title: Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics.
abstract: 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.
authors.affiliation: Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
authors.forename: Johannes W
authors.initials: JW
authors.lastname: Cremer
authors.affiliation: Laboratory for Applied Laser Spectroscopy, Chair of Analytical Chemistry, Technical University of Munich, Marchioninistrasse 17, D-81377 Munich, Germany.
authors.forename: Klemens M
authors.initials: KM
authors.lastname: Thaler
authors.affiliation: Laboratory for Applied Laser Spectroscopy, Chair of Analytical Chemistry, Technical University of Munich, Marchioninistrasse 17, D-81377 Munich, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Haisch
authors.affiliation: Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
authors.forename: Ruth
authors.initials: R
authors.lastname: Signorell