Complex refractive index of vanillic acid aerosol retrieved from 270–600 nm using aerosol extinction and solution phase absorption measurements

Abstract

The complex refractive index of vanillic acid, a component of biomass burning emission, in aerosol form generated by atomization is determined from optical measurements over the wavelength range of 270–600 nm. The aerosol extinction differential optical absorption spectrometer (AE-DOAS) measured the extinction spectrum. In addition, the polydisperse particle size distribution is obtained by the differential mobility analyzer and condensation particle counter. Experimental results combined with Mie theory are utilized to retrieve the real part of the complex refractive index while the outcome of a complementary UV-Vis solution phase absorption experiment is used to determine the imaginary part. The obtained values for the real and imaginary parts across the wavelengths are in the range of 1.43–1.65 and 0.000–0.388, respectively. The dependence of vanillic acid absorption on wavelength is strong at short wavelengths. The absorption Ångstrӧm exponent value between 300–500 nm is found to be 5.9 ± 0.6, which agrees with the previously reported values for brown carbon. Comparing the obtained n values of this work with the previously reported values for organic and brown carbon shows good agreement.

Copyright © 2024 American Association for Aerosol Research

EDITOR:

• Hans Moosmüller

Acknowledgements

This work was supported by the University of New Hampshire (UNH) Graduate School, College of Engineering and Physical Sciences, Department of Chemistry, and UNH Summer Teaching Assistant Fellowship (STAF) to V.H. V.H. has included a previous version of this work in his doctoral dissertation defended in Spring 2023 and to be published in Summer 2025. Implementation and coding of the Mie Theory model was achieved with the help of Mr. Tod Hagan using original source code from Dr. Sonia Kreidenweis. The authors would also like to thank Dr. Carolyn E. Jordan for her preliminary work to collect and critical observations of the extinction spectra of wet generated vanillic acid aerosol. The authors give special thanks to the reviewers and editor who helped to improve our paper with their keen and insightful questions.

Disclosure statement

The authors declare there is no Complete of Interest at this study.

Additional information

Funding

This work was funded by the University of New Hampshire, College of Engineering and Physical Sciences, Graduate School and the Department of Chemistry.