Chlorine activation indoors and outdoors via surface-mediated reactions of nitrogen oxides with hydrogen chloride

Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NOy) are also globally distributed, because NO formed in combustion processes is oxidized to NO₂, HNO₃, N₂O₅ and a variety of other nitrogen oxides during transport. Deposition of HCl an...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2009-08, Vol.106 (33), p.13647-13654
Main Authors: Raff, Jonathan D, Njegic, Bosiljka, Chang, Wayne L, Gordon, Mark S, Dabdub, Donald, Gerber, R. Benny, Finlayson-Pitts, Barbara J
Format: Article
Language:English
Subjects:
Air Pollutants - analysis
Air pollution
Atmospheric chemistry
Atmospherics
Boundary layers
Cadmium
Chemical reactions
Chlorides
Chlorine
Chlorine - chemistry
Combustion
Environmental Monitoring - methods
Gases
Greenhouse gases
Human computer interaction
Hydrochloric acid
Hydrochloric Acid - chemistry
Hydrogen
Hydrolysis
Indoor environments
Marine chemistry
Models, Chemical
Molecular Conformation
Molecules
Nitric oxide
Nitrogen
Nitrogen - chemistry
Nitrogen oxides
Nitrogen Oxides - chemistry
Oxidants
Oxidants - chemistry
Oxidation
Oxides
Ozone
Photochemicals
Physical Sciences
Salts
Spectroscopy, Fourier Transform Infrared
Surface Properties
Water vapor
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Summary:Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NOy) are also globally distributed, because NO formed in combustion processes is oxidized to NO₂, HNO₃, N₂O₅ and a variety of other nitrogen oxides during transport. Deposition of HCl and NOy onto surfaces is commonly regarded as providing permanent removal mechanisms. However, we show here a new surface-mediated coupling of nitrogen oxide and halogen activation cycles in which uptake of gaseous NO₂ or N₂O₅ on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO₂), respectively. These are potentially harmful gases that photolyze to form highly reactive chlorine atoms. The reactions are shown both experimentally and theoretically to be enhanced by water, a surprising result given the availability of competing hydrolysis reaction pathways. Airshed modeling incorporating HCl generated from sea salt shows that in coastal urban regions, this heterogeneous chemistry increases surface-level ozone, a criteria air pollutant, greenhouse gas and source of atmospheric oxidants. In addition, it may contribute to recently measured high levels of ClNO₂ in the polluted coastal marine boundary layer. This work also suggests the potential for chlorine atom chemistry to occur indoors where significant concentrations of oxides of nitrogen and HCl coexist.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0904195106