TY - JOUR
T1 - Exploring the atmospheric chemistry of O2SO3- and assessing the maximum turnover number of ion-catalysed H2SO4 formation
AU - Bork, Nicolai Christian
AU - Kurtén, T.
AU - Vehkamäki, H.
PY - 2013/4/4
Y1 - 2013/4/4
N2 - It has recently been demonstrated that the O2SO-3 ion forms in the atmosphere as a natural consequence of ionizing radiation. Here, we present a density functional theorybased study of the reactions of O2SO-3 with O3. The most important reactions are (a) oxidation to O2SO-3 and (b) cluster decomposition into SO3, O2 and O-3. The former reaction is highly exothermic, and the nascent O2SO-3 will rapidly decompose into SO-4 and O2. If the origin of O2SO-3 is SO2 oxidation by O-3, the latter reaction closes a catalytic cycle wherein SO2 is oxidized to SO3. The relative rate between the two major sinks for O2SO-3 is assessed, thereby providing a measure of the maximum turnover number of ion-catalysed SO2 oxidation, i.e. how many SO2 can be oxidized per free electron. The rate ratio between reactions (a) and (b) is significantly altered by the presence or absence of a single water molecule, but reaction (b) is in general much more probable. Although we are unable to assess the overall importance of this cycle in the real atmosphere due to the unknown influence of CO2 and NOx, we roughly estimate that ion-induced catalysis may contribute with several percent of H2SO4 levels in typical CO2-free and low NOx reaction chambers, e.g. the CLOUD chamber at CERN.
AB - It has recently been demonstrated that the O2SO-3 ion forms in the atmosphere as a natural consequence of ionizing radiation. Here, we present a density functional theorybased study of the reactions of O2SO-3 with O3. The most important reactions are (a) oxidation to O2SO-3 and (b) cluster decomposition into SO3, O2 and O-3. The former reaction is highly exothermic, and the nascent O2SO-3 will rapidly decompose into SO-4 and O2. If the origin of O2SO-3 is SO2 oxidation by O-3, the latter reaction closes a catalytic cycle wherein SO2 is oxidized to SO3. The relative rate between the two major sinks for O2SO-3 is assessed, thereby providing a measure of the maximum turnover number of ion-catalysed SO2 oxidation, i.e. how many SO2 can be oxidized per free electron. The rate ratio between reactions (a) and (b) is significantly altered by the presence or absence of a single water molecule, but reaction (b) is in general much more probable. Although we are unable to assess the overall importance of this cycle in the real atmosphere due to the unknown influence of CO2 and NOx, we roughly estimate that ion-induced catalysis may contribute with several percent of H2SO4 levels in typical CO2-free and low NOx reaction chambers, e.g. the CLOUD chamber at CERN.
U2 - 10.5194/acp-13-3695-2013
DO - 10.5194/acp-13-3695-2013
M3 - Journal article
SN - 1680-7316
VL - 13
SP - 3695
EP - 3703
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 7
ER -