Title：Fluorescent Visualization of Chemical Profiles across AirWater Interface

Abstract: Chemical transfer across air-water interface is one of the most important geochemical processes of global significance. Quantifying such process has remained extremely challenging due to the lack of suitable technologies to measure chemical diffusion across air-water microlayer. Herein we present a fluorescence optical system capable of visualizing the formation of air-water microlayer with a spatial resolution of 10 μm and quantifying air-water diffusion fluxes using pyrene as a target chemical. We show for the first time air-water microlayer is composed of a surface microlayer in water ( ~290±40 μm) and a diffusion layer in air ( ~350±40 μm) with 1 μg L-1 of pyrene. Diffusion flux of pyrene across air-water interface is derived from its high-resolution concentration profile without any preemptive assumption, two orders of magnitude lower than those from the conventional method. This system can be expanded to visualize diffusion dynamics of other fluorescent chemicals across air-water interface, and provides a powerful tool for furthering our understanding of air-water mass transfer of organic chemicals related to their global cycling.

https://doi.org/10.1021/acs.est.3c03219