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

Y. L. Sun,T. Yang,K. L. Demerjian,J. J. Schwab,Q. Zhang,N. L. Ng

doi:10.5194/acp-12-8537-2012

Abstract

Abstract. Positive matrix factorization (PMF) was applied to the merged high resolution mass spectra of organic and inorganic aerosols from aerosol mass spectrometer (AMS) measurements to investigate the sources and evolution processes of submicron aerosols in New York City in summer 2009. This new approach is able to study the distribution of organic and inorganic species in different types of aerosols, the acidity of organic aerosol (OA) factors, and the fragment ion patterns related to photochemical processing. In this study, PMF analysis of the unified AMS spectral matrix resolved 8 factors. The hydrocarbon-like OA (HOA) and cooking OA (COA) factors contain negligible amounts of inorganic species. The two factors that are primarily ammonium sulfate (SO4-OA) and ammonium nitrate (NO3-OA), respectively, are overall neutralized. Among all OA factors the organic fraction of SO4-OA shows the highest degree of oxidation (O/C = 0.69). Two semi-volatile oxygenated OA (OOA) factors, i.e., a less oxidized (LO-OOA) and a more oxidized (MO-OOA), were also identified. MO-OOA represents local photochemical products with a diurnal profile exhibiting a pronounced noon peak, consistent with those of formaldehyde (HCHO) and Ox(= O3 + NO2). The NO+/NO2+ ion ratio in MO-OOA is much higher than that in NO3-OA and in pure ammonium nitrate, indicating the formation of organic nitrates. The nitrogen-enriched OA (NOA) factor contains ~25% of acidic inorganic salts, suggesting the formation of secondary OA via acid-base reactions of amines. The size distributions of OA factors derived from the size-resolved mass spectra show distinct diurnal evolving behaviors but overall a progressing evolution from smaller to larger particle mode as the oxidation degree of OA increases. Our results demonstrate that PMF analysis of the unified aerosol mass spectral matrix which contains both inorganic and organic aerosol signals may enable the deconvolution of more OA factors and gain more insights into the sources, processes, and chemical characteristics of OA in the atmosphere.

Highlights

Atmospheric fine particles exert a serious impact on air quality and visibility reduction (Watson, 2002), and harmful effects on human health (Pope III et al, 2002, 2009)
Positive matrix factorization (PMF) analysis was performed for the first time to the combined high resolution (HR) mass spectral matrices of organic and inorganic aerosols from the HR-ToF-aerosol mass spectrometer (AMS) measurements conducted at QC in New York City (NYC) in summer 2009
Cooking activities, respectively, an amine-related nitrogen-enriched OA (NOA) that mixes with acidic ammonium sulfate and nitrate from local photochemical production, and three oxygenated OA (OOA) factors, i.e., a LV-OOA likely from further oxidation of OOA, a more oxidized OOA (MO-OOA) and a less oxidized OOA (LOOOA)

Summary

Introduction

Atmospheric fine particles exert a serious impact on air quality and visibility reduction (Watson, 2002), and harmful effects on human health (Pope III et al, 2002, 2009). Organic aerosols (OA) – a major fraction of fine particles (Zhang et al, 2007a; Jimenez et al, 2009) have a highly uncertain impact on radiative forcing (Forster et al, 2007). Current models often underestimate OA loading substantially, mainly due to unknown sources, sinks, and formation mechanisms (e.g., aqueous-phase production of secondary OA) (Heald et al, 2005, 2011; Volkamer et al, 2006; Dzepina et al, 2009; Wood et al, 2010). Sun et al.: Factor analysis of combined organic and inorganic aerosol mass spectra assessing aerosol’s impacts and reducing the uncertainties in models

Methods

Results

Conclusion