Abstract View
The Role of Hydrates, Competing Chemical Constituents, and Surface Composition on ClNO2 Formation
HALEY ROYER, Dhruv Mitroo, Sarah Hayes, Savannah Haas, Kerri Pratt, Patricia Blackwelder, Thomas Gill, Cassandra Gaston, University of Miami
Abstract Number: 248
Working Group: Aerosol Chemistry
Abstract
Atomic chlorine (Cl*) is a potent oxidizer that can affect air quality. A common source of Cl* is nitryl chloride (ClNO2) that forms when chloride-containing aerosol reacts with dinitrogen pentoxide (N2O5). The formation of ClNO2 presumably occurs only in urban coastal regions where both chloride (Cl-) from sea spray aerosol and N2O5 from anthropogenic activity are abundant. However, recent research has shown that ClNO2 formation also occurs inland, for example when N2O5 reacts with Cl- in saline lakebed (playa) dust. Recent research also has shown that current parameterizations poorly predict ClNO2 formation based on Cl- content from playa dust. To understand this phenomenon, we utilized Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM/EDS), X-Ray Diffraction (XRD), and Single Particle Aerosol Mass Spectrometry (SPAMS) to determine the chemical composition and mineralogy of playa dust from the southwest United States. SEM and SPAMS both revealed the presence of highly hygroscopic Cl-containing minerals (e.g. carnallite) which can deliquesce at low relative humidity (RH), thereby facilitating ClNO2 formation at low RH. XRD revealed the presence of 10Å clay minerals (a mineral category including illite, muscovite, and bioite) in samples with high N2O5 uptakes but low ClNO2 production, suggesting for the first time that clay minerals can outcompete Cl- for N2O5. SPAMS analysis detected high levels of soil organic matter (SOM) in samples with high Cl- content and low N2O5 uptake, suggesting that SOM inhibits N2O5 uptake . Finally, comparisons of ClNO2 yields and Cl- content from bulk and surface analytical techniques indicate that surface analytical techniques predict ClNO2 formation better than bulk analytical techniques, implying that ClNO2 formation occurs on the surface rather than in the bulk aerosol. Our results suggest that current parameterizations for ClNO2 formation must be updated with the additional controlling factors found in this study.