Journal of Atmospheric Chemistry

, Volume 18, Issue 4, pp 359–378 | Cite as

Rate constants for the reactions of the NO3 radical with HCOOH/HCOO and CH3COOH/CH3COO in aqueous solution between 278 and 328 K

  • M. Exner
  • H. Herrmann
  • R. Zellner
Article

Abstract

The kinetics of the aqueous phase reactions of NO3 radicals with HCOOH/HCOO and CH3COOH/CH3COO have been investigated using a laser photolysis/long-path laser absorption technique. NO3 was produced via excimer laser photolysis of peroxodisulfate anions (S2O 8 2− ) at 351 nm followed by the reactions of sulfate radicals (SO 4 ) with excess nitrate. The time-resolved detection of NO3 was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO3 with formic acid (1) and formate (2) rate coefficients ofk1=(3.3±1.0)×105 l mol−1 s−1 andk2=(5.0±0.4)×107 l mol−1 s−1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k1(T)=(3.4±0.3)×1010 exp[−(3400±600)/T] l mol−1 s−1 andk2(T)=(8.2±0.8)×1010 exp[−(2200±700)/T] l mol−1 s−1. The rate coefficients for the reactions of NO3 with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k3=(1.3±0.3)×104 l mol−1 s−1 andk4=(2.3±0.4)×106 l mol−1 s−1. The temperature dependences for these reactions are described by:k3(T)=(4.9±0.5)×109 exp[−(3800±700)/T] l mol−1 s−1 andk4(T)=(1.0±0.2)×1012 exp[−(3800±1200)/T] l mol−1 s−1. The differences in reactivity of the anions HCOO and CH3COO compared to their corresponding acids HCOOH and CH3COOH are explained by the higher reactivity of NO3 in charge transfer processes compared to H atom abstraction. From a comparison of NO3 reactions with various droplets constituents it is concluded that the reaction of NO3 with HCOO may present a dominant loss reaction of NO3 in atmospheric droplets.

Key words

Droplet chemistry acid/base pairs NO3 radicals reaction mechanisms radical reactions pH-dependence 

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Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • M. Exner
    • 1
  • H. Herrmann
    • 1
  • R. Zellner
    • 1
  1. 1.Institut für Physikalische und Theoretische ChemieUniversität GH EssenEssenGermany

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