To model hydrated aerosols, atmospheric chemistry models use the volume weighted mixing rule to predict the complex refractive index (RI) of aerosols when they interact with high RH areas, and, in general, assume homogeneous mixing. The validity of these assumptions is explored through a closure study between hygroscopic growth and optical properties of scattering and absorbing aerosols.  The extinction coefficient and growth factor of humidified aerosols was measured for size-selected aerosols of AS, peat, nigrosine, and a mixture of AS and nigrosine. The ratio of the humidified extinction coefficients to the dry is explored. The measured fRHext is compared to theoretical calculations based on Mie theory, and using the measured growth factors and assuming homogeneous mixing the expected RIs using the volume weighted mixing rule are compared to the RIs derived from the extinction measurements. Moreover, the differences between assuming a core-shell structure or a homogeneous mixing of the substances is examined.

Interaction of absorbing aerosols with high relative humidity

243rd National Meeting (2012)

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