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 Earth's 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.

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Figure 1: Possible combinations of average carbon oxidation state () and number of carbon atoms (nC) for stable organic molecules.
Figure 2: Location in nC space of organic aerosol, based upon measurements of organic aerosol.
Figure 3: Chemical complexity of organics as a function of oxidation state and carbon number.
Figure 4: Oxidation trajectories in nC space, as determined from laboratory studies of oxidation reactions.


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This work was supported by the US Environmental Protection Agency (EPA) Science To Achieve Results (STAR) program (grant R833746 to J.H.K., N.M.D., D.R.W.), the US Department of Energy (DOE: grant DE-FG02-05ER63995), the National Science Foundation (NSF: grant ATM-0904292 to C.E.K., D.R.W. and M.R.C.; grants ATM-0449815 and ATM-0919189 to J.L.J.) and the National Oceanic and Atmospheric Administration (NOAA: grant NA08OAR4310565). K.R.W., H.B., E.R.M. and J.D.S are supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, and Chemical Sciences Division of the US DOE (contract no. DE-AC02-05CH11231), with additional support from the Laboratory Directed Research and Development Program at the Lawrence Berkeley National Laboratory (LBNL). J.D.S. was also supported by the Camille and Henry Dreyfus foundation postdoctoral program in environmental chemistry. This paper has not been subject to peer and policy review by the above agencies, and therefore does not necessarily reflect their views; no official endorsement should be inferred.

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The present work was originally conceived by J.H.K. with C.E.K. and D.R.W., with substantial input by N.M.D., J.L.J., M.R.C., S.H.K. and K.R.W. The ESI data were provided by K.E.A., L.R.M. and A.S.W. (Table 1 and Fig. 2). S.H.K. carried out the combinatorial calculations to produce Fig. 3. Data on the aging of organics (Fig. 4) were collected by J.D.S., S.H.K., J.H.K. and K.R.W. (squalane, triacontane and levoglucosan) and E.R.M., J.D.S., K.R.W. and H.B. (coronene). J.H.K. wrote the paper with input from all co-authors, especially N.M.D., J.L.J., M.R.C. and C.E.K. The Supplementary Information was written by J.H.K., N.M.D., H.B. and E.R.M.

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Correspondence to Jesse H. Kroll or Erin R. Mysak or Jared D. Smith.

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Kroll, J., Donahue, N., Jimenez, J. et al. Carbon oxidation state as a metric for describing the chemistry of atmospheric organic aerosol. Nature Chem 3, 133–139 (2011).

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