Photo-oxidation of particle phase iron species dominates the generation of reactive oxygen species in secondary aerosol

Sabrina Yanan Jiang; Nirmal Kumar Gali; Huada Daniel Ruan; Zhi Ning

doi:10.1016/j.scitotenv.2020.137994

Photo-oxidation of particle phase iron species dominates the generation of reactive oxygen species in secondary aerosol

Sci Total Environ. 2020 Jun 25:723:137994. doi: 10.1016/j.scitotenv.2020.137994. Epub 2020 Mar 23.

Authors

Sabrina Yanan Jiang¹, Nirmal Kumar Gali², Huada Daniel Ruan³, Zhi Ning⁴

Affiliations

¹ Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong; Division of Science and Technology, Beijing Normal University-Hong Kong Baptist University United International College, China.
² Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong.
³ Division of Science and Technology, Beijing Normal University-Hong Kong Baptist University United International College, China.
⁴ Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong. Electronic address: zhining@ust.hk.

PMID: 32224395
DOI: 10.1016/j.scitotenv.2020.137994

Abstract

This study presents an experimental investigation on the photochemical transformation of iron species in aerosol including dissolution of insoluble iron species into soluble fraction, and soluble ferric oxidation to ferrous form. This process has significantly contributed to the aerosol oxidative potential in generation of reactive oxygen species (ROS). We conducted both laboratory experiment of UV irradiation and real world solar irradiation on large variation of aerosol samples for the characterization of iron speciation in insoluble and soluble fractions to investigate their transformation under photooxidation process. The results showed that the real world solar irradiation significantly increased the soluble Fe(II) fraction, and this is corroborated by laboratory simulation of UV irradiation showing increasing soluble Fe(II) fraction with elongating aging time. The results further exhibited that the dissolution of iron component into soluble fraction was a dominant process, followed by the conversion of soluble ferric to ferrous ions. Further, the study confirmed that the oxidative potential of particulate matter (PM) is attributed dominantly to the abundance of transition metals, i.e. Fe, and the incremental ROS generation after photochemical process is attributed largely to the transformation of solid phase iron species to soluble Fe(II). The results suggest that transition metals, for example by iron in this study, play an important role in secondary aerosol process.

Keywords: Iron; Reactive oxygen species; Secondary aerosol; Solar irradiation; UV irradiation.