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Continuing efforts to quantify the influence of aerosol light absorption upon global heat budgets rely on high-quality measurements of aerosol optical properties. Of the available methods, photoacoustic spectroscopy stands out as a sensitive method for measurements of aerosol absorption with minimal sample modification. Theoretical treatments of photoacoustic aerosol detection have predicted size-dependent damping of the photoacoustic signal as a result of particle thermal inertia. We provide experimental confirmation of this prediction using a single-particle photoacoustic spectrometer, which allows us to measure photoacoustic signals with high sensitivity and size-specificity. Both the magnitude and phase of the photoacoustic response follow the linearized description of the heat flux. The quantification of this effect provides a basis for future, system-specific case studies.

Optical confinement (OC) structures the optical field and amplifies light intensity inside atmospheric aerosol particles, with major consequences for sunlight-driven aerosol chemistry. Although theorized, the OC-induced spatial structuring has so far defied experimental observation. Here, x-ray spectromicroscopic imaging complemented by modeling provides direct evidence for OC-induced patterning inside photoactive particles. Single iron(III)–citrate particles were probed using the iron oxidation state as a photochemical marker. Based on these results, we predict an overall acceleration of photochemical reactions by a factor of two to three for most classes of atmospheric aerosol particles. Rotation of free aerosol particles and intraparticle molecular transport generally accelerate the photochemistry. Given the prevalence of OC effects, their influence on aerosol particle photochemistry should be considered by atmospheric models.

the partitioning of components between droplets and the gas phase in e-cigarette aerosols has a significant impact on deposition within the respiratory tract. However, exclusive detection of droplet composition has, so far, been elusive. consequently, the dynamics of partitioning between droplets and the gas phase remains unknown. Here, we combine optical trapping of single droplets with in situ Raman scattering for destruction-free monitoring of e-cigarette droplet composition with a time resolution of seconds. We find that the initial droplet composition is very close to the composition of the e-liquid. Upon dilution with air, the droplet composition changes exponentially on a time scale of seconds, mainly because of evaporation of propylene glycol. the nicotine content in the droplet is controlled by the pH. Nicotine evaporates from the droplets under basic conditions, but remains in the liquid under acidic conditions. these results are crucial for advancing e-liquid research and manufacturing. Electronic cigarettes (e-cigarettes) represent a multibillion dollar industry 1 and a fast growing market 2. The ongoing debates on e-cigarettes have made it very clear that more studies are needed 3,4 for better assessing their health effects and potential to reduce the risk of smoking-related diseases as compared to continued smoking 5-8 and, eventually, for designing products 4. E-cigarettes are devices designed to deliver nicotine to the user through aerosol droplets generated by heating up a liquid called "e-liquid". Most e-liquids are composed of propylene glycol (PG), vegetable glycerol (VG), nicotine, flavoring supplements, and water 9,10. Heating such an e-liquid evaporates all of its chemical compounds into the gas phase. When the gas phase cools down, liquid aerosol droplets are formed by condensation of the vapor. The different components of the e-liquid are then present both in the droplet and gas phases of the aerosol. Many studies have underlined the importance of and need for knowing which components remain in the droplet phase and which evaporate again into the gas phase 11-14. The partitioning of components between the droplet and gas phases, for example, affects their deposition in the respiratory tract 11-14. Yet, the dynamics of compound transfer between the droplet and gas phases remains largely unknown, mainly because of the lack of adequate in situ methods for exclusively probing the composition of the droplets in the aerosol with adequate time resolution. A few simulations have addressed this topic 11,13 , but, to the best of our knowledge, no corresponding experimental data are available. Many experimental methods measure the chemical composition of the whole e-cigarette aerosol, i. e. without distinction between the droplet and gas phases and without time resolution. Most measurements are off-line measurements that first sample the e-cigarette aerosol and then use ex situ analysis methods, typically chromatography and/or mass spectroscopy 1,14,15. These off-line measurements usually sample bot...

In this contribution we present experiments used to control and characterize single optically trapped aerosol particles. These experiments include a counter-propagating optical tweezer, a feedback control mechanism to stabilize the particle in the trap and a two-angle optical scattering measurement to monitor the time-evolution of the particle size. Experimental setups and results are presented for these experiments.