Photodissociation of particulate nitrate as a source of daytime tropospheric Cl<sub>2</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35177585.
- Also identified by DOI 10.1038/s41467-022-28383-9 and PMC identifier 8854671.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl<sub>2</sub>), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl<sub>2</sub> concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl<sub>2</sub> (2.7 pptv s<sup>-1</sup> at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl<sub>2</sub> production. The high Cl<sub>2</sub> concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.