Andrew S. Wozniak

Carbon oxidation state as a metric for describing the chemistry of atmospheric organic aerosol

A detailed understanding of the sources, transformations and fates of organic species in the environment is crucial because of the central roles that they play in human health, biogeochemical cycles and the Earths climate. However, such an understanding is hindered by the immense chemical complexity of environmental mixtures of organics; for example, atmospheric organic aerosol consists of at least thousands of individual compounds, all of which likely evolve chemically over their atmospheric lifetimes. Here, we demonstrate the utility of describing organic aerosol (and other complex organic mixtures) in terms of average carbon oxidation state, a quantity that always increases with oxidation, and is readily measured using state-of-the-art analytical techniques. Field and laboratory measurements of the average carbon oxidation state, using several such techniques, constrain the chemical properties of the organics and demonstrate that the formation and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state and carbon number.

Establishing a Measure of Reproducibility of Ultrahigh-Resolution Mass Spectra for Complex Mixtures of Natural Organic Matter

This study describes a method for evaluating the reproducibility of replicate mass spectra acquired for complex natural organic matter (NOM) samples analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, with regard to both peak detection and peak magnitude. Because studies of NOM characterization utilize not only the emergence and disappearance of peaks but also changes in relative peak magnitude, it is important to establish that the differences between samples are significantly larger than those between sample replicates. Here, a method is developed for correcting strict signal-to-noise thresholds, along with a new scheme for assessing the reproducibility of peak magnitudes. Furthermore, a systematic approach for discerning when the comparison of samples by the presence or absence of peaks is appropriate and when it is necessary to compare based on the relative magnitude of the peaks is presented. A variety of 10 different types of NOM samples are analyzed in duplicate or triplicate instrumental injections or experimental extractions. A framework for these procedures is provided, and acceptable reproducibility levels are recommended.

Identifying oil/marine snow associations in mesocosm simulations of the Deepwater Horizon oil spill event using solid-state 13 C NMR spectroscopy

The Deepwater Horizon oil spill stimulated the release of marine snow made up of dead/living plankton/bacteria and their exopolymeric polysaccharide substances (EPS), termed marine oil snow (MOS), promoting rapid removal of oil from the water column into sediments near the well site. Mesocosm simulations showed that Macondo surrogate oil readily associates with the marine snow. Quantitative solid-state 13C NMR readily distinguishes this oil from naturally formed marine snow and reveals that adding the dispersant Corexit enhances the amount of oil associated with the MOS, thus contributing to rapid removal from the water column. Solvent extraction of MOS removes the oil-derived compounds for analysis by one and two-dimensional GC/MS and evaluation of potential transformations they undergo when associated with the EPS. The results reveal that the oil associated with EPS is subjected to rapid transformation, in a matter of days, presumably by bacteria and fungi associated with EPS.

Correction to “Isotopic characterization of aerosol organic carbon components over the eastern United States”

nd 0.22 0.47 0.34 0.29 0.16 0.26 0.24 0.28 WIOC d d 13 C( ‰ )n d � 26.0 � 25.1 � 25.6 � 26.7 � 26.8 � 24.2 � 25.9 � 25.8 D 14 C( ‰ )n d � 45 42 � 1 � 367 � 461 � 231 � 353 � 212 fWIOC nd 0.78 0.53 0.66 0.71 0.84 0.74 0.76 0.72 TSE e d 13 C( ‰) � 27.0 nd � 26.2 � 26.6 nd � 27.3 � 28.2 � 27.6 � 27.2 D 14 C( ‰) � 476 nd � 90 � 283 nd � 430 � 119 � 190 � 227 fTSE 0.67 nd 0.90 0.79 nd 0.43 0.74 0.59 0.69 Aliphatic d 13 C( ‰) � 28.6 � 27.7 nd f � 28.2 nd � 27.3 � 28.9 � 28.1 � 28.1 D 14 C( ‰) � 794 � 820 � 961 � 858 nd � 834 � 858 � 846 � 853 faliphatic 0.007 0.001 0.003 0.0039 nd 0.007 0.002 0.004 0.004 Aromatic d 13 C( ‰) � 27.8 � 29.6 � 28.3 � 28.6 � 28.3 � 28.4 � 27.8 � 28.2 � 28.4 D 14 C( ‰) � 692 � 77 � 446 � 405 � 466 � 540 � 446 � 484 � 444 faromatic 0.015 0.009 0.004 0.009 0.009 0.007 0.003 0.007 0.006 Polar d 13 C( ‰) � 27.8 � 26.1 � 28.0 � 27.3 � 28.6 nd � 26.2 � 27.4 � 27.3 D 14 C( ‰) � 750 24 � 93 � 273 � 168 nd � 240 � 204 � 245 fpolar 0.24 0.039 0.25 0.18 0.063 nd 0.066 0.065 0.13 a All reported d 13 C and D 14 C values were corrected for blank contributions following procedures outlined in the text. b ‘nd’ denotes samples for which values were not determined. c Values represent the fraction of TOC accounted for by the parameter of interest (f