Decomposition of Clusters of Oxygenated Compounds with NO3– by Applying Voltage Scanning to Chemical Ionization Mass Spectrometry in Steady-State Experiments
Hui Wang, Yarê Baker, Hongru Shen, Rongrong Wu, Sungah Kang, Defeng Zhao, Andreas Wahner, Sören R. Zorn*, and Thomas F. Mentel
Abstract
Oxygenated volatile organic compounds (OVOCs) contribute to atmospheric secondary organic aerosols. To better constrain OVOC distributions, e.g., from the oxidation of phenolics, voltage scanning was applied for the targeted destruction of product nitrate (NO3–) clusters in a chemical ionization mass spectrometer. Herein, the voltage difference at which half of the clusters remain (dV50) represents their bond strength. This study identified the type and relative bond strength of adducts for product distributions that can be observed for hours in our steady-state chamber (SAPHIR*). An unexpected increase was observed in voltage scanning curves of clusters containing nitrated phenols [e.g., C7H7NO3(NO3–)], which was attributed to the declustering of double-analyte clusters [e.g., C14H14N2O6(NO3–)] at small voltage differences. Double-analyte clusters were distinguished from accretion product clusters [e.g., C12H(10,12)Ox(NO3–)] by their significantly lower intermolecular forces. Misidentifying C14H14N2O6 as accretion products could lead to an overestimation of its contribution to particle mass. In addition, the higher bonding strength in C6H(6,8)O4–9(NO3–) compared to that in H2SO4(NO3–) indicates maximum sensitivities of C6H(6,8)O4–9 at the collision limit. We could elucidate the relative acidity of the analytes to HNO3. This study highlights additional dimensions gained from voltage scanning and suggests performing it to clarify the product distribution in complex urban air in the presence of nitrated phenols.