pH modifies the oxidative potential and peroxide content of biomass burning HULIS under dark aging

Chunlin Li; Zheng Fang; Hendryk Czech; Eric Schneider; Christopher P Rüger; Michal Pardo; Ralf Zimmermann; Jianmin Chen; Alexandre Laskin; Yinon Rudich

doi:10.1016/j.scitotenv.2022.155365

pH modifies the oxidative potential and peroxide content of biomass burning HULIS under dark aging

Sci Total Environ. 2022 Aug 15:834:155365. doi: 10.1016/j.scitotenv.2022.155365. Epub 2022 Apr 21.

Authors

Affiliations

¹ Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address: chunlin.li@weizmann.ac.il.
² Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
³ Joint Mass Spectrometry Centre, Institute of Chemistry, University of Rostock, 18059 Rostock, Germany; Joint Mass Spectrometry Centre, Comprehensive Molecular Analytics, Helmholtz Zentrum München, 81379 München, Germany.
⁴ Joint Mass Spectrometry Centre, Institute of Chemistry, University of Rostock, 18059 Rostock, Germany.
⁵ Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Institute of Atmospheric Sciences, Fudan University, Shanghai 200438, China.
⁶ Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
⁷ Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address: yinon.rudich@weizmann.ac.il.

PMID: 35460777
DOI: 10.1016/j.scitotenv.2022.155365

Abstract

Humic-like substances (HULIS) account for a major redox-active fraction of biomass burning organic aerosols (BBOA). During atmospheric transport, fresh acidic BB-HULIS in droplets and humid aerosols are subject to neutralization and pH-modified aging process. In this study, solutions containing HULIS isolated from wood smoldering emissions were first adjusted with NaOH and NH₃ to pH values in the range of 3.6-9.0 and then aged under oxic dark conditions. Evolution of HULIS oxidative potential (OP) and total peroxide content (equivalent H₂O₂ concentration, H₂O₂eq) were measured together with the changes in solution absorbance and chemical composition. Notable immediate responses such as peroxide generation, HULIS autoxidation, and an increase in OP and light absorption were observed under alkaline conditions. Initial H₂O₂eq, OP, and absorption increased exponentially with pH, regardless of the alkaline species added. Dark aging further oxidized the HULIS and led to pH-dependent toxic and chemical changes, exhibiting an alkaline-facilitated initial increase followed by a decrease of OP and H₂O₂eq. Although highly correlated with HULIS OP, the contributions of H₂O₂eq to OP are minor but increased both with solution pH and dark aging time. Alkalinity-assisted autoxidation of phenolic compounds and quinoids with concomitant formation of H₂O₂ and other alkalinity-favored peroxide oxidation reactions are proposed here for explaining the observed HULIS OP and chemical changes in the dark. Our findings suggest that alkaline neutralization of fresh BB-HULIS represents a previously overlooked peroxide source and pathway for modifying aerosol redox-activity and composition. Additionally, these findings imply that the lung fluid neutral environment can modify the OP and peroxide content of inhaled BB-HULIS. The results also suggest that common separation protocols of HULIS using base extraction methods should be treated with caution when evaluating and comparing their composition, absorption, and relative toxicity.

Keywords: Aqueous aging; Autoxidation; Biomass burning HULIS; Oxidative potential; Peroxides; pH influence.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Biomass
Environmental Monitoring
Humic Substances / analysis
Hydrogen Peroxide
Hydrogen-Ion Concentration
Oxidation-Reduction
Oxidative Stress
Particulate Matter* / analysis
Peroxides

Substances

Aerosols
Air Pollutants
Humic Substances
Particulate Matter
Peroxides
Hydrogen Peroxide