Understanding the links between aerosol and cloud and radiative properties remains a large uncertainty in predicting Earth’s changing energy budget. Surface active compounds, surfactants, have been 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 our work, model coarse mode aqueous aerosol particles are created containing a representative surfactant and salt. The evaporation and condensation of these aqueous particles are investigated using an aerosol optical trap combined with Raman spectroscopy. This instrument allows us to measure the properties of individual aerosol particles, which we can compare to growth factors and water uptake of bulk aerosol particles measured by a Humidified Tandem Differential Mobility Analyzer (HTDMA). Additionally, the aerosol optical trap allows the surfactants and compounds within the particles to come to equilibrium before quantifying. For a small change in relative humidity (RH) change, model aqueous particles containing both the surfactant Igepal and NaCl at atmospheric concentrations exhibited on average larger changes in droplet radii, compared to aqueous particles 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.

Measuring the influence of surfactants on the growth of individual aqueous coarse mode aerosol particles

2019 Spring National Meeting

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