Predicting Real Refractive Index of Organic Aerosols From Elemental Composition

Abstract

Abstract Accurate estimates of aerosol refractive index (RI) are critical for modeling aerosol‐radiation interaction, yet this information is limited for ambient organic aerosols, leading to large uncertainties in estimating aerosol radiative effects. We present a semi‐empirical model that predicts the real RI n of organic aerosol material from its widely measured oxygen‐to‐carbon (O:C) and hydrogen‐to‐carbon (H:C) elemental ratios. The model was based on the theoretical framework of Lorenz‐Lorentz equation and trained with n‐values at 589 nm (n589nm) of 160 pure compounds. The predictions can be expanded to predict n‐values in a wide spectrum between 300 and 1,200 nm. The model was validated with newly measured and literature datasets of n‐values for laboratory secondary organic aerosol (SOA) materials. Uncertainties of n589nm predictions for all SOA samples are within ±5%. The model suggests that n589nm‐values of organic aerosols may vary within a relatively small range for typical O:C and H:C values observed in the atmosphere.

Keywords

• atmospheric organic aerosols
• refractive index prediction
• elemental composition
• optical properties
• ultraviolet and visible wavelength
• aerosol radiative forcing