Polarity and oxidation level of visible absorbers in model organic aerosol

How to parametrize the absorptivity of organic aerosols in atmospheric radiative models remains uncertain. Here we report that the λ = 400 nm absorbers in model aerosol mixtures elute as weakly polar species in reversed-phase chromatography. Typical among them, the m/z = 269 (C12H13O7−, O/C = 0.58) isomers detected by mass spectrometry possess CO groups linked by CC bridges. More polar species, such as the m/z = 289 (C11H13O9−, O/C = 0.82) polyacids, are instead colorless. On this basis we argue that visible absorptivity, which develops from extended conjugation among chromophores, may not increase monotonically with oxidation level.