Cloud activation of single‐component organic aerosol particles

Abstract

[1] The organic fraction of ambient aerosols is a complex mixture of hundreds of organic compounds varying in chemical structure and physical properties. The cloud condensation nuclei (CCN) activities of single-component organic particles were experimentally investigated. Activation diameters were determined using a Tandem Differential Mobility Analyzer and a thermal diffusion Cloud Condensation Nucleus Counter. Studies were performed at supersaturations of 0.3 and 1% with dry particle diameters ranging between 0.02 and 0.2 mm. The focus was on both hygroscopic secondary organics and hydrophobic primary organics. Laboratory experiments were performed with sodium chloride, ammonium sulfate, glutaric acid, adipic acid, pinonic acid, glutamic acid, leucine, cholesterol, pinic acid, norpinic acid, hexadecane, hexadecanol, myristic acid, palmitic acid, and stearic acid. The results were compared with the classical Köhler theory and a theory that accounts for the limited solubility of many organics. It was discovered that organic species with bulk solubilities in water less than 0.01 g cm À3 can be a good source of CCN in the atmosphere if their contact angles with water are zero. Experiments confirmed that Köhler theory works well in predicting activation of soluble inorganic species and organics that are wettable by water, while an extension of the theory appears necessary to account for the low-solubility organic species that are not wettable by water.

Water activity and activation diameters from hygroscopicity data - Part I: Theory and application to inorganic salts

“…The ratio of the vapor pressure of water over the drop to the saturation vapor pressure of water at that temperature, p o (T ), is known as the saturation ratio, s. The saturation ratio can be equated to the fractional ambient relative humidity, RH/100, if the droplet is in equilibrium with its environment. Equation (2) forms the basis of Köhler theory (Köhler, 1936), which in various forms has been used to theoretically predict the cloud condensation nucleating (CCN) activity of simple and complex aerosols in terms of their critical supersaturations (Giebl, 2002;Kumar et al, 2003;Prenni et al, 2001;Raymond and Pandis, 2002). A plot of s vs. D p , computed for a particular assumed mass of dry solute, generally has a maximum.…”

Closure between measured and modeled cloud condensation nuclei (CCN) using size-resolved aerosol compositions in downtown Toronto

“…A large number of laboratory studies have investigated the CCN behavior of soluble inorganic species such as ammonium sulfate and sodium chloride (Katz and Kocmond, 1973;Gerber et al, 1977). Recently, significant work has also been done with both soluble and insoluble organic species (Cruz and Pandis, 1997;Corrigan and Novakov, 1999;Giebl et al, 2002;Kumar et al, 2003;Raymond and Pandis, 2002;Broekhuizen et al, 2004a). Examples include low molecular weight dicarboxylic acids, oleic acid, and biogenic secondary organic aerosol (Broekhuizen et al, 2004b;VanReken et al, 2005).…”

SOA Formation Potential of Emissions from Soil and Leaf Litter

“…1,2 The presence of organics within atmospheric particles impacts climate by changing the aerosol radiative propertiesboth directly by impacting light scattering and absorption and indirectly by altering hygroscopicity and thus cloud-forming potential. 3,4 Consequently, accurate modeling of the organic aerosol component is crucial to properly assess the climate change impacts of the total atmospheric aerosol, one of the least understood of all climate change radiative forcers. 5 Among the many components contributing to the total atmospheric aerosol, secondary organic aerosol (SOA) is the most difficult to predict.…”