Abstract
Abstract. Condensation of carboxylic acids on mineral particles leads to coatings and impacts the particles' potential to act as cloud condensation nuclei (CCN). To determine how the CCN activity of mineral particles is impacted by carboxylic acid coatings, the CCN activities of CaCO3 particles and CaCO3 particles with oleic acid and malonic acid coatings were compared in this study. The results revealed that small amounts of oleic acid coating (volume fraction (vf) ≤4.3 %) decreased the CCN activity of CaCO3 particles, while more oleic acid coating (vf ≥16 %) increased the CCN activity of CaCO3 particles. This phenomenon has not been reported before. In contrast, the CCN activity of CaCO3 particles coated with malonic acid increased with the thickness of the malonic acid coating (vf =0.4–40 %). Even the smallest amounts of malonic acid coating (vf =0.4 %) significantly enhanced the CCN activity of CaCO3 particles from κ=0.0028±0.0001 to κ=0.0123±0.0005. This indicates that a small amount of water-soluble organic acid coating may significantly enhance the CCN activity of mineral particles. The presence of water vapor during the coating process with malonic acid additionally increased the CCN activity of the coated CaCO3 particles, probably because more CaCO3 reacts with malonic acid when sufficient water is available.
Highlights
Atmospheric aerosols serve as cloud condensation nuclei (CCN) and change the radiative properties and lifetime of clouds, affecting the Earth’s climate indirectly (Liu and Wang, 2010; Gantt et al, 2012; Penner et al, 2004; Haywood and Boucher, 2000)
The increase in κ by 0.0008 at 80 ◦C was smaller than the differences of reported κ values for CaCO3 aerosol in various studies and much smaller than the changes of κ values measured in this study when the CaCO3 aerosol particles were coated by malonic acid (MA) or oleic acid (OA)
The Dcrit at different supersaturations (SScrit) for the CaCO3 aerosol and for the CaCO3 aerosol passed through a blank coating device at heating temperatures of 60 and 80 ◦C are shown in Fig. 5
Summary
Atmospheric aerosols serve as cloud condensation nuclei (CCN) and change the radiative properties (cloud albedo effect) and lifetime (cloud lifetime effect) of clouds, affecting the Earth’s climate indirectly (Liu and Wang, 2010; Gantt et al, 2012; Penner et al, 2004; Haywood and Boucher, 2000). Russell et al (2002) found that carbonyls (R(C=O)R), alkanes, and R(C=O)OH are present in individual mineral (and sea salt) aerosol particles, with enhanced concentration of R(C=O)OH They found that Ca2+, CO23−, R(C=O)OH, and R(C=O)R coexisted in some individual mineral aerosol particles with a strong correlation between CO23− and R(C=O)OH. These particles could be formed by CaCO3 particles (partly) coated with organic film. A possible explanation for such observations could be that when more water is condensed onto mineral particles at higher ambient RH, the adsorbed carboxylic acids are ionized in the aqueous environment and react with mineral particles forming organic acid salts. It has been reported that DCA acids (C2–C10) account for 0.06–1.1 % of the total aerosol mass, with higher values in the summer, and 1.8 % of the total aerosol carbon in urban aerosol, in which (a)
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