Oxidative aging of mixed oleic acid/sodium chloride aerosol particles

Abstract

.[1] Studies of the oxidative aging of single mixed component aerosol particles formed from oleic acid (OL) and sodium chloride over a range of relative humidities (RH) and ozone concentrations by aerosol optical tweezers are reported. The rate of loss of OL and changes in the organic phase volume are directly measured, comparing particles with effloresced and deliquesced inorganic seeds. The kinetics of the OL loss are analyzed and the value of the reactive uptake coefficient of ozone by OL is compared to previous studies. The reaction of OL is accompanied by a decrease in the particle volume, consistent with the evaporation of semivolatile products over a time scale of tens of thousands of seconds. Measurements of the change in the organic phase volume allow the branching ratio to involatile components to be estimated; between 50 and 85% of the initial organic volume remains involatile, depending on ozone concentration. The refractive index (RI) of the organic phase increases during and after evaporation of volatile products, consistent with aging followed by a slow restructuring in particle morphology. The hygroscopicity of the particle and kinetics of the response of the organic phase to changes in RH are investigated. Both size and RI of unoxidized and oxidized particles respond promptly to RH changes with values of the RI consistent with linear mixing rules. Such studies of the simultaneous changes in composition and size of mixed component aerosol provide valuable data for benchmarking kinetic models of heterogeneous atmospheric aging.Citation: Dennis-Smither, B. J., R. E. H. Miles, and J. P. Reid (2012), Oxidative aging of mixed oleic acid/sodium chloride aerosol particles,

Accurate and efficient determination of the radius, refractive index, and dispersion of weakly absorbing spherical particle using whispering gallery modes

“…As a second set of data, we considered the oxidative aging of oleic acid/sodium chloride particles [19,20]. In this experiment, a trapped particle consisting of a sodium chloride core and a thick oleic acid coating is exposed to ozone.…”

“…If the droplet is assumed to be both homogeneous and spherical, the resonance wavelengths of WGMs can be used to simultaneously determine both radius and refractive index with very high precision [7,12,14]. Then, the fundamental processes of evaporation/condensation, phase change, and oxidative aging can be directly studied through changes to the radius or refractive index of a particle [15][16][17][18][19][20].…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…82,93 Additionally, Reid and coworkers investigated oxidative aging of aerosol particles containing environmentally relevant organic acids using optical tweezers and cavity enhanced ringdown spectroscopy. 94,95 For mixed NaCl/oleic acid particles, they report an uptake coefficient of 2.3 Â 10…”

Deviations from Plane-Wave Mie Scattering and Precise Retrieval of Refractive Index for a Single Spherical Particle in an Optical Cavity

“…Studies on single particles, confined within optical or electrodynamic traps, now provide precise measurements of aerosol refractive indices and phases, hygroscopic growth, evaporation of semi-volatile components, and other properties of importance for their atmospheric behaviour. [2][3][4][5][6] These trapping-based techniques are most applicable to single particles with radii greater than 1 μm, but the smaller accumulation mode particles are of greater significance for atmospheric processes. 4 In a recent publication, we demonstrated that absolute extinction cross sections for single submicron radius spherical aerosol particles can be measured with high precision by combining optical confinement and levitation of a particle with cavity ring-down spectroscopy (CRDS).…”