Fragment ion-functional group relationships in organic aerosols using aerosol mass spectrometry and mid-infrared spectroscopy

Abstract. Aerosol mass spectrometry (AMS) and mid-infrared spectroscopy (MIR) are two analytical methods for characterizing the chemical composition of OM. While AMS provides high-temporal-resolution bulk measurements, the extensive fragmentation during the electron impact (EI) ionization makes the characterization of OM components limited. The analysis of aerosols collected on PTFE filters using MIR, on the other hand, provides functional group (FG) information with reduced sample alteration but results in a relatively low temporal resolution. In this work, we compared and combined MIR and AMS measurements for several environmental chamber experiments to achieve a better understanding of the AMS spectra and the OM chemical evolution by aging. Fresh emissions of wood and coal burning were injected into an environmental simulation chamber and aged with hydroxyl and nitrate radicals. A high-resolution time-of-flight (HR-TOF) AMS measured the bulk chemical composition of fine PM. Fine aerosols were also sampled on PTFE filters before and after aging for the offline MIR analysis. After comparing AMS and MIR bulk measurements, we used multivariate statistics to identify the influential functional groups contributing to AMS OM mass for different aerosol sources and aging processes. We also identified the key mass fragments resulting from each functional group for the complex OM generated from biomass and fossil fuel combustion. Finally, we developed a statistical model that enables estimation of the high-time-resolution functional group composition of OM using collocated AMS and MIR measurements. Using this approach, AMS spectra can be used to interpolate the functional group measurements by MIR, allowing us to better understand the evolution of OM during the aging process.