Laboratory investigations of negative ion molecule reactions of formic and acetic acids: implications for atmospheric measurements by ion-molecule reaction mass spectrometry

Abstract

Laboratory measurements of gas-phase ion-molecule reactions of several negative ion species with formic and acetic acid have been carried out. A flow reactor operating at a temperature of 293 ± 3 K and total gas pressures of either 3 or 9 hPa was used. The negative reagent ion species investigated included OH −, O 2 −, O 3 −, CO 4 −, CO 3 −, CO 3 −H 2O, HCO 3 −H 2O, NO 3 −, NO 3 −H 2O, NO 2 −, and NO 2 −H 2O. The reactions were found to proceed either via proton transfer or clustering. Our measurements of ion-molecule reactions of negative ions with gaseous formic and acetic acids provide a firm base for quantitative detection of these acidic trace gases in the atmosphere by negative ion ion-molecule reaction mass spectrometry.