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The fuel of atmospheric chemistry: Toward a complete description of reactive organic carbon

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Science Advances  05 Feb 2020:
Vol. 6, no. 6, eaay8967
DOI: 10.1126/sciadv.aay8967
  • Fig. 1 The sources of key reactive emissions into the atmosphere that lead to secondary products of interest for air quality and climate.

    Bottom: Emission sectors generate a range of reactive chemical species: sulfur dioxide (SO2), dimethyl sulfide (DMS), nitrogen oxides (NOx), ammonia (NH3), reactive organic carbon (ROC), carbon monoxide (CO), and methane (CH4). (Given that DMS is a major contributor to the sulfur budget, but a minor component of the ROC budget, we treat it separately here.) Relative global emissions of each are shown on the right (a). Middle (b): The relative contribution of each component to total atmospheric oxidation, estimated from OH reactivity. Top (c): Relative contribution of each species to the global atmospheric burden of secondary PM2.5, tropospheric O3, and secondary CO2. The gray arrow denotes that tropospheric ozone production is catalyzed by NOx. Note that the secondary CO2 source shown here is equivalent to ~10% of the global CO2 emissions from fossil fuels. In all cases—emissions, oxidation, and formation of secondary species—ROC (shown in green throughout) is a major, if not dominant, contributor, highlighting its central importance in tropospheric chemistry. See the Supplementary Materials for a detailed description of methods and sources (31, 58, 68, 69) used to estimate these values.

  • Fig. 2 Simplified atmospheric life cycle of ROC.

    ROC is emitted into the atmosphere from both biogenic and anthropogenic sources, typically as complex mixtures of reduced molecules. Atmospheric oxidation leads to the formation of a large number of secondary ROC species (some of which keep the carbon skeleton intact; others break it apart). This increase in chemical complexity is likely magnified as oxidation continues over multiple generations.

  • Fig. 3 Illustrative timeline of the advances in the online (real-time or near–real-time) measurement of ambient ROC mass over the last decades.

    Colored bars are qualitative estimates of measurable carbon (aerosol in green, gases in blue) as a function of volatility; dashed lines denote the amount of ROC in each bin that is measurable using current (2019) instrumentation. Solid outlines indicate the fraction of carbon that is measured as individual species rather than as unresolved mixtures. Dates correspond to the approximate timing that a given measurement approach was adopted for measuring atmospheric ROC. The major developments in analytical techniques depicted in this timeline (9, 3436, 7083) are given in the Supplementary Materials; see (33) for a comprehensive review of modern analytical approaches.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/6/eaay8967/DC1

    Section S1. Methodology for estimating values in Fig. 1

    Section S2. Methodology for estimating values in Fig. 3

    Table S1. Global annual emissions total shown in Fig. 1(a).

    Table S2. Global annual mean estimated tropospheric OH reactivity shown in Fig. 1(b).

    Table S3. Global annual mean burden of secondary PM shown in Fig. 1(c).

    Table S4. Contribution to tropospheric ozone burden shown in Fig. 1(c).

    Table S5. Sources of secondary CO2 production shown in Fig. 1(c).

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Methodology for estimating values in Fig. 1
    • Section S2. Methodology for estimating values in Fig. 3
    • Table S1. Global annual emissions total shown in Fig. 1(a).
    • Table S2. Global annual mean estimated tropospheric OH reactivity shown in Fig. 1(b).
    • Table S3. Global annual mean burden of secondary PM shown in Fig. 1(c).
    • Table S4. Contribution to tropospheric ozone burden shown in Fig. 1(c).
    • Table S5. Sources of secondary CO2 production shown in Fig. 1(c).

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