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: 5.33). 08/2011; 45(17):7323-9. DOI: 10.1021/es201225c
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: Ambient levels of carbonyl compounds and their possible sources, diurnal variations, and personal exposure were investigated in four types of large shopping malls (including department store, supermarket, and bookstore and furniture store) in urban district of Nanchang, China. Eighteen out of the twenty target carbonyls were detected in summer samples while only fifteen carbonyls were detected in winter samples. The descending order of total mean concentration was furniture store (102.2 ± 22.9 µg m−3)>supermarket (84.2 ± 15.7 µg m−3)>department store (79.0 ± 21.1 µg m−3)>book store (68.6 ± 14.5 µg m−3). A significant correlation between the concentration of the low molecular-weight (LMW) carbonyl compounds (5) and ozone was found in summer. The diurnal curve exhibited a higher peak at the morning hour and a lower peak at the evening hour except for acetaldehyde, which peaked at the afternoon hour in winter. The indoor concentrations of LMW carbonyl compounds were found to be higher than their outdoor counterparts with only a few exceptions. For some high molecular weight (HMW) carbonyls (≥C5) especially for benzaldehyde and p-tolualdehyde which might have stronger outdoor source (e.g., vehicle exhaust), had resulting in the Indoor/Outdoor ratios below 1. The personal exposures showed that large shopping malls in Nanchang were important microenvironments for exposure to formaldehyde and acetaldehyde.Analytical Letters 04/2013; 46(6). DOI:10.1080/00032719.2012.747092 · 1.03 Impact Factor
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ABSTRACT: Recent work has established that secondary organic aerosol (SOA) can exist as an amorphous solid, leading to various suggestions that the addition of SOA coatings to existing particles will decrease the reactivity of those particles towards common atmospheric oxidants. Experimental evidence suggests that O3 is unable to physically diffuse through an exterior semi-solid or solid layer thus inhibiting reaction with the core. The extent to which this suppression in reactivity occurs for OH has not been established, nor has this been demonstrated specifically for SOA. Here, measurements of the influence of adding a coating of α-pinene+O3 SOA onto squalane particles on the OH-initiated heterogeneous oxidation rate are reported. The chemical composition of the oxidized internally-mixed particles was monitored on-line using a vacuum ultraviolet-aerosol mass spectrometer. Variations in the squalane oxidation rate with particle composition were quantified by measurement of the effective uptake coefficient, γeff, which is the loss rate of a species relative to the oxidant-particle collision rate. Instead of decreasing, the measured γeff increased continuously as the SOA coating thickness increased, by a factor of ~2 for a SOA coating thickness of 42 nm (corresponding to ca. two thirds of the particle mass). These results indicate that heterogeneous oxidation of ambient aerosol by OH radicals is not inhibited by SOA coatings, and further that condensed phase chemical pathways and rates in organic particles depend importantly on composition.Environmental Science & Technology 02/2014; 48(6). DOI:10.1021/es405177d · 5.33 Impact Factor
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ABSTRACT: Atmospheric ozone-terpene reactions, which form secondary organic aerosol (SOA) particles, can affect indoor air quality when outdoor air mixes with indoor air during ventilation. This study, conducted in Leipzig, Germany, focused on limonene-induced particle formation in a genuine indoor environment (24 m(3)). Particle number, limonene and ozone concentrations were monitored during the whole experimental period. After manual ventilation for 30 min, during which indoor ozone levels reached up to 22.7 ppb, limonene was introduced into the room at concentrations of approximately 180 to 250 μg m(-3). We observed strong particle formation and growth within a diameter range of 9 to 50 nm under real-room conditions. Larger particles with diameters above 100 nm were less affected by limonene introduction. The total particle number concentrations (TPNCs) after limonene introduction clearly exceed outdoor values by a factor of 4.5 to 41 reaching maximum concentrations of up to 267,000 particles cm(-3). The formation strength was influenced by background particles, which attenuated the formation of new SOA with increasing concentration, and by ozone levels, an increase of which by 10 ppb will result in a six times higher TPNC. This study emphasizes indoor environments to be preferred locations for particle formation and growth after ventilation events. As a consequence, SOA formation can produce significantly higher amounts of particles than transported by ventilation into the indoor air.Environmental Science and Pollution Research 05/2015; 22(18). DOI:10.1007/s11356-015-4663-8 · 2.83 Impact Factor
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