PNNL

Abstract

We present a detailed molecular characterisation of organophosphorus compounds in ambient organic aerosol influenced by wildfire smoke. Biomass burning organic aerosol (BBOA) is an important source of phosphorus (P) to surface waters, where even a small imbalance in the flux of P can lead to substantial effects on water quality, such as eutrophication, algal blooms, and oxygen depletion. Our objective here was to exploit the ultrahigh resolving power, mass accuracy, and sensitivity of Fourier transform - Ion Cyclotron Resonance mass spectrometers (FT-ICR MS) to delve deep into the molecular composition of an ambient BBOA sample collected downwind of Pacific Northwest wildfires and that was previously demonstrated to have unprecedented molecular complexity with FT - Orbitrap Elite (FT-OTE) analysis. With its 5-fold higher resolving power as compared to the FTOTE, the 21-Tesla FT-ICR MS yielded a 2-fold greater number of distinct formulae (n = 10,533). It exclusively detected compounds comprising C, H, O, and P with or without N, i.e., organophosphorus compounds, that have long been quantitively reported in wildfire smoke but have not yet been characterised at the molecular level. The lack of detailed molecular characterisation of organophosphorus compounds in BBOA is primarily due to their inherently low concentrations in aerosol and poor ionisation efficiency in complex organic mixtures. We demonstrate that exceptional sensitivity of the 21-T FT-ICR MS allows qualitative analysis of a previously uncharacterised fraction of BBOA without its selective concentration from the organic matrix, exemplifying the need for ultrahigh-resolution tools for a more detailed and accurate molecular depiction of such complex mixtures.