Influence of surfactants on growth of individual aqueous coarse mode aerosol particles

Abstract

Understanding the links between aerosol and cloud and radiative properties remains a large uncertainty in predicting Earth's changing energy budget. Surfactants are observed in ambient atmospheric aerosol particles, and their effect on cloud droplet growth is a mechanism that was, until recently, neglected in model calculations of particle activation and droplet growth. In this study, coarse mode aqueous aerosol particles were created containing the surfactant Igepal CA-630 and NaCl. The evaporation and condensation of these individual aqueous particles were investigated using an aerosol optical trap combined with Raman spectroscopy. For a relative humidity (RH) change from 70% to 80%, droplets containing both Igepal and NaCl at atmospheric concentrations exhibited on average more than 4% larger changes in droplet radii, compared to droplets containing NaCl only. This indicates enhanced water uptake in the presence of surfactants, but this result is unexpected based on the standard calculation of the effect of surfactants, using surface tension reduction and/or hygroscopicity changes, for particles of this size. One implication of these results is that in periods with increasing RH, surfactant-containing aqueous particles may grow larger than similarly sized aqueous NaCl particles without surfactants, thus shifting atmospheric particle size distributions, influencing particle growth, and affecting aerosol loading, visibility, and radiative forcing. EDITOR Ilona Riipinen

Effects of surface tension time-evolution for CCN activation of a complex organic surfactant

“…18,20 Here, we calculate Köhler curves for dry particles composed of NAFA and NaCl of size 50-150 nm in 10 nm increments and Fig. 3, together with the corresponding ternary ts to eqn (5). Plots of measurement data and ternary ts for the remaining time steps t ¼ 0, 400, 600, and 800 s are presented in the ESI † as well as the residuals for all the ts.…”

“…Plots of measurement data and ternary ts for the remaining time steps t ¼ 0, 400, 600, and 800 s are presented in the ESI † as well as the residuals for all the ts. Ternary surface tension parameters resulting from the tting procedure described for eqn (5) are given in Table 1 for ts corresponding to all times steps. The surface tensions corresponding to time step t ¼ 0 s were previously presented by Kristensen et al, 21 who also presented raw time-evolving surface tension data for a single NAFA : NaCl mass mixing ratio of 80 : 20 at two single concentration points.…”

“…In submicron activating droplets, the bulk/surface partitioning introduces a complex relation between droplet growth and surface tension equilibrium. Essentially, the bulk/surface partitioning must be evaluated for each droplet size and composition before the surface tension can be found from eqn (5). This moves the droplet in composition space, possibly on both axes simultaneously, and the effect on evaluated droplet surface tension can be dramatic.…”

“…It is well-known that surface tension is an important parameter in the activation of aerosol particles into cloud droplets and that surface-active organic species can contribute to the depression of surface tension compared to that of pure water. [1][2][3][4][5][6] It is also well-established that surface tension equilibrium can take a long time to be achieved and may involve several dynamic stages, such as reorganization and phase transitions in the surface layer following the initial surface adsorption. [7][8][9][10][11] Such dynamic effects are currently not accounted for in atmospheric cloud and droplet models.…”

Linking marine phytoplankton emissions, meteorological processes and downwind particle properties with FLEXPART

“…Several other studies have also shown that ocean productivity and biomass abundance relate to the spatial and temporal variability in MBL particle and cloud droplet concentrations (McCoy et al, 2015;Meskhidze and Nenes, 2010;Vallina et al, 2006). While sulfate is more hygroscopic than organic aerosol mass, the latter still contributes to the particle size (which lowers the Kelvin effect) and may decrease the surface tension (Frossard et al, 2018;Ovadnevaite et al, 2017). Organics are likely to contribute to CCN concentrations considering organics often account for a significant fraction of marine Aitken-and accumulation-mode particle mass.…”