Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles

Abstract

<p>Photoacoustic spectroscopy is a standout technique widely used for absorption measurements of atmospheric aerosols. Here we investigate the relative humidity dependence of photoacoustics and its implication for evaporation kinetics.</p>

Characterization and control of droplets optically trapped in air

“…We developed a feedback loop controlling the power balance of the two trapping beams to control the position of the trapped particles and to improve the confinement of particles 7 . As illustrated in Figure 1-b and 1-c, the power balance of the two trapping beams can be used to control the trapping position of single particles.…”

“…Two case studies are considered: photoacoustic spectroscopy of TEG particles (left column of Figure 3) and photochemistry of oleic acid particles (right column of Figure 3). The refractive index of TEG particles during the photoacoustic measurement is calculated by modeling the temperature of the particle and its water concentration as a function of the size of the particle 7 . Such size dependent refractive indices are necessary for a satisfactory fit of the Total TAOS for aqueous TEG particles.…”

“…However the importance of aerosol particles remains difficult to evaluate precisely because of their complexity. They show numerous physicochemical properties (size, shape, phase, chemical composition, viscosity, refractive index, pH, mass accommodation coefficient) and they are involved in complex processes, such as evaporation and condensation of gaseous species [5][6][7] , light scattering and absorption 8,9 , photochemistry 6,[10][11][12] , phase transitions [13][14][15] and phase separation 16,17 . Better understanding these processes is interesting for both applied and fundamental research.…”

“…A thorough characterization of particle properties is necessary to better understand the processes in which they are involved. Here the particle size is a key parameter affecting these processes in aerosol particles 7,17,[20][21][22] . We are developing multiple experiments to better control and characterize a single particle optically trapped in air:…”

“…In addition, these experiment can be coupled to obtain a more thorough characterization of single particles. The BLS 15,23 , Raman scattering 15 , photoacoustics 7,20,24 and digital holography 25,26 experiments have already been discussed in details elsewhere and will not be discussed further here. This paper explains the feedback control mechanism and the polarizationresolved TAOS measurements.…”