An amorphous solid state of biogenic secondary organic aerosol particles

Abstract

Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs). On a global scale, biogenic VOCs account for about 90% of VOC emissions and of SOA formation (90 billion kilograms of carbon per year). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth's radiation balance and climate. They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas-particle partitioning models usually assume that SOA particles are liquid, but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid-most probably glassy-state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles' ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles. Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.

Oxidation of a model alkane aerosol by OH radical: the emergent nature of reactive uptake

“…In this context, well-mixed means behavior consistent with complete compositional uniformity. Recent studies [3][4][5][6] suggest that some organic aerosols exist in a glassy or semisolid phase, which can significantly affect the rates and mechanisms of the uptake of water 7,8 and other gas phase species as well as heterogeneous oxidation chemistry. 1 Laboratory studies of model systems are essential to unravel these factors and provide a rigorous foundation for climate model parameters.…”

Dynamic viscosity mapping of the oxidation of squalene aerosol particles

“…An aerosol's viscous state also has direct implications on the particle morphology, phase behaviour, optical properties, aging processes and lifetime. At the same time, only few direct measurement methods are available for monitoring such properties 1, [6][7][8][9][10][11][12][13][14][15][16] . Recently, we have demonstrated that viscosity of model organic aerosols, such as oleic acid droplets, and secondary organic aerosols (SOA) produced from the oxidation of myrcene or -pinene can be measured and imaged in a spatially and time-resolved manner using Fluorescence Lifetime Imaging Microscopy (FLIM) of molecular rotors 17 .…”

Evaluation of Particle Bounce in Various Collection Substrates to be Used as Vaporizer in Aerosol Mass Spectrometer

“…Physical properties of particles, such as hygroscopicity, size, density, phase, elasticity, and hardness, play an important role in particle bounce behavior (Wall et al 1990;Stein et al 1994;Matthew et al 2008;Virtanen et al 2010;Virtanen et al 2011;Bateman et al 2014). Hygroscopic particles, such as salts, are known to have much less bounce than non-hygroscopic particles (Stein et al 1994).…”

“…Several laboratory and field tests reported that a CE of less than 100% was mainly caused by particle bounce from the vaporizer, especially for solid particles (Jayne et al 2000;Huffman et al 2005;Quinn et al 2006;Liu et al 2007;Salcedo et al 2007). In addition, particle bounce has been considered as an important issue for impactor techniques that use the inertial force of particles (i.e., high impaction velocity) for sampling or separation (Virtanen et al 2010;Bateman et al 2014).…”