Direct imaging of changes in aerosol particle viscosity upon hydration and chemical aging

Abstract

We report quantitative, real-time, online observations of microscopic viscosity changes in aerosol particles of atmospherically relevant composition, using fluorescence lifetime imaging (FLIM) of viscosity.

Dynamic viscosity mapping of the oxidation of squalene aerosol particles

“…The aerosol has therefore changed from homogeneous to heterogeneous over the course of oxidation. This observation of increased heterogeneity within oxidised droplets closely mirrors our recent data on ozonolysis of oleic acid droplets deposited on the coverslip 17 . In these oxidised oleic acid droplets we also observed a significant widening of the lifetime histogram of embedded Bodipy-C10 during ozonolysis, more significant than could be expected from the lifetime increase alone, from 1.3 ± 0.1 ns (± 7.7%) to 4.2 ± 0.6 ns (± 14.5%).…”

“…A molecular rotor Bodipy-C10 that was previously well characterised for viscosity measurements in oleic acid droplets 17,20 , as well as in lipid vesicles [35][36][37] , was used for viscosity measurements. Bodipy-C10 is sensitive to a wide range of viscosities from 10 to 5000 mPa s, corresponding to fluorescence lifetime changes from 1 up to ca.…”

“…One of the limitations of our previous study by Hosny et al has been the use of droplets suspended on the microscope coverslip as model aerosol particles 17,20 . Since aerosol is a multiphase system composed of both a gas and a condensed phase, its physico-chemical properties including viscosity, can depend on the composition, state of matter, size, morphology, temperature and pressure of each of these phases.…”

“…At the same time, only few direct measurement methods are available for monitoring such properties 1, [6][7][8][9][10][11][12][13][14][15][16] . Recently, we have demonstrated that viscosity of model organic aerosols, such as oleic acid droplets, and secondary organic aerosols (SOA) produced from the oxidation of myrcene or -pinene can be measured and imaged in a spatially and time-resolved manner using Fluorescence Lifetime Imaging Microscopy (FLIM) of molecular rotors 17 . In our earlier study, 17 the droplets were deposited onto a glass coverslip for FLIM measurements.…”

Technical note: Monte Carlo genetic algorithm (MCGA) for model analysis of multiphase chemical kinetics to determine transport and reaction rate coefficients using multiple experimental data sets

“…In its first application the MCGA was used to fit individual data sets of the decay of oleic acid upon ozonolysis (Berkemeier et al, 2013), highlighting the need for fitting to multiple experimental data sets to constrain kinetic parameters. This was done in further studies that investigated gas uptake to (semi-)solid organic material in coated-wall flow-tube reactors (Arangio et al, 2015;Berkemeier et al, 2016), ozoneinduced protein oligomerization in bulk solutions (Kampf et al, 2015), viscosity change upon alkene ozonolysis as measured with fluorescence microscopy (Hosny et al, 2016), the redox-cycling reactions in the human lung lining fluid (Lakey et al, 2016a), and ozonolysis of squalene contained in human skin lipids (Lakey et al, 2016b). In each of these studies, a large set of model input parameters was optimized to several experimental data sets to constrain the input parameter space.…”