Technical Note: Molecular characterization of aerosol-derived water soluble organic carbon using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

A S Wozniak,P G Hatcher,R M Dickhut,J E Bauer,R L Sleighter

doi:10.5194/acp-8-5099-2008

Abstract

Abstract. Despite the acknowledged relevance of aerosol-derived water-soluble organic carbon (WSOC) to climate and biogeochemical cycling, characterization of aerosol WSOC has been limited. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was utilized in this study to provide detailed molecular level characterization of the high molecular weight (HMW; m/z>223) component of aerosol-derived WSOC collected from rural sites in Virginia and New York, USA. More than 3000 peaks were detected by ESI FT-ICR MS within a m/z range of 223–600 for each sample. Approximately 86% (Virginia) and 78% (New York) of these peaks were assigned molecular formulas using only carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) as elemental constituents. H/C and O/C molar ratios were plotted on van Krevelen diagrams and indicated a strong contribution of lignin-like and lipid-like compounds to the aerosol-derived WSOC samples. Approximately 1–4% of the peaks in the aerosol-derived WSOC mass spectra were classified as black carbon (BC) on the basis of double bond equivalents calculated from the assigned molecular formulas. In addition, several high-magnitude peaks in the mass spectra of samples from both sites corresponded to molecular formulas proposed in previous secondary organic aerosol (SOA) laboratory investigations indicating that SOAs are important constituents of the WSOC. Overall, ESI FT-ICR MS provides a level of resolution adequate for detailed compositional and source information of the HMW constituents of aerosol-derived WSOC.

Highlights

The importance of atmospheric aerosols to several areas of environmental study has been well-documented
water-soluble organic carbon (WSOC) accounted for approximately 30% of the OC at both sites, a value near the low end of published WSOC (μg m−3)a (OC/TP)a (BC/OC)b (WSOC/OC) values (Table 1; 20–70%; Krivacsy et al, 2001; Kleefeld et al, 2002; Yang et al, 2004; Decesari et al, 2007)
black carbon (BC) was a minor component of the bulk aerosol carbonaceous material, accounting for only ∼2% of the OC in the Virginia sample and ∼5% of the OC in the New York sample (Table 1)

Summary

Introduction

The importance of atmospheric aerosols to several areas of environmental study has been well-documented. In addition to the general role of aerosols in climate, fossil fuel and biomass combustion produce anthropogenicallyderived aerosols that are known to impair visibility (Charlson, 1969; Jacobson et al, 2000), contribute to ecosystemlevel problems via rain acidification (Likens and Bormann, 1974; Driscoll et al, 2001 and references therein) and the transport and deposition of persistent organic pollutants (Dickhut et al, 2000; Galiulin et al, 2002; Jurado et al, 2004), and cause cardiovascular and respiratory problems in humans (Davidson et al, 2005; Highwood and Kinnersley, 2006). Recent studies estimate that 30–90 Tg yr−1 of aerosol-derived organic carbon

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