In situ Quantification of Ammonium Sulfate in Single Aerosol Droplets by Means of Laser Trapping and Raman Spectroscopy

Reversible Control of the Equilibrium Size of a Single Aerosol Droplet by Change in Relative Humidity

“…Raman scattering of the symmetric stretching vibration of an SO4 2-anion and the OH stretching vibration of H2O were observed at 980 and 3420 cm -1 , respectively. As described in a previous publication, the intensity ratio of these two Raman peaks (I980/I3420) is known to be linearly proportional to the ammonium sulfate concentration in water, 8,9 and the slope and intercept values of the calibration curve were determined to be 1.12 ± 0.01 dm 3 mol -1…”

“…Laser trapping and Raman spectroscopy of single aerosol droplets have been discussed in previous publications and will be described only briefly here. [8][9][10][11] Aerosol water droplets containing ammonium sulfate were generated by an ultrasonic nebuliser and introduced into a chamber set on the stage of an inverted optical microscope (Olympus, IX71). A single water droplet was trapped by focused laser light from a CW-Nd:YVO4 laser (532 nm, Coherent, Verdi) through an objective lens (×60, N.A.…”

“…1,2 Noncontact levitation of a single micrometer-sized water droplet in air can be achieved by a laser trapping technique. [3][4][5][6][7][8][9][10][11] Furthermore, a laser beam used as a trapping light source can be used simultaneously as an excitation light source for Raman spectroscopy, which provides information on a fingerprint of the chemical composition in an aerosol water droplet. Therefore, laser trapping and Raman spectroscopy is the powerful means to study the chemical and physical properties of single droplets in air.…”

“…12,13 As demonstrated in a previous publication, the ammonium sulfate concentrations in individual aerosol water droplets (0.07 -0.11 mol dm -3 ) generated by an ultrasonic nebulizer are independent of those in mother solutions (0.05 -1.00 mol dm -3 ) under constant relative humidity conditions. 8 This phenomenon is one of the characteristic features of the aerosol water droplets, and will not be observed in colloidal particles such as water-in-oil emulsions. The vapor pressures in aerosol droplets should be thermodynamically in equilibrium with that of water in air.…”

Temperature-induced Coalescence of Droplets Manipulated by Optical Trapping in an Oil-in-Water Emulsion

“…22 Recent studies have used laser trapping to observe freezing processes, conduct the measurement of Raman spectra, and to control size. [23][24][25] Droplets in an emulsion are expected to be a useful container of chemical reagents in droplet-based analytical methods. 26 In the present study, therefore, we examined the coalescence of oil droplets stabilized by a surfactant or a hydrophilic polymer in water using optical trapping.…”