Photolytic oxidation of ammonium chloride as a source of Cl<sub>2</sub> in the atmosphere.
basic_science · Level V
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- Record sourced from PubMed, PMID 41896545.
- Also identified by DOI 10.1038/s41467-026-70941-y.
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Abstract
Chlorine atoms (·Cl) exhibit high reactivity and exert a substantial influence on the atmospheric oxidation capacity and chlorine cycle in the troposphere. The photolysis of molecular chlorine (Cl<sub>2</sub>) is a crucial source of ·Cl. However, the daytime peaks of Cl<sub>2</sub> concentration cannot be entirely accounted for by the currently known pathways. Here we show that the photolytic oxidation of ammonium chloride (NH<sub>4</sub>Cl), a ubiquitous component of atmospheric aerosol, serves as an important daytime source of Cl<sub>2</sub>. Laboratory experiments demonstrate that oxygen, water vapour, and acidity are indispensable for Cl<sub>2</sub> generation and release, and that Cl<sub>2</sub> production is enhanced in the presence of black carbon aerosol. Field observation combined with model simulation demonstrates that the mechanism explains 12-55% of daytime Cl<sub>2</sub> concentration. These results reveal a photoactivation pathway for chlorine production that depends only on chlorine salts and solar radiation, with significant implications in regions with abundant chloride salts.