Heterogeneous nucleation drives particle size segregation in sequential ozone and nitrate radical oxidation of catechol

Gas-to-particle conversion is generally thought to occur on a continuum between equilibrium-driven partitioning of semivolatile molecules to the pre-existing mass size distribution and kinetic-driven condensation of low volatility molecules to the pre-existing surface area size distribution.

However, we offer experimental evidence in contrast to this framework. When catechol is sequentially oxidized by O-3 and NO3 in the presence of (NH4)(2)SO4 seed particles with a single size mode, we observe a bimodal organic aerosol mass size distribution with two size modes of distinct chemical composition with nitrocatechol from NO3 oxidation preferentially condensing onto the large end of the pre-existing size distribution (similar to 750 nm).