Effect of hydrophilic organic seed aerosols on secondary organic aerosol formation from ozonolysis of α-pinene.

Atmospheric Sciences & Global Change Division, Pacific Northwest National Laboratory, Richland, Washington, USA.
Environmental Science & Technology (Impact Factor: 5.48). 08/2011; 45(17):7323-9. DOI: 10.1021/es201225c
Source: PubMed

ABSTRACT Gas-particle partitioning theory is widely used in atmospheric models to predict organic aerosol loadings. This theory predicts that secondary organic aerosol (SOA) yield of an oxidized volatile organic compound product will increase as the mass loading of preexisting organic aerosol increases. In a previous work, we showed that the presence of model hydrophobic primary organic aerosol (POA) had no detectable effect on the SOA yields from ozonolysis of α-pinene, suggesting that the condensing SOA compounds form a separate phase from the preexisting POA. However, a substantial faction of atmospheric aerosol is composed of polar, hydrophilic organic compounds. In this work, we investigate the effects of model hydrophilic organic aerosol (OA) species such as fulvic acid, adipic acid, and citric acid on the gas-particle partitioning of SOA from α-pinene ozonolysis. The results show that only citric acid seed significantly enhances the absorption of α-pinene SOA into the particle-phase. The other two seed particles have a negligible effect on the α-pinene SOA yields, suggesting that α-pinene SOA forms a well-mixed organic aerosol phase with citric acid and a separate phase with adipic acid and fulvic acid. This finding highlights the need to improve the thermodynamics treatment of organics in current aerosol models that simply lump all hydrophilic organic species into a single phase, thereby potentially introducing an erroneous sensitivity of SOA mass to emitted OA species.

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    ABSTRACT: Organic compounds are known to comprise a significant fraction of the atmospheric aerosol population and have been found to contribute to the concentration of cloud condensation nuclei (CCN). Much of this organic material is secondary in nature; secondary organic aerosol (SOA) is formed when volatile organic compounds are oxidized to form less volatile products, which then condense into the aerosol phase. Many organic compounds found in the atmosphere, of both anthropogenic and biogenic origin, have been found to produce SOA. Such reactions typically result in complex mixtures of products, only a fraction of which have been identified. Thus while there have been several studies exploring the potential for organic particles to act as CCN (including some of the compounds identified in SOA products), there have been almost no direct investigation of the potential CCN activity of SOA. This paper presents the results of a series of experiments measuring directly the CCN activity of SOA produced by the ozonolysis of several common biogenic compounds. Six compounds were studied: five monoterpenes (α -pinene, β -pinene, Δ 3-carene, limonene, terpinolene) and one terpinoid alcohol (terpinen-4-ol). The chosen monoterpenes represent an estimated 87% of global monoterpene emissions, while the terpenoid alcohols make up approximately 25% of the other biogenic compounds capable of forming SOA. In each experiment, SOA was generated under controlled conditions at the Caltech indoor facility. Over several hours, CCN concentrations were measured at supersaturations ranging from 0.27% to 0.80%. These data are compared to simultaneous particle concentration and size distribution observations to determine the relationship between particle diameter and CCN activity. The analysis indicates considerable variation in CCN activity among the experiments; possible causes for such variability are explored.
    Journal of Geophysical Research Atmospheres 12/2004; · 3.44 Impact Factor
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    Journal of Geophysical Research Atmospheres 01/2002; 107. · 3.44 Impact Factor
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    ABSTRACT: Semi-empirical secondary organic aerosol (SOA) models typically assume a well-mixed organic aerosol phase even in the presence of hydrophobic primary organic aerosols (POA). This assumption significantly enhances the modeled SOA yields as additional organic mass is made available to absorb greater amounts of oxidized secondary organic gases than otherwise. We investigate the applicability of this critical assumption by measuring SOA yields from ozonolysis of α-pinene (a major biogenic SOA precursor) in a smog chamber in the absence and in the presence of dioctyl phthalate (DOP) and lubricating oil seed aerosol. These particles serve as surrogates for urban hydrophobic POA. The results show that these POA did not enhance the SOA yields. If these results are found to apply to other biogenic SOA precursors, then the semi-empirical models used in many global models would predict significantly less biogenic SOA mass and display reduced sensitivity to anthropogenic POA emissions than previously thought.
    Geophysical Research Letters 06/2007; 34(20). · 3.98 Impact Factor