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| - Aerosol Organic-Mass-to-Organic-Carbon Ratio Measurements
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| - The ratio of organic-mass-to-organic-carbon, typicallytaken to be between 1.4 and 1.7, has an uncertainty higherthan 50%, but this value is used in every measurementto date of the organic fraction of atmospheric particles. Arecently developed technique with errors reduced tobetween 9% and 33% provides measurements of this ratiothat show its large variability for samples measured innortheastern Asia and the Caribbean. The technique usesfunctional groups measured by FTIR spectroscopy toestimate composite organic carbon from the number ofcarbon bonds present and organic mass from the molecularmass of each functional group associated with themeasured bond type. The molecular masses associatedwith each functional group are not unique and do not accountfor highly branched organic compositions. For the organicmixtures described by the less than 20% of atmosphericorganic mass that has been speciated by GCMS, thetheoretical discrepancy in the composite organic-mass-to-organic-carbon ratio is less than 5%. The measuredratios for submicron particle samples are skewed: over90% of the measurements collected lie between 1.2 and 1.6,with mean values just below 1.4. This variability highlightsthe importance of measured organic-mass-to-organic-carbon ratios to reduce the uncertainty associated withatmospheric organic aerosol.
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