ISSN:
1573-0662
Keywords:
aerosol
;
atomic bromine
;
atomic chlorine
;
BrCl
;
Br2
;
BrO
;
HOBr
;
oxalic acid
;
pH
;
tropospheric ozone destruction
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
Notes:
Abstract The activation of Br- and Cl- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O3, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br- to the aerosol, the chain reaction: Br + O3 ⇒ BrO, BrO + HO2 ⇒ HOBr, HOBr ⇒ HOBr(aq), HOBr(aq) + H+ + Br- ⇒ Br2 (6), HOBr(aq) + H+ + Cl- ⇒ BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br-/Cl- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NOx or SO2). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br2 by oxalic acid was observed to occur through a two-step mechanism: HC2O4 - + Br2 ↔ Br- + BrC2O4H (k22, k-22), BrC2O4H ⇒ Br- + H+ + 2 CO2 (23) with the following rate constants and ratios of rate constants, k ± 2σ: k22k-23 / k-22 = (2.9 ± 0.3) · 10-4 s-1, k-22 / k-23 = 7000 ± 3000 13000 M-1, k22 = 2 ±-1 4 M-1 s-1, and k-23 〉 0.1 s-1, k-22 〉 600 M-1 s-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1006297819663
