Photoproduction of reactive intermediates from dissolved organic matter in coastal seawater around an urban metropolis in South China: Characterization and predictive modeling

Yitao Li; Kai Zhang; Jennifer Apell; Yuefei Ruan; Xinming Huang; Theodora Nah

doi:10.1016/j.scitotenv.2024.170998

Photoproduction of reactive intermediates from dissolved organic matter in coastal seawater around an urban metropolis in South China: Characterization and predictive modeling

Sci Total Environ. 2024 Apr 15:921:170998. doi: 10.1016/j.scitotenv.2024.170998. Epub 2024 Feb 15.

Authors

Yitao Li¹, Kai Zhang², Jennifer Apell³, Yuefei Ruan⁴, Xinming Huang⁵, Theodora Nah⁶

Affiliations

¹ School of Energy and Environment and State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong. Electronic address: yitaoli2-c@my.cityu.edu.hk.
² National Observation and Research Station of Coastal Ecological Environments in Macao, Macao Environmental Research Institute, Macau University of Science and Technology, Macao. Electronic address: zhangkai@must.edu.mo.
³ Department of Civil and Urban Engineering, New York University Tandon School of Engineering, 6 Metrotech Center, Brooklyn, New York, USA. Electronic address: japell@nyu.edu.
⁴ State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong. Electronic address: yruan8@cityu.edu.hk.
⁵ School of Energy and Environment and State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong. Electronic address: xinmhuang3@cityu.edu.hk.
⁶ School of Energy and Environment and State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong. Electronic address: theodora.nah@cityu.edu.hk.

PMID: 38365044
DOI: 10.1016/j.scitotenv.2024.170998

Abstract

Chromophoric dissolved organic matter (CDOM) is an important photochemical precursor to reactive intermediates (RIs) (e.g., excited triplet states of chromophoric dissolved organic matter (³CDOM^⁎), hydroxyl radicals (·OH), and singlet oxygen (¹O₂)) in aquatic systems to drive the photodegradation of contaminants. There have been limited studies on the photoproduction of RIs in coastal seawater CDOM in Asia, which impedes our ability to model the lifetimes and fates of contaminants in these coastal seawater systems. Hong Kong is an urban metropolis in South China, whose coastal seawater is susceptible to anthropogenic activities from the surrounding areas and the nearby Pearl River. We investigated the photoproduction of RIs in seawater around Hong Kong during the wet vs. dry season. Higher intensities of fluorescent components, dissolved organic carbon concentration ([DOC]), apparent quantum yields of RIs (Φ_RIs), and steady-state concentrations of photogenerated RIs ([RIs]_ss) were observed for samples collected in the areas closest to the Pearl River during the wet season. Lower humification degrees and Φ_RIs but higher intensities of fluorescent components and [RIs]_ss were generally observed for the wet season samples compared to the dry season samples. Statistical analysis revealed strong significant correlations (Spearman |r| > 0.6, p < 0.05) between Φ_RIs and the absorbance properties (including the absorbance ratio E₂:E₃, spectral slope coefficients S₃₅₀_-₄₀₀, and spectral slope ratio S_R) of CDOM, and between [RIs]_ss and the quantity-reflected properties (including the fluorescence intensity of humic-like components) of CDOM. Our modeling analyses combining orthogonal partial least squares and stepwise multiple linear regression showed excellent prediction strengths for [¹O₂]_ss and [³CDOM^⁎]_ss (R²_adj > 0.7) when [DOC] and the chemical and optical properties of CDOM were used as predictor variables. These modeling results demonstrate the feasibility of predicting the concentrations and quantum yields of RIs in seawater around Hong Kong, and potentially other coastal cities in South China, from easily measurable chemical and optical properties.

Keywords: Apparent quantum yield; Dissolved organic matter; Photochemistry; Reactive intermediates; Surface coastal seawater.