Interactive comment on “Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities” by M. Song et al

The authors have measured relative humidity-dependent viscosity of toluene SOA after a series of publications on viscosity measurements of a-pinene and isoprene SOA. This group is currently one of the only groups that can achieve such challenging measurements by combining two different unique experimental methods of a bead-mobility technique and a poke-flow technique. Based on viscosity measurements and RH observations in major urban cities in the world, they estimated whether anthropogenic SOA particles in these cities would be well-mixed or not. The experiments seem to