Our results suggest that mixing times in phenolic SOA generated from NO 3 may often be > 1 h in the planetary boundary layer and free troposphere. These results have possible implications for predicting the size and mass of biomass burning phenolic SOA and the long-range transport of pollutants within biomass burning phenolic SOA. Additional research is needed to determine if other types of phenolic SOA formed by NO 3 reactions have viscosities and mixing times similar to guaiacol-NO 3 SOA.