct measurement of methanol-soluble aerosol components, resolving any potential uncertainties of previously applied methods. • The adoption of this direct quantification approach leads to a rationalization of past MAE estimates for BrC with implications for radiative transfer models.