Aerosol size distribution changes in FIREX-AQ biomass burning plumes: the impact of plume concentration on coagulation and OA condensation/evaporation

Abstract. The evolution of organic aerosol (OA) and size distributions within smoke plumes is uncertain due to the variability in rates coagulation OA condensation/evaporation between different at locations a single plume. We use aircraft data from FIREX-AQ campaign evaluate differences evolving distributions, OA, oxygen carbon ratios (O:C) during first several hours aging as function concentration. observations show that median particle diameter increases faster higher initial concentration (>1000 µg m−3), with growth over 100 nm 8 h – despite generally having net decrease enhancement than lower (<100 which had OA. Observations O:C suggest evaporation and/or secondary formation was greater less concentrated prior measurement (5–57 min after emission). simulate changes dilution adjust for based on observed found explains majority growth, evaporation/condensation relatively minor impact. mixing core edges plume occurred timescales hours, slow enough maintain edge but too fast ignore role most our cases.