[pam-users] Gibbons et al., Anal. Chem., 2024; Boadu and Ohno, ES&T, 2026

[pam-users]

Angel M. Gibbons, Michael Boadu, and Paul E. Ohno, Aerosol Fluorescent Labeling via Probe Molecule Volatilization. Anal. Chem., 96(50), 19947-19954, https://doi.org/10.1021/acs.analchem.4c04291, 2024.

Abstract. The physicochemical properties of aerosols, including hygroscopicity, phase state, pH, and viscosity, influence important processes ranging from virus transmission and pulmonary drug delivery to atmospheric light scattering and chemical reactivity. Despite their importance, measurements of these key properties in aerosols remain experimentally challenging due to small particle sizes and low mass densities in air. Fluorescence probe spectroscopy is one of the only analytical techniques that is capable of experimentally determining these properties in situ in a nondestructive and minimally perturbative manner. However, the application of fluorescence probe spectroscopy to important classes of aerosols including exhaled respiratory and ambient atmospheric aerosols has been limited due to a typical reliance on premixing the probe molecule with particle constituents prior to particle generation, which is not always possible. Here, a method for aerosol fluorescent labeling based on probe molecule volatilization is developed. The method is first applied to label model polyethylene glycol (PEG) aerosols with two different polarity-sensitive probes, Nile red and Prodan. The similarity of the relative humidity-dependent fluorescent emission of each probe between prelabeled and volatilized-probe PEG particles validated the methodology. A preliminary application of the technique to indicate the hygroscopicity of artificial saliva respiratory particles and model atmospheric secondary organic aerosol particles is demonstrated. The methodology developed here paves the way for future studies applying powerful fluorescent probe-based analytical techniques to study exhaled or natural aerosols for which fluorescent prelabeling is not possible.

Michael Boadu and Paul E. Ohno. In Situ Physicochemical Characterization of Secondary Organic Aerosols via Fluorescence Probe Spectroscopy, Environ. Sci. Technol., 60(9), 7315-7325, https://doi.org/10.1021/acs.est.5c18022, 2026.

Abstract. Secondary organic aerosol (SOA) physicochemical properties such as hygroscopicity, degree of oxidation, phase state, pH, and viscosity influence important processes that ultimately impact air quality and climate. Due in part to the experimental challenge of in situ characterization, these physicochemical properties remain incompletely understood. Here, an aerosol fluorescent labeling methodology in conjunction with a fluorescence aerosol flow tube (F-AFT) was used for direct, in situ physicochemical characterization of α-pinene and toluene SOA. The wavelength of maximum emission λmax of the fluorescent probe Prodan was shown to depend on the hygroscopicity, degree of oxidation, and relative humidity (RH)-dependent phase transitions of the SOA. At varying RH, λmax was linearly correlated with % water content with an R2 value of 0.95. For fixed RH and varying SOA oxidation degree, λmax was linearly correlated with the oxygen-to-carbon ratio (O:C) with an R2 value of 0.95. Finally, the λmax values measured from mixed organic/inorganic particles indicated that ammonium sulfate seeded toluene SOA exhibited liquid-liquid phase separation (LLPS) at 80% RH and below while remaining homogeneous at 90% RH. Overall, this study demonstrates the power and versatility of this approach for direct, online analysis of a range of physicochemical properties in SOA.

PAM Wiki - Publications Using the PAM Oxidation Flow Reactor<https://sites.google.com/site/pamwiki/publications-using-the-pam-oxidation-flow-reactor>

Andrew Lambe, PhD, PMP
Principal Scientist
Center for Aerosol and Cloud Chemistry
Aerodyne Research, Inc.
45 Manning Rd., Billerica, MA, 01821
+1-978-663-9500 x 209

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