The impact of atmospheric oxidation on hygroscopicity and cloud droplet activation of inorganic sea spray aerosol

Abstract

Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.

Secondary aerosol formation from dimethyl sulfide – improved mechanistic understanding based on smog chamber experiments and modelling

“…In the model, we considered the gradual compaction and dilution of the chamber volume due to the instrument sampling (see description in the Supplement Sect. S2.1) (Rosati et al, 2021a). The inflow of air from outside the chamber is a likely source for the particle contamination (nitrate and organics) observed with the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) (Rosati et al, 2021b).…”

Hygroscopicity and CCN potential of DMS-derived aerosol particles

“…Our observed trend is in line with the predicted temperature dependence obtained with the Arrhenius expression used in the Master Chemical Mechanism version 3.3.1 (MCMv3.3.1) andHoffmann et al (2016), delineating slower reaction rates at colder temperatures. The decay of the concentration of DMS over time for similar experiments at 293 and 273 K, dry and humid conditions, was formerly presented inRosati et al (2021b) and Wollesen deJonge et al (2021). Wollesen deJonge et al (2021) found good agreement between measured and modelled decay rates using the ADCHAM box model.Nucleation and growth rates are known to be inherently dependent on temperature and RH(Seinfeld and Pandis, 2016).…”

“…Berg et al, 1998;Nilsson et al, 2001;Lewis and Schwartz, 2004;Swietlicki et al, 2008;Modini et al, 2010;Fuentes et al, 2011) and ability to serve as CCN (e.g. Covert et al, 1998;Ovadnevaite et al, 2011;King et al, 2012;Prather et al, 2013;Collins et al, 2013Collins et al, , 2016Nguyen et al, 2017;Fossum et al, 2018;Rosati et al, 2021b) of marine aerosols and, in particular, sea spray aerosols have been studied intensively. Few studies have addressed the water uptake behaviour of secondary DMS-derived aerosols.…”

Chemical Composition of an Ultrafine Sea Spray Aerosol during the Sea Spray Chemistry and Particle Evolution Experiment

“…8 The composition of SSA, especially the sea salt component, impacts its ability to serve as cloud droplets due to the hygroscopicity of these chemical components. 9 It is important to understand the processes that control SSA production and composition because of its significant role in Earth's radiative budget. 10 SSA is produced via physical ejection of sea spray droplets produced by bubble-bursting.…”

“…Atmospheric aerosol plays a critical role in Earth’s radiative budget but remains the single largest source of uncertainty in models estimating potential changes in radiative forcing. , The atmospheric impacts of particles are dependent upon multiple factors including the composition, size, and number concentration, which can all affect their ability to serve as cloud condensation nuclei (CCNs). − Sea spray aerosols (SSA) are an important contributor to the total aerosol mass globally. , SSA can be activated into cloud droplets, which have been shown to potentially change the albedo of marine boundary layer clouds by as much as 30% . The composition of SSA, especially the sea salt component, impacts its ability to serve as cloud droplets due to the hygroscopicity of these chemical components . It is important to understand the processes that control SSA production and composition because of its significant role in Earth’s radiative budget …”