10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Ageing of Sea Spray Aerosols: Effects on Hygroscopicity and Cloud Droplet Activation
BERNADETTE ROSATI, Sigurd Christiansen, Robert Lange, Andreas Massling, Merete Bilde, Aarhus University
Abstract Number: 91 Working Group: Aerosol Physics
Abstract Sea spray aerosols (SSA) are continuously emitted into the Earth’s atmosphere and play a significant role in the planetary energy budget, by interacting directly with solar radiation and by affecting the formation and lifetime of clouds. This has a major effect on climate since 70% of the planet is covered by the ocean, which thereby is the largest single source of aerosol mass in the atmosphere (e.g. de Leeuw et al. 2011). The atmospheric lifetime of SSA varies from seconds to weeks. During this time, SSA is exposed to oxidants, condensable vapors, light and changing conditions of relative humidity and temperature, which induce so-called ageing effects. Hence, the properties of SSA may be significantly altered, which leads to changes in their role for climate.
The hygroscopic behavior of SSA, at sub- saturated conditions of relative humidities (RH), influences the type and magnitude of the aerosol-radiation interactions because the optical properties of the aerosol particles change due to water uptake. The hygroscopicity may also affect the particles’ efficiency to act as cloud condensation nuclei (CCN) at supersaturated conditions. Commonly, the hygroscopicity and CCN-activity of SSA is assumed to be comparable to that of sodium chloride (NaCl; Lewis and Schwartz, 2004), which is the major component of SSA particles overall (Lewis and Schwartz, 2004). Previous laboratory studies have investigated reactions of aqueous NaCl with ozone and the presence of UV-light, hereby mimicking ageing conditions occurring in the marine boundary layer (Knipping et al., 2000, Laskin et al., 2003). These experiments demonstrated changes in the chemical and physical properties of the particles and hence the authors hypothesize a possible effect on the hygroscopic and cloud activation potential.
In this study, we examine the hygroscopic and cloud forming potential of SSA after atmospheric ageing processes. To simulate different atmospheric conditions, we use the constrained conditions of the Aarhus University Research on Aerosol (AURA) smog chamber (Kristensen et al., 2017), which provides a temperature regulation between 257 and 299 K. In our experiments, the chemical composition of SSA is first simplified by using pure NaCl particles generated with a TSI atomizer. In a second step, another generation technique, i.e. a sea spray chamber, and more complex mixtures of inorganic salts are used. Hygroscopicity is measured with a humidified tandem differential mobility analyzer (Brechtel) while a cloud condensation nucleus counter (DMT) is used to investigate the cloud droplet activation of the fresh and aged particles. Additionally, the particle number size distribution is monitored with a scanning mobility particle sizer (SMPS; TSI) and an optical particle sizer (OPS; TSI). We will present first results of ageing experiments, where NaCl undergoes oxidation due to gases and UV-radiation as present in the atmosphere. We will show that only deliquesced NaCl particles lead to chemical reactions influencing the hygroscopic and CCN-activity and that the results strongly depend on the pre-treatment of the aerosol particles.
[1] de Leeuw, G., E. L Andreas, M. D. Anguelova, C. W. Fairall, E. R. Lewis, C. O'Dowd, M. Schulz, and S. E. Schwartz (2011), Rev. Geophys., 49, RG2001. [2] Knipping, E. M., M. J. Lakin, K. L. Foster, P. Jungwirth, D. J. Tobias, R. B. Gerber, D. Dabdub, B. J. Finlayson-Pitts, (2000). Science, 14: 301-306. [3] Kristensen, K., Jensen, L.N., Glasius, M., Bilde, M. (2017). Environ. Sci.: Processes Impacts, 19:1220-1234. [4] Laskin, A, Gaspar, D.J., Wang, W.H., Hunt, S.W., Cowin, J.P., Colson, S.D., Finlayson-Pitts, B.J. (2003), Science, 301: 340-344. [5] Lewis, E. R. and Schwartz, S. E. (2004). Sea Salt Aerosol Production, American Geophysical Union.