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Addicted to Salt: Mass Spectrometry Reveals Chlorine Chemistry Degrading Wintertime Air Quality

Kerri Pratt
Tuesday, October 11, 2022
4:00-5:30 PM
1640 Chemistry Dow Lab Map
Chlorine radicals (Cl·) readily react with the greenhouse gas methane and other volatile hydrocarbons, facilitating the production of ozone and particulate matter that degrade air quality and harm human health. An important chlorine source is the photolysis of nitryl chloride (ClNO2(g)), which is formed in the polluted atmosphere at night through the reaction of dinitrogen pentoxide (N2O5(g)) with chloride-containing surfaces. The importance of ClNO2 in marine and coastal locations is well-recognized due to presence of sea spray aerosol. However, ClNO2 was unexpectedly detected in regions far inland from the ocean, with wintertime levels rivaling marine locations. We tackled investigation of this unresolved chemistry through a series of field-based measurements of atmospheric trace gases, individual particles, and snow, complemented by “lab-in-the-field” experiments and modeling, in wintertime urban environments. Our novel single-particle measurements, combined with online ion chromatography, identified road salt aerosol as the dominant chloride source. ClNO2 production from the reaction of N2O5 with road salt aerosol was quantitatively observed by chemical ionization mass spectrometry. We also exposed road salt-contaminated snow to synthesized N2O5 and observed ClNO2 production, discovering yet another unique chloride source in the wintertime inland environment. We showed that ClNO2 produced from the saline snowpack alters air quality even hundreds of meters above the snow-covered ground. Our discovery of the connection between road salt and wintertime air quality has profound implications for wintertime atmospheric chemistry and decision-making regarding deicing practices, as tens of millions of tons of road salt are spread on roadways for deicing globally each winter.


Kerri Pratt
Building: Chemistry Dow Lab
Event Type: Other
Tags: Biosciences, Chemistry, Science
Source: Happening @ Michigan from Department of Chemistry, Analytical Chemistry