Dilution impacts on smoke aging: Evidence in BBOP data

Abstract. Biomass burning emits vapors and aerosols into the atmosphere that can rapidly evolve as smoke plumes travel downwind and dilute, affecting climate- and health-relevant properties of the smoke. To date, theory has been unable to explain variability in smoke evolution. Here, we use observational data from the BBOP field campaign and show that initial smoke concentrations can help predict changes in smoke aerosol aging markers, number, and diameter. Because initial field measurements of plumes are generally > 10 minutes downwind, smaller plumes will have already undergone substantial dilution relative to larger plumes. However, the extent to which dilution has occurred prior to the first observation is not a measurable quantity. Hence, initial observed concentrations can serve as an indicator of dilution, which impacts photochemistry and aerosol evaporation. Cores of plumes have higher concentrations than edges. By segregating the observed plumes into cores and edges, we infer that particle aging, evaporation, and coagulation occurred before the first measurement, and we find that edges generally undergo higher increases in oxidation tracers, more decreases in semivolatile compounds, and less coagulation than the cores.