Halogens in the marine environment laboratory investigations of heterogeneous chemistry

Informazioni relative al progetto

ID dell’accordo di sovvenzione: ENV4970394

Progetto chiuso

Data di avvio 1 Ottobre 1997

Data di completamento 31 Marzo 2000

Finanziato da

• Specific programme of research and technological development in the field of environment and climate, 1994-1998

Costo totale Nessun dato

Contributo UE Nessun dato

Coordinato da

MAX-PLANCK-GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V.
Germany

Exploitable results

The kinetics of the heterogeneous reaction of BrONO2, with a solid alkali at ambient temperature. A comparison with the interaction of CIONO2 on NaCL and KBr.

The heterogeneous reactions of Bi-ON02 and CIONO2 with solid alkali halides have been investigated in a Teflon-coated Knudsen flow reactor. at ambient temperature. The initial uptake coefficients of BI-ONO2, on NACI and KBr. substrates are 0.31 and 0.33, respectively. For NaCL substrates BrCI, Br2 and HCI and for- KBr both Br, and HBi. are observed as products. HCI and HBr result from the interaction of NiCl and KBr. respectively, with HNO3 in the hydrolysis of BrON02. Using NACI we observed Br, which is formed from hetci-oaeneotis BRONO, decomposition, which also occurs on solid KBi. samples. Halogen exchange reactions are competing with hydrolysis and decomposition which also take place on non-reactive salts such as NaNO3 and Na,S04. A lilcyli rate of initial uptake (0.2-0.4) and a Br2 yield of the order of 50% are observed on non-reactive salts A,Ith a closed mass balance for- Br2. The CIONO2-,-salt system his been reinvestigated. Experiments on NACI, KBr (reactive salts) and on NaNO3, Na2S04 (non-reactive salts) have BCCTI performed. The hydrolysis of CIONO2, was not observable in contrast to heterogeneous; decomposition which occurred on non reactive salts with a C12 Yield of 25 %. We fitted our uptake experiments using a simple Hinshelwood model with satisfactory results.

The influence of NaBi-/NaCI ratio on the Br- catalysed production of halogenated radicals

The activation of Bi-- and Cl- to atomic Br and Cl in set-sprty aerosol was investigated in smoke chamber experiments. In the presence of 03. hydrocarbons and NACI aerosol alone no activation was observed. B adding, Br- to the aerosol. the chain reaction: Br + 03, > BrO3 BRO+ H02 -> H0Br, H0Br(aq). -> H0Br(acl), H0Br-(aq) + H+ = + Br- ----> Br2, (6). H0Br(aq) + H+ Cl- ----> BrCl (7) was verified. The step from (6) to (7) is accompanied by a decrease of the Br-/C1- from 11600 to less than 112000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with BI-The pH value decreases to less than 2 during. the first minutes of the experiment and lziter on to almost 1 (In the absence of NOx or SO2). This is caused by the formation of oxalic acid from alkanes and toluene. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.