83rd Annual

Monday, 10 February 2003
The mechanism of the reaction of the hydroxyl radical (OH) with NaCl
Margaret A. Kaleuati, University of California, Irvine, CA; and B. J. Finlayson-Pitts
Aerosols of both natural and anthropogenic origin are known to exert a large influence on important regional and global scale atmospheric processes. Although sea salt aerosol is one of the most prevalent aerosols worldwide, its reactions that lead to highly reactive chlorine atoms are not well understood. However, these reactions are important since they can impact tropospheric ozone, a toxic air pollutant. A more complete understanding of the mechanisms governing the production and destruction is needed in order to design control strategies, especially in coastal areas where sea salt aerosol is plentiful.

In studies of the reaction of ozone (O3) with aqueous NaCl aerosol in the presence of UV radiation conducted in this laboratory, the gaseous chlorine (Cl2) produced exceeded the quantity predicted by bulk aqueous phase chemistry. A mechanism was proposed to account for the large Cl2 production that was based on the presence of an ion-enhanced air-aerosol interface, as supported by molecular dynamics simulations. Additionally, the chloride ion has a high affinity for scavenging reactive species, such as the hydroxyl radical (OH). The reaction of OH with the surface chloride ion may form a surface complex [(OH. . . .Cl-)interface] that undergoes a self-reaction to form Cl2 and 2 OH-:

[(OH. . . .Cl-)interface] --> Cl2 + 2 OH-.

However, it was not possible to measure OH- in those studies.

We describe here diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies of the reaction of NaCl and OH radicals, formed by irradiation of O3 in the presence of water vapor, to probe for the formation of surface OH-. The proposed mechanism will be reviewed in light of these experiments and the atmospheric implications will be discussed.

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