Accurate representations of the physicochemical properties of atmospheric aerosols: when are laboratory measurements of value?

Abstract

Laboratory studies can provide important insights into the processes that occur at the scale of individual particles in ambient aerosol. We examine the accuracies of measurements of core physicochemical properties of aerosols that can be made in single particle studies and explore the impact of these properties on the microscopic processes that occur in ambient aerosol. Presenting new measurements, we examine here the refinements in our understanding of aerosol hygroscopicity, surface tension, viscosity and optical properties that can be gained from detailed laboratory measurements for complex mixtures through to surrogates for secondary organic atmospheric aerosols.

Accuracy Required in Measurements of Refractive Index and Hygroscopic Response to Reduce Uncertainties in Estimates of Aerosol Radiative Forcing Efficiency

“…When determining the hygroscopic response of aerosol, Koehler et al () determined limiting values of κ of 0.33 and 0.72 from particle hygroscopicity measurements with a humidified tandem differential mobility analyzer (HTDMA) for AS aerosol. In recent paper, Rovelli et al () evaluated the accuracy of aerosol hygroscopic growth factor over a wide range in RH using a comparative kinetics cylindrical electrodynamic balance (CK‐EDB) for different aerosols, a technique that can also be applied to secondary organic aerosol samples (Marsh et al, ). In the case of AS, the uncertainty in κ was reduced to ±0.01.…”

Stability of Monoterpene-Derived α-Hydroxyalkyl-Hydroperoxides in Aqueous Organic Media: Relevance to the Fate of Hydroperoxides in Aerosol Particle Phases

“…In (10:90) mixtures, only a few clusters would contain a significant number of water molecules, those accounting for the fast -HH decay. Since microheterogeneity should be a general phenomenon in "internally mixed" aqueous organic mixtures, we suggest that the existence of inhomogeneities at the molecular level, as distinct from mesoscopic segregation, [63][64][65] could play unanticipated roles in atmospheric aqueous media. 56 The relatively short lifetimes of the -HHs derived from the ozonolysis of monoterpenes relative to the dramatic persistence of the -HH derived from -Tp (Table and Fig a  1/e = 1/k 1 catalyzed reaction.…”

Chemical signatures of surface microheterogeneity on liquid mixtures

“…1 Important natural processes also take place in aqueous organic media of complex compositions. [2][3][4] Solvents not only allow reactant molecules to get in close contact but also influence reactions in various ways and at different scales. 5 At one time, solvent effects in chemical reactions were rationalized in terms of transition state theory and continuous models based on macroscopic descriptors, such as solvent viscosity and dielectric constants.…”

“…40,41 These systems, which generally consist of water plus amphiphilic and hydrophobic organic species, can be internally mixed, phase-separated into aqueous cores covered by organic shells, or phase-separated into segregated aqueous and organic domains, depending on the inorganic solutes, temperature, relative humidity, and the abundance and functionality of organic species. 2,[42][43][44][45][46][47][48][49][50] It is apparent that the rates and products of the chemical processes associated with the formation, growth and aging of organic aerosols, and the exchange of gases between the atmosphere and the oceans may critically depend on whether organics are present as solutes in internally mixed or in phase-separated mixtures. In this context, phase separation refers to the meso/macroscale.…”