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arXiv · 2012.11112

Ionic-strength and pH dependent reactivities of ascorbic acid toward ozone in aqueous micro-droplets studied by aerosol optical tweezers

Yuan-Pin Chang·Shan-Jung Wu·Min-Sian Lin·Che-Yu Chiang·Genin Gary Huang
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Abstract

The heterogeneous oxidation reaction of single aqueous ascorbic acid (AH$_2$) aerosol particles with gas-phase ozone was investigated in this study utilizing aerosol optical tweezers with Raman spectroscopy. The measured liquid-phase bimolecular rate coefficients of the AH$_2$ + O$_3$ reaction exhibit a significant pH dependence, and the corresponding values at ionic strength 0.2 M are $(3.1 \pm 2.0) \times 10^5$ M$^{-1}$s$^{-1}$ and $(1.2 \pm 0.6) \times 10^7$ M$^{-1}$s$^{-1}$ for pH $\approx$ 2 and 6, respectively. These results measured in micron-sized droplets agree with those from previous bulk measurements, indicating that the observed aerosol reaction kinetics can be solely explained by liquid phase diffusion and AH$_2$ + O$_3$ reaction. Furthermore, the results indicate that high ionic strengths could enhance the liquid-phase rate coefficients of the AH$_2$ + O$_3$ reaction. The results also exhibit a negative ozone pressure dependence that can be rationalized in terms of a Langmuir-Hinshelwood type mechanism for the heterogeneous oxidation of AH$_2$ aerosol particles by gas-phase ozone. The results of the present work imply that in acidified airway-lining fluids the antioxidant ability of AH$_2$ against atmospheric ozone will be significantly suppressed.

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Yuan-Pin Chang, Shan-Jung Wu, Min-Sian Lin, Che-Yu Chiang, Genin Gary Huang. 2020-12-21. Ionic-strength and pH dependent reactivities of ascorbic acid toward ozone in aqueous micro-droplets studied by aerosol optical tweezers. https://doi.org/10.1039/d0cp06493a

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