A Global Perspective on Aerosol from Low Volatility Organic Compounds

John Seinfeld California Institute of Technology

Category: Aerosol Properties

Working Group: Aerosol Life Cycle

Global organic aerosol is an important component of aerosol direct and indirect climate forcing. Organic aerosol formed from primary semi-volatile and intermediate volatility compounds is estimated in a global chemical transport model. Semi-volatile organic compound (SVOC) (saturation concentrations between about 0.1 and 10^4 ug/m3) oxidation is predicted to be a larger global source of net aerosol production than oxidation of traditional parent hydrocarbons (terpenes, isoprene, and aromatics). The yield of aerosol (defined as the ratio of the net mass of aerosol formed to the total mass of the parent hydrocarbon emitted) from SVOCs is about 75% on a global, annually averaged basis. Intermediate volatility compound (IVOC, saturation concentrations between about 10^4 and 10^6 ug/m3) emissions and oxidation are uncertain since they are not typically measured. The use of a naphthalene surrogate with different high-NOx and low-NOx parameterizations produces an aerosol yield of about 30%, or roughly 5 Tg/yr of aerosol from IVOC oxidation. We estimate a total global organic aerosol source between roughly 60 and 100 Tg/yr. This range reflects uncertainty in the parameters for SVOC emission volatility, SVOC oxidation, SVOC emissions, and IVOC emissions, as well as wet deposition. Additional information is needed to constrain the emissions and treatment of SVOCs and IVOCs, which have traditionally not been included in global models. Comparisons to winter organic carbon observations over the U.S. indicate that SVOC emissions are significantly underestimated by the traditional POA inventories. The degree to which IVOC emissions or other parameters are uncertain is not yet established.

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