Photochemistry of iron(III) complexes plays an important role in aerosol aging, especially in the lower troposphere. Ensuing radical chemistry leads to decarboxylation, and the production of peroxides, and oxygenated volatile compounds, resulting in particle mass loss due to release of the volatile products to the gas phase. We investigated kinetic transport limitations due to high particle viscosity under low relative humidity conditions. For quantification a numerical model was developed.