Organic acids as cloud condensation nuclei: Laboratory studies of highly soluble and insoluble species

Abstract

Abstract. The ability of sub-micron-sized organic acid particles to act as cloud condensation nuclei (CCN) has been examined at room temperature using a newly constructed continuous-flow, thermal-gradient diffusion chamber (TGDC). The organic acids studied were: oxalic, malonic, glutaric, oleic and stearic. The CCN properties of the highly soluble acids -oxalic, malonic and glutaric -match very closely Köhler theory predictions which assume full dissolution of the dry particle and a surface tension of the growing droplet equal to that of water. In particular, for supersaturations between 0.3 and 0.6, agreement between the dry particle diameter which gives 50% activation and that calculated from Köhler theory is to within 3 nm on average. In the course of the experiments, considerable instability of glutaric acid particles was observed as a function of time and there is evidence that they fragment to some degree to smaller particles. Stearic acid and oleic acid, which are both highly insoluble in water, did not activate at supersaturations of 0.6% with dry diameters up to 140 nm. Finally, to validate the performance of the TGDC, we present results for the activation of ammonium sulfate particles that demonstrate good agreement with Köhler theory if solution non-ideality is considered. Our findings support earlier studies in the literature that showed highly soluble organics to be CCN active but insoluble species to be largely inactive.

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

“…The O : C values were 1.19 and 1.24, and κ values were 0.20 and 0.21, for IOP1 and 2, respectively ( Table 1). The O : C and κ values are consistent with those of some typical SOA compounds, such as malonic acid, which has an O : C value of 1.33 and a κ value of 0.23 (Kumar et al, 2003), and succinic acid, which has an O : C value of 1 and a κ value of 0.23 (Hori et al, 2003). For the LO-OOA and IEPOX-SOA factors, the hygroscopicities vary between the two IOPs.…”

The hygroscopicity parameter (κ) of ambient organic aerosol at a field site subject to biogenic and anthropogenic influences: relationship to degree of aerosol oxidation

“…This is not unreasonable because HOA is thought to be hydrocarbon-like (Zhang et al, 2005a) and aliphatic in nature, and in general, these types of compounds have not been found to be CCN-active in laboratory experiments (e.g. Pradeep Kumar et al, 2003;Raymond and Pandis, 2002). In addition, ambient measurements of particles at locations in which HOA is high, especially at the smaller sizes, have shown that the organic component does not appear to contribute to the CCN-activity (Cubison et al, 2008;Quinn et al, 2008;Broekhuizen et al, 2006).…”

“…The cooler bottom plate was maintained at room temperature while the warmer upper plate was actively heated with a resistive heating pad (Omega) to the temperature required for the desired supersaturation as calculated and controlled by a Labview (National Instruments) program from the temperature of the cooler bottom plate. Like the chamber described by Pradeep Kumar et al (2003), this instrument has a movable injector that allows the residence time to vary from 9 to 21 s. The residence time of the chamber was adjusted to optimise the CCN concentration, which, for most of this study, occurred at 19 s. This time is a balance between giving the droplets sufficient time to grow to sizes large enough to be counted by the APS and preventing the aerosols from growing so large that they are lost to gravitational settling. The optimal residence time can also depend on the aerosol chemical composition.…”

“…This instrument, built at the University of Toronto, is a more portable and automated version of the design described by Pradeep Kumar et al (2003). It consists of two parallel aluminium plates held at different temperatures, which results in a supersaturation forming at the centre of the chamber (Saxena et al, 1970).…”

Analysis of cloud condensation nuclei composition and growth kinetics using a pumped counterflow virtual impactor and aerosol mass spectrometer

“…This typically involves (1) collection of cloudwater followed by offline chemical analysis (e.g. Parungo et al, 1982;Collett et al, 2002;Decesari et al, 2005;Hutchings et al, 2009) or (2) in situ sampling of cloud droplets followed by isolation of these droplets from the interstitial aerosol using a counterflow virtual impactor (CVI), evaporation of water from the droplet, and chemical analysis of the residual (e.g. Ogren et al, 1985;Noone et al, 1988;Heintzenberg et al, 1996;Twohy and Gandrud, 1998;Kamphus et al, 2010).…”