A light-driven burst of hydroxyl radicals dominates oxidation chemistry in newly activated cloud droplets

Suzanne E Paulson; Peter J Gallimore; Xiaobi M Kuang; Jie Rou Chen; Markus Kalberer; David H Gonzalez

doi:10.1126/sciadv.aav7689

A light-driven burst of hydroxyl radicals dominates oxidation chemistry in newly activated cloud droplets

Sci Adv. 2019 May 1;5(5):eaav7689. doi: 10.1126/sciadv.aav7689. eCollection 2019 May.

Authors

Suzanne E Paulson¹, Peter J Gallimore², Xiaobi M Kuang¹, Jie Rou Chen¹, Markus Kalberer^{2

3}, David H Gonzalez¹

Affiliations

¹ Department of Atmospheric and Oceanic Sciences, University of California at Los Angeles, Los Angeles, CA 90095-1565, USA.
² Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
³ Department of Environmental Sciences, University of Basel, Klingelbergstrasse 27, 4056 Basel, Switzerland.

Abstract

Aerosol particles and their interactions with clouds are one of the most uncertain aspects of the climate system. Aerosol processing by clouds contributes to this uncertainty, altering size distributions, chemical composition, and radiative properties. Many changes are limited by the availability of hydroxyl radicals in the droplets. We suggest an unrecognized potentially substantial source of OH formation in cloud droplets. During the first few minutes following cloud droplet formation, the material in aerosols produces a near-UV light-dependent burst of hydroxyl radicals, resulting in concentrations of 0.1 to 3.5 micromolar aqueous OH ([OH]_aq). The source of this burst is previously unrecognized chemistry between iron(II) and peracids. The contribution of the "OH burst" to total OH in droplets varies widely, but it ranges up to a factor of 5 larger than previously known sources. Thus, this new process will substantially enhance the impact of clouds on aerosol properties.