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Factor analysis of combined organic and inorganic aerosol mass spectra from high resolution aerosol mass spectrometer measurements

by Y. L. Sun, Q. Zhang, J. J. Schwab, T. Yang, N. L. Ng, K. L. Demerjian
Atmospheric Chemistry and Physics ()


Positive matrix factorization (PMF) was applied to the merged high\nresolution mass spectra of organic and inorganic aerosols from aerosol\nmass spectrometer (AMS) measurements to investigate the sources and\nevolution processes of submicron aerosols in New York City in summer\n2009. This new approach is able to study the distribution of organic and\ninorganic species in different types of aerosols, the acidity of organic\naerosol (OA) factors, and the fragment ion patterns related to\nphotochemical processing. In this study, PMF analysis of the unified AMS\nspectral matrix resolved 8 factors. The hydrocarbon-like OA (HOA) and\ncooking OA (COA) factors contain negligible amounts of inorganic\nspecies. The two factors that are primarily ammonium sulfate (SO4-OA)\nand ammonium nitrate (NO3-OA), respectively, are overall neutralized.\nAmong all OA factors the organic fraction of SO4-OA shows the highest\ndegree of oxidation (O/C=0.69). Two semi-volatile oxygenated OA (OOA)\nfactors, i.e., a less oxidized (LO-OOA) and a more oxidized (MO-OOA),\nwere also identified. MO-OOA represents local photochemical products\nwith a diurnal profile exhibiting a pronounced noon peak, consistent\nwith those of formaldehyde (HCHO) and O-x(=O-3 + NO2). The NO+/NO2+ ion\nratio in MO-OOA is much higher than that in NO3-OA and in pure ammonium\nnitrate, indicating the formation of organic nitrates. The\nnitrogen-enriched OA (NOA) factor contains similar to 25% of acidic\ninorganic salts, suggesting the formation of secondary OA via acid-base\nreactions of amines. The size distributions of OA factors derived from\nthe size-resolved mass spectra show distinct diurnal evolving behaviors\nbut overall a progressing evolution from smaller to larger particle mode\nas the oxidation degree of OA increases. Our results demonstrate that\nPMF analysis of the unified aerosol mass spectral matrix which contains\nboth inorganic and organic aerosol signals may enable the deconvolution\nof more OA factors and gain more insights into the sources, processes,\nand chemical characteristics of OA in the atmosphere.

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