We present a detailed
molecular characterization 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 P flux
can lead to substantial effects on water quality, such as eutrophication,
algal blooms, and oxygen depletion. We aimed to exploit the ultrahigh
resolving power, mass accuracy, and sensitivity of Fourier transform-ion
cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular
composition of an ambient BBOA sample collected downwind of Pacific
Northwest wildfires. The 21-T FT-ICR MS yielded 10 533 distinct
formulae, which included molecular species comprising C, H, O, and
P with or without N, i.e., organophosphorus compounds that have long
been quantified in wildfire smoke but have not yet been characterized
at the molecular level. The lack of detailed molecular characterization
of organophosphorus compounds in BBOA is primarily due to their inherently
low concentrations in aerosols and poor ionization efficiency in complex
mixtures. We demonstrate that the exceptional sensitivity of the 21-T
FT-ICR MS allows qualitative analysis of a previously uncharacterized
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.