Enhanced Aerosol Source Identification by Utilizing High Molecular Weight Signals in Aerosol Mass Spectra

The aerosol mass spectrometer (AMS) has significantly expanded our understanding of aerosol chemical composition over the past few decades. However, most studies have made limited use of the high molecular weight (HMW) signals in the mass spectra due to their low intensities and multiple overlapping peaks. Using long time-of-flight (LTOF) AMS measurements at a boreal forest site in Finland, we utilize the high resolution of the LTOF and the newly developed binPMF approach to explore the potential of the HMW range to improve source identification. During our measurements, inorganics (primarily sulfate) contributed ∼30% and oxygenated organic aerosol (OOA) contributed ∼60% to aerosol mass. The remaining ∼10% were attributed to specific organic aerosol types: hydrocarbon-like OA (HOA) ∼3%, biomass burning OA (BBOA) ∼0.06%, and a pollution plume from the Kola Peninsula ∼5%. None of these factors were separated using traditional unit-mass resolution PMF (m/z 12–150 Th). The small BBOA factor was only extracted using binPMF on the 100–225 amu m/z range, and using this BBOA temporal profile, we could constrain the BBOA factor for the lower masses, revealing a prominent signal at m/z 60 (a tracer for levoglucosan). We encourage AMS users to experiment with the presented approach with their own datasets.