Carbonate (CO3 2-) and sulfate (SO4 2-) species are reactive inorganic components of the fine particulate matter (PM) implicated in several environmental and human health issues. Sulfate aerosols usually arise from the atmospheric oxidation of SO2, contributing to acid rain and climate change. [1] In this study the reactivity of [(Na2CO3)n NaCO3]- cluster ions (n≥1) was probed towards SO2 and 13CO2, as a model of processes occurring at the liquid/gas phase interface. The experiments were performed on a LTQ XL linear ion trap (Thermo Fisher Scientific) equipped with an electrospray ionization (ESI) source in negative ion mode. The instrument was in-house modified [2] to allow the introduction of neutral reagent gases (SO2, 13CO2) into the ion trap and measure the kinetic rate constants of the observed ion-molecule reactions. [(Na2CO3)n NaCO3]- cluster ions were generated by spraying a 10^-3 M solution of Na2CO3 in H2O/CH3CN 1:3. Cluster ions with the general formula [(Na2CO3)n NaCO3]- were observed in the gas-phase with n≥1. In the presence of SO2 these carbonate species were quantitatively converted into the corresponding sulfite cluster ions [(Na2SO3)n NaSO3]- through a sequential replacement of each CO2 moiety with a SO2 molecule. The SO2→CO2 conversion may occur through the direct transfer of O 2- from CO3 2- to a SO2 molecule, as reported in a previous study identifying the reactions of SO2 at the surface of a molten carbonate eutectic. [3] The rate constants related to the SO2 adsorption and CO2 release were measured by monitoring the signal of the selected carbonate cluster ion as a function of SO2 concentration. The obtained values were investigated on the basis of n. All the reactions are very fast and efficient. The same experiments were performed also in the presence of 13CO2. As in the case of SO2, 13CO2 is incorporated into the cluster ion structures by replacing CO2 and leading to [(Na2 13CO3)n Na 13CO3]- ions with rate constants lower than those obtained for SO2. SO2 molecules were converted into gaseous CO2 via the reaction of carbonate cluster ions and the consequent formation of sulfite cluster species. Although varying the number n of (Na2CO3) moiety of the reactant ion, CO2 is always efficiently replaced and SO2 entrapped. The same reactions were observed also in the presence of labeled 13CO2, but showing rate constants lower than those measured for SO2. A liquid/gas phase model has been reported to describe the processes involved in the maintenance of the atmospheric SO2/CO2 balance or in the SO2 removal from flue gases.
Sulfur dioxide uptake by sodium carbonate cluster anions in the gas phase / Salvitti, Chiara; Troiani, Anna; de Petris, Giulia. - unico:(2018), pp. 955-956. (Intervento presentato al convegno XXII international mass spectrometry conference tenutosi a Florence; Italy).
Sulfur dioxide uptake by sodium carbonate cluster anions in the gas phase
Salvitti, Chiara
;Troiani, Anna;de Petris, Giulia
2018
Abstract
Carbonate (CO3 2-) and sulfate (SO4 2-) species are reactive inorganic components of the fine particulate matter (PM) implicated in several environmental and human health issues. Sulfate aerosols usually arise from the atmospheric oxidation of SO2, contributing to acid rain and climate change. [1] In this study the reactivity of [(Na2CO3)n NaCO3]- cluster ions (n≥1) was probed towards SO2 and 13CO2, as a model of processes occurring at the liquid/gas phase interface. The experiments were performed on a LTQ XL linear ion trap (Thermo Fisher Scientific) equipped with an electrospray ionization (ESI) source in negative ion mode. The instrument was in-house modified [2] to allow the introduction of neutral reagent gases (SO2, 13CO2) into the ion trap and measure the kinetic rate constants of the observed ion-molecule reactions. [(Na2CO3)n NaCO3]- cluster ions were generated by spraying a 10^-3 M solution of Na2CO3 in H2O/CH3CN 1:3. Cluster ions with the general formula [(Na2CO3)n NaCO3]- were observed in the gas-phase with n≥1. In the presence of SO2 these carbonate species were quantitatively converted into the corresponding sulfite cluster ions [(Na2SO3)n NaSO3]- through a sequential replacement of each CO2 moiety with a SO2 molecule. The SO2→CO2 conversion may occur through the direct transfer of O 2- from CO3 2- to a SO2 molecule, as reported in a previous study identifying the reactions of SO2 at the surface of a molten carbonate eutectic. [3] The rate constants related to the SO2 adsorption and CO2 release were measured by monitoring the signal of the selected carbonate cluster ion as a function of SO2 concentration. The obtained values were investigated on the basis of n. All the reactions are very fast and efficient. The same experiments were performed also in the presence of 13CO2. As in the case of SO2, 13CO2 is incorporated into the cluster ion structures by replacing CO2 and leading to [(Na2 13CO3)n Na 13CO3]- ions with rate constants lower than those obtained for SO2. SO2 molecules were converted into gaseous CO2 via the reaction of carbonate cluster ions and the consequent formation of sulfite cluster species. Although varying the number n of (Na2CO3) moiety of the reactant ion, CO2 is always efficiently replaced and SO2 entrapped. The same reactions were observed also in the presence of labeled 13CO2, but showing rate constants lower than those measured for SO2. A liquid/gas phase model has been reported to describe the processes involved in the maintenance of the atmospheric SO2/CO2 balance or in the SO2 removal from flue gases.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
