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Anion-Catalyzed Dissolution of NO_2 on Aqueous Microdroplets

Yabushita, A. and Enami, S. and Sakamoto, Y. and Kawasaki, M. and Hoffmann, M. R. and Colussi, A. J. (2009) Anion-Catalyzed Dissolution of NO_2 on Aqueous Microdroplets. Journal of Physical Chemistry A, 113 (17). pp. 4844-4848. ISSN 1089-5639.

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Fifty-seven years after NOx (NO + NO_2) were identified as essential components of photochemical smog, atmospheric chemical models fail to correctly predict •OH/HO_2• concentrations under NO_x-rich conditions. This deficiency is due, in part, to the uncertain rates and mechanism for the reactive dissolution of NO_2(g) (2NO_2 + H_2O = NO_3^− + H^+ + HONO) in fog and aerosol droplets. Thus, state-of-the-art models parametrize the uptake of NO_2 by atmospheric aerosol from data obtained on “deactivated tunnel wall residue”. Here, we report experiments in which NO_3^− production on the surface of microdroplets exposed to NO_2(g) for 1 ms is monitored by online thermospray mass spectrometry. NO_2 does not dissolve in deionized water (NO_3^− signals below the detection limit) but readily produces NO_3^− on aqueous NaX (X = Cl, Br, I) microdroplets with NO_2 uptake coefficients γ that vary nonmonotonically with electrolyte concentration and peak at γ_(max) ~ 10^(−4) for [NaX] ~ 1 mM, which is >10^3 larger than that in neat water. Since I^− is partially oxidized to I_2•^− in this process, anions seem to capture NO2(g) into X−NO_2•^− radical anions for further reaction at the air/water interface. By showing that γ is strongly enhanced by electrolytes, these results resolve outstanding discrepancies between previous measurements in neat water versus NaCl-seeded clouds. They also provide a general mechanism for the heterogeneous conversion of NO_2(g) to (NO_3^− + HONO) on the surface of aqueous media.

Item Type:Article
Related URLs:
URLURL TypeDescription
Enami, S.0000-0002-2790-7361
Hoffmann, M. R.0000-0001-6495-1946
Colussi, A. J.0000-0002-3400-4101
Additional Information:Copyright © 2009 American Chemical Society. Received: January 23, 2009; Revised Manuscript Received: March 19, 2009. Publication Date (Web): March 30, 2009. We thank Y. Kanaya for helpful discussions. S.E. is grateful to the JSPS research fellowship for young scientists. This project was supported by the National Science Foundation (ATM-0534990) and a grant-in-aid from the Ministry of Education and Science of Japan. Supporting Information: Additional data, data analysis, and experimental details. This material is available free of charge via the Internet at
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Issue or Number:17
Record Number:CaltechAUTHORS:20090901-105639867
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15520
Deposited By: George Porter
Deposited On:09 Sep 2009 18:41
Last Modified:03 Mar 2020 13:01

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