Organic Nitrogen Ions in Aerosol Mass Spectrometry and Implications for Source Apportionment and Understanding SOA Chemical Processing
JUSTIN TROUSDELL, Christopher Niedek, Weiqi Xu, Yele Sun, Xinlei Ge, Qi Zhang, University of California, Davis
Abstract Number: 213
Working Group: Instrumentation and Methods
Abstract
The identification and utility of organic nitrogen (OrgN) ions detected in the mass spectra of high-resolution aerosol mass spectrometers (HR-AMS) has not been fully explored. Although the AMS spectral features of organic nitrates (ON), a subset of OrgN, have received significant attention, other OrgN fragments are often overlooked due to measurement uncertainties, resulting in lost information. Since the HR-AMS remains the standard instrument for quantitative fine-mode aerosol compositional measurements, it is important to leverage the technology and optimize its analysis potential. A recent study in our lab has demonstrated the possibility of accurately determining OrgN ions using HR-AMS (Ge et al., 2023). Building on this research, we applied positive matrix factorization (PMF) on a combined matrix of the mass spectra of 75 OrgN standards previously collected with the HR-AMS, and thereby correlated CxHyNz+ and CxHyNzOp+ fragments with specific OrgN functional groups. These findings are then interpreted alongside the fitted OrgN ions from ambient datasets. We also conducted PMF only on the OrgN ions (OrgN-PMF) in addition to regular PMF as part of our explorations. Comparing the results between the OrgN-PMF and regular PMF demonstrates that OrgN ions carry important information and can provide additional insight into organic aerosol (OA) sources and processing. The ambient data consistently demonstrated that both primary and secondary OA spectra contain CxHyNz+ and CxHyNzOp+ ions. However, secondary sources are dominated by smaller OrgN fragments (C1-2), whereas primary sources exhibit larger fragments (C3-6). SOA are notably enriched in CH0-4NO+ ions, particularly CHNO+, indicating an enhancement of compounds containing amide (-NH-C(=O)-) functional groups.
Reference
Ge, X., Sun, Y., Trousdell, J., Chen, M., and Zhang, Q.: Enhancing characterization of organic nitrogen components in aerosols and droplets using high-resolution aerosol mass spectrometry, Atmos. Meas. Tech., 17, 423-439, 10.5194/amt-17-423-2024, 2024.