The high viscosities of the SOA should similarly be considered when analyzing TD measurements. When converting TD measurements to volatilities, researchers have often assumed that the SOA particles are well mixed, implying their viscosity is low and not a kinetic barrier to evaporation. For most TD measurements, particle diameters are on the order of 200 nm. We calculated lower limits to viscosities and mixing times within 200 nm catechol SOA as a function of temperature (Fig. ). However, we are not able to determine if 200 nm catechol SOA particles will be well mixed in TD measurements when heated to mild temperatures since the calculations were lower limits. For some TD measurements, sub-micrometer SOA particles are first collected on a surface using an impactor. If particle collection times are long and particle mass loadings are high, sub-micrometer SOA particles will coagulate on the surface and form particles with dimensions greater than 1 µm. If the particle dimensions reach ~200 µm, the SOA particles will not be well mixed in TD measurements when heated to mild temperatures based on our calculations (Fig. ).