Enhancing characterization of organic nitrogen components in aerosols and droplets using high-resolution aerosol mass spectrometry

Ge, Xinlei; Sun, Yele; Trousdell, Justin; Chen, Mindong; Zhang, Qi

This study aims to enhance the understanding and application of the Aerodyne high-resolution aerosol mass spectrometer (HR-AMS) for the comprehensive characterization of organic nitrogen (inline-formulaON) compounds in aerosol particles and atmospheric droplets. To achieve this goal, we analyzed 75 inline-formulaN-containing organic compounds, representing a diverse range of ambient non-organonitrate ON (NOON) types, including amines, amides, amino acids, inline-formulaN heterocycles, protein, and humic acids. Our results show that NOON compounds can produce significant levels of inline-formula M4inlinescrollmathml chem normal NH x + 24pt14ptsvg-formulamathimg109c69e71ff23ae7ccceca2ac1c708ff amt-17-423-2024-ie00001.svg24pt14ptamt-17-423-2024-ie00001.png and inline-formula M5inlinescrollmathml chem normal NO x + 24pt14ptsvg-formulamathimg028ac11a5d00255f5cd2bebfa53fb902 amt-17-423-2024-ie00002.svg24pt14ptamt-17-423-2024-ie00002.png ion fragments, which are typically recognized as ions representative of inorganic nitrogen species. We also identified the presence of inline-formulaCH2N+ at inline-formula M7inlinescrollmathml m / z 23pt14ptsvg-formulamathimg82359dc0e2bbce7906032009eb1b5089 amt-17-423-2024-ie00003.svg23pt14ptamt-17-423-2024-ie00003.png inline-formula= 28.0187, an ion fragment rarely quantified in ambient datasets due to substantial interference from inline-formula M9inlinescrollmathml chem normal N normal 2 + 16pt15ptsvg-formulamathimg652e67b731236e9e6b59191f38018732 amt-17-423-2024-ie00004.svg16pt15ptamt-17-423-2024-ie00004.png . As a result, the utilization of an updated calibration factor of 0.79 is necessary for accurate NOON quantification via the HR-AMS. We also assessed the relative ionization efficiencies (RIEs) for various NOON species and found that the average RIE for NOON compounds (1.52 inline-formula± 0.58) aligns with the commonly used default value of 1.40 for organic aerosol. Moreover, through a careful examination of the HR-AMS mass spectral features of various NOON types, we propose fingerprint ion series that can aid the NOON speciation analysis. For instance, the presence of inline-formula M11inlinescrollmathml chem normal C n normal H normal 2 n + normal 2 normal N + 56pt14ptsvg-formulamathimgfc2232c7321250cabd8bb3e785ce7f4d amt-17-423-2024-ie00005.svg56pt14ptamt-17-423-2024-ie00005.png ions is closely linked with amines, with inline-formulaCH4N+ indicating primary amines, inline-formulaC2H6N+ suggesting secondary amines, and inline-formulaC3H8N+ representing tertiary amines. inline-formulaCnH2nNO+ ions (especially for inline-formulan values of 1–4) are very likely derived from amides. The co-existence of three ions, inline-formula M17inlinescrollmathml chem normal C normal 2 normal H normal 4 normal NO normal 2 + 50pt15ptsvg-formulamathimg4ff6666caf854b8daca7ecc73fffd2a2 amt-17-423-2024-ie00006.svg50pt15ptamt-17-423-2024-ie00006.png , inline-formulaC2H3NO+, and inline-formulaCH4NO+, serves as an indicator for the presence of amino acids. Additionally, the presence of inline-formula M20inlinescrollmathml chem normal C x normal H y normal N normal 2 + 42pt16ptsvg-formulamathimgcabf41e55f333f84ea7943c3040185a0 amt-17-423-2024-ie00007.svg42pt16ptamt-17-423-2024-ie00007.png ions indicates the occurrence of 2inline-formulaN-heterocyclic compounds. Notably, an elevated abundance of inline-formula M22inlinescrollmathml chem normal NH normal 4 + 24pt15ptsvg-formulamathimg44642da34e3da1fffc83c720c465c894 amt-17-423-2024-ie00008.svg24pt15ptamt-17-423-2024-ie00008.png is a distinct signature for amines and amino acids, as inorganic ammonium salts produce only negligible amounts of inline-formula M23inlinescrollmathml chem normal NH normal 4 + 24pt15ptsvg-formulamathimg7e9bce7dd5b43b642d42082f2f6f1206 amt-17-423-2024-ie00009.svg24pt15ptamt-17-423-2024-ie00009.png in the HR-AMS.

Finally, we quantified the NOON contents in submicron particles (inline-formulaPM1) and fog water in Fresno, California, and inline-formulaPM1 in New York City (NYC). Our results revealed the substantial presence of amino compounds in both Fresno and NYC aerosols, whereas concurrently collected fog water in Fresno contained a broader range of NOON species, including inline-formulaN-containing aromatic heterocycle (e.g., imidazoles) and amides. These findings highlight the significant potential of employing the widespread HR-AMS measurements of ambient aerosols and droplets to enhance our understanding of the sources, transformation processes, and environmental impacts associated with NOON compounds in the atmosphere.

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Ge, Xinlei / Sun, Yele / Trousdell, Justin / et al: Enhancing characterization of organic nitrogen components in aerosols and droplets using high-resolution aerosol mass spectrometry. 2024. Copernicus Publications.

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