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

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.

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