Johannes Cremer

Last Name

Cremer

First Name

Johannes

ORCID

0000-0003-4247-4661

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Publications 1 - 10 of 10

Photoacoustic measurements of photokinetics in single optically trapped aerosol droplets
Covert, Paul; Cremer, Johannes; Signorell, Ruth; et al. (2017)
Geophysical Research Abstracts
Photoacoustic Spectroscopy of Single Optically Trapped Aerosol Droplets
Cremer, Johannes (2019)
Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles
Diveky, Matus; Roy, Sandra; Cremer, Johannes; et al. (2019)
Physical Chemistry Chemical Physics
Photoacoustic spectroscopy is widely used to measure the light absorption of aerosols. However, the impact of key factors such as the effect of relative humidity and mass exchange on photoacoustic measurements are still poorly understood. We assess such measurement biases and their physical origin by analysing the photoacoustic signal of single tetraethylene glycol (TEG) particles at varying relative humidities. Our results show a decrease in the photoacoustic signal at elevated relative humidities for small particles (0.8–1.5 μm), while for larger sizes (2.2–3.2 μm) the trend is reversed. We model the photoacoustic signal to interpret the observed behaviour in terms of mass and heat flux contribution. The single particle photoacoustic signal analysis presented in this paper additionally allows for the retrieval of the mass accommodation coefficient. Fitting our experimental data to the theoretical model reveals values of αM ≈ 0.02–0.005 for water on TEG in the temperature range 295–309 K.
Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics
Cremer, Johannes; Thaler, Klemens M.; Haisch, Christoph; et al. (2016)
Nature Communications
Photochemistry taking place in atmospheric aerosol droplets has a significant impact on the Earth’s climate. Nanofocusing of electromagnetic radiation inside aerosols plays a crucial role in their absorption behaviour, since the radiation flux inside the droplet strongly affects the activation rate of photochemically active species. However, size-dependent nanofocusing effects in the photokinetics of small aerosols have escaped direct observation due to the inability to measure absorption signatures from single droplets. Here we show that photoacoustic measurements on optically trapped single nanodroplets provide a direct, broadly applicable method to measure absorption with attolitre sensitivity. We demonstrate for a model aerosol that the photolysis is accelerated by an order of magnitude in the sub-micron to micron size range, compared with larger droplets. The versatility of our technique promises broad applicability to absorption studies of aerosol particles, such as atmospheric aerosols where quantitative photokinetic data are critical for climate predictions.
Photoacoustic absorption spectroscopy of single optically trapped aerosol droplets
Covert, Paul A.; Cremer, Johannes; Signorell, Ruth (2017)
Proceedings Volume 10347, Optical Trapping and Optical Micromanipulation XIV, 1034729 (2017)
Fundamental investigation of photoacoustic signal generation from single aerosol particles at varying relative humidity
Diveky, Matus; Roy, Sandra; David, Grégory; et al. (2020)
Photoacoustics
Photoacoustic (PA) spectroscopy enjoys widespread applications across atmospheric sciences. However, experimental biases and limitations originating from environmental conditions and particle size distributions are not fully understood. Here, we combine single-particle photoacoustics with modulated Mie scattering to unravel the fundamental physical processes occurring during PA measurements on aerosols. We perform measurements on optically trapped droplets of varying sizes at different relative humidity. Our recently developed technique – photothermal single-particle spectroscopy (PSPS) – enables fundamental investigations of the interplay between the heat flux and mass flux from single aerosol particles. We find that the PA phase is more sensitive to water uptake by aerosol particles than the PA amplitude. We present results from a model of the PA phase, which sheds further light onto the dependence of the PA phase on the mass flux phenomena. The presented work provides fundamental insights into photoacoustic signal generation of aerosol particles.
Correction: Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles (vol 21, pg 4721, 2019)
Diveky, Matus; Roy, Sandra; Cremer, Johannes; et al. (2020)
Physical Chemistry Chemical Physics
Characterization and control of droplets optically trapped in air
David, Grégory; Reich, Oliver; Diveky, Matus; et al. (2019)
Proceedings Volume 11083, Optical Trapping and Optical Micromanipulation XVI 1108322 (2019)
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.
Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces
David, Grégory; Esat, Kivanç; Hartweg, Sebastian; et al. (2015)
The Journal of Chemical Physics
Direct Measurement of Photoacoustic Signal Sensitivity to Aerosol Particle Size
Cremer, Johannes; Covert, Paul A.; Parmentier, Evelyne A.; et al. (2017)
The Journal of Physical Chemistry Letters

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Johannes Cremer

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