Abiotic interfacial photochemistry of biogenic surfactants as a major source of volatile organic compounds
Résumé
Surfaces coated with biogenic surfactants exposed to the atmosphere are ubiquitous
and are commonly present on aerosol particles, cloud droplets, buildings, plants, and
oceans. As shown in the past, photochemical reactions taking places at these air/water
interfaces lead to unique chemical pathways, producing volatile organic compounds
(VOCs) and leading to secondary organic aerosol formation.
Here, photochemical processes at the air/water interface of biofilm-containing
solutions were studied, demonstrating abiotic VOC production from authentic biogenic
surfactants under ambient conditions [1]. Using a combination of online-APCI-HRMS
and PTR-ToF-MS, unsaturated and functionalized VOCs were identified and quantified,
giving emission fluxes comparable to previous field and laboratory observations.
Interestingly, VOC fluxes increased with the decay of microbial cells in the samples,
indicating that cell lysis due to cell death was the main source for surfactants, and VOC
production. In agreement with our previous studies, LC-MS measurements of the liquid
phase suggested the presence of fatty acids and known photosensitizers, possibly
inducing the observed VOC production via peroxy-radical chemistry. Up to now, such
VOC emissions were directly attributed to high biological activity in surface water.
However, our results suggest that abiotic photochemistry can lead to similar
atmospheric emissions, especially in low biologically-active regions. Furthermore,
chamber experiments suggested that oxidation (O3 /OH-radicals) of the
photochemically-produced VOCs leads to aerosol formation and growth, possibly
affecting atmospheric chemistry and climate-related processes, such as cloud
formation or the Earth’s radiation budget.
[1] M. Brüggemann et al., Faraday Discussions, 2017, in press.