Water-Soluble Nitrogen-Containing Organic Compounds in Biomass-Combustion-Derived PM_2.5 Characterized by FT-ICR MS with Multiple Ionization Sources

Nitrogen-containing organic compounds (NOCs) emitted from biomass combustion contribute significantly to air pollution, yet their comprehensive characterization remains limited. In this study, NOCs in PM2.5 derived from combustion of pine wood and wheat straw were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with six ionization modes, including electrospray ionization positive (+ESI) and negative (−ESI) modes, matrix-assisted laser desorption/ionization positive (+MALDI) and negative (−MALDI) modes, atmospheric-pressure photoionization positive mode (+APPI), and atmospheric-pressure chemical ionization positive mode (+APCI). This study marks the first application of FT-ICR MS with six ionization modes for biomass-combustion-derived PM2.5 characterization. We have successfully established a more comprehensive formula inventory for CHON molecules, including 7486 from pine wood combustion and 8341 from wheat straw combustion. These represent increases of 55.4–717% and 42.3–424%, respectively, compared to the numbers of formulas detected by the individual ionization modes. Furthermore, NOCs with varying oxidation states and volatilities exhibit distinct detection performance across the six ionization modes, offering deeper insights into their characteristics and enhancing the data support for the interpretation of atmospheric chemical processes.