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Abstract. Biomass burning emits vapors and aerosols into the atmosphere thatcan rapidly evolve as smoke plumes travel downwind and dilute, affectingclimate- and health-relevant properties of the smoke. To date, theory hasbeen unable to explain observed variability in smoke evolution. Here, we useobservational data from the Biomass BurningObservation Project (BBOP) field campaign and show that initial smokeorganic aerosol mass concentrations can help predict changes in smokeaerosol aging markers, number concentration, and number mean diameterbetween 40–262 nm. Because initial field measurements of plumes aregenerally >10 min downwind, smaller plumes will have alreadyundergone substantial dilution relative to larger plumes and have lowerconcentrations of smoke species at these observations closest to the fire.The extent to which dilution has occurred prior to the first observation isnot a directly measurable quantity. We show that initial observed plumeconcentrations can serve as a rough indicator of the extent of dilutionprior to the first measurement, which impacts photochemistry, aerosolevaporation, and coagulation. Cores of plumes have higher concentrationsthan edges. By segregating the observed plumes into cores and edges, we findevidence that particle aging, evaporation, and coagulation occurred beforethe first measurement. We further find that on the plume edges, the organicaerosol is more oxygenated, while a marker for primary biomass burningaerosol emissions has decreased in relative abundance compared to the plumecores. Finally, we attempt to decouple the roles of the initialconcentrations and physical age since emission by performing multivariatelinear regression of various aerosol properties (composition, size) on thesetwo factors.