Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City

Džepina, K.; Volkamer, Rainer; Madronich, S.; Tulet, Pierre; Ulbrich, I. M.; Zhang, Qi; Cappa, Christopher D.; Ziemann, Paul J.; Jiménez, José

doi:10.5194/acp-9-5681-2009

Cited by 266 publications

(386 citation statements)

References 130 publications

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“…Figure 1A summarizes observed ∆OA/∆CO enhancement ratios from different studies that were influenced by urban emissions. Red lines are estimates of emission ratios (POA) (7,12,13,(22)(23)(24)(25); blue lines were obtained in aged air (POA + SOA) (7,9,(17)(18)(19)22). These results were determined from field studies on three continents and indicate that the ∆OA/∆CO ratios in aged urban air are systematically higher.…”

Section: Urban Sourcesmentioning

confidence: 96%

Organic Aerosols in the Earth’s Atmosphere

Gouw

Jimenez²

2009

Environ. Sci. Technol.

389

303

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Organic particles are abundant in the troposphere and important for air quality and climate, but what are their sources?Aerosols, microscopically small particles suspended in air, are an important species in the Earth's atmosphere and influence both air quality and climate. Aerosols are small enough to penetrate deep into the lungs of people and have been linked to severe short-and long-term health effects such as asthma, cardio-respiratory disease, and lung cancer. Aerosols impact the Earth's climate directly through the scattering and absorption of solar radiation, and indirectly through their role as cloud-condensation nuclei. A large fraction (∼50%) of the submicron aerosol mass in the troposphere consists of organic material (1, 2). Direct emissions of organic aerosol (primary organic aerosol or POA) are distinguished from secondary organic aerosol (SOA) formed in the atmosphere from gas-phase precursors. Both POA and the precursors of SOA can be from urban, biogenic, and biomass burning sources. Our understanding of each of these sources is limited at present (3, 4), which hinders the efforts to mitigate the adverse effects. In this feature article, we briefly review the latest insights from field studies into the sources of organic aerosol (OA). Many results were obtained using two relatively new methods for quantifying OA on time scales of minutes: particle-into-liquid sampling combined with total organic carbon analysis for measurements of water-soluble organic carbon (5) and aerosol mass spectrometry (AMS) (6); both have been evaluated in detail against other reported methods, both in terms of the mass loading (7-10) as well as the source apportionment (11-13) of organic aerosol. Urban SourcesGlobal models predict that urban sources of OA are small compared with biomass burning emissions and biogenic SOA formation (4). Nevertheless, several recent studies found that OA was well correlated with tracers of urban pollution such as CO, acetylene (C 2 H 2 ), iso-propylnitrate, and odd oxygen (O 3 + NO 2 ) (8,(14)(15)(16)(17), suggesting that the influence of urban emissions may be larger than previously recognized. These studies showed that the good correlation is not due to emissions of POA, but to a rapid growth of SOA in urban air that overwhelms the direct POA emissions within a few hours of photochemical processing (8,(18)(19)(20).The atmospheric variability in OA is due to the spatial distribution of emissions, transport, chemical transformation, and removal by deposition. By normalizing OA to an inert combustion tracer such as CO or acetylene, the variability due to emissions and transport can be accounted for to a certain extent (8). Enhancement ratios of OA versus CO are denoted as ∆OA/∆CO, where ∆ indicates the excess amount over the background concentration. Accounting for backgrounds is important particularly when using a long-lived species such as CO. In practice, enhancement ratios are often calculated from correlation slopes between OA and CO (7). CO can also be formed from biogenic volatile ...

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Section: Urban Sourcesmentioning

confidence: 96%

Organic Aerosols in the Earth’s Atmosphere

Gouw

Jimenez²

2009

Environ. Sci. Technol.

389

303

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“…Organic aerosols (OA) comprise 20-90% of atmospheric dry particles mass (2), the majority and least understood of which is secondary organic aerosol (SOA), formed from oxidation of gas phase organic vapors in the atmosphere (3)(4)(5)(6). Despite an ongoing intense research effort aimed at understanding the formation and atmospheric evolution of OA, current models severely underestimate the formation of SOA in the atmosphere (5,7).…”

mentioning

confidence: 99%

“…However, when evaporation is considered, their models predict that more than 3∕4 of the SOA mass evaporates upon dilution by a factor of 10, in sharp contrast with measurements. The same study attempted to model measured SOA evaporation in thermodenuder (TD) and concluded that to get better agreement with field measurements requires SOA evaporation coefficients that are 1-3 orders of magnitude below unity (6), which leads to inconsistency with smog chamber SOA formation measurements.…”

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confidence: 99%

“…In their box modeling study of the Mexico City plume, Dzepina et al (6) found that adding precursors and SOA formation mechanisms (9) increases modeled SOA mass, bringing model predictions closer to measurements. However, when evaporation is considered, their models predict that more than 3∕4 of the SOA mass evaporates upon dilution by a factor of 10, in sharp contrast with measurements.…”

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confidence: 99%

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Evaporation kinetics and phase of laboratory and ambient secondary organic aerosol

Vaden

Imre²,

Beránek

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

381

630

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Field measurements of secondary organic aerosol (SOA) find significantly higher mass loads than predicted by models, sparking intense effort focused on finding additional SOA sources but leaving the fundamental assumptions used by models unchallenged. Current air-quality models use absorptive partitioning theory assuming SOA particles are liquid droplets, forming instantaneous reversible equilibrium with gas phase. Further, they ignore the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate. Using accurate and highly sensitive experimental approach for studying evaporation kinetics of size-selected single SOA particles, we characterized room-temperature evaporation kinetics of laboratory-generated α-pinene SOA and ambient atmospheric SOA. We found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models. Adsorption of "spectator" organic vapors during SOA formation, and aging of these coated SOA particles, dramatically reduced the evaporation rate, and in some cases nearly stopped it. Ambient SOA was found to exhibit evaporation behavior very similar to that of laboratory-generated coated and aged SOA. For all cases studied in this work, SOA evaporation behavior is nearly size-independent and does not follow the evaporation kinetics of liquid droplets, in sharp contrast with model assumptions. The findings about SOA phase, evaporation rates, and the importance of spectator gases and aging all indicate that there is need to reformulate the way SOA formation and evaporation are treated by models.single-particle mass spectrometry | morphology A tmospheric particles have a strong, yet poorly characterized effect on climate (1). Organic aerosols (OA) comprise 20-90% of atmospheric dry particles mass (2), the majority and least understood of which is secondary organic aerosol (SOA), formed from oxidation of gas phase organic vapors in the atmosphere (3-6). Despite an ongoing intense research effort aimed at understanding the formation and atmospheric evolution of OA, current models severely underestimate the formation of SOA in the atmosphere (5, 7). The effort to resolve the persistent discrepancy between field measurements and the amount of SOA predicted by atmospheric chemistry models has mostly focused on improving the understanding of SOA formation yields and finding new sources (8-11). In contrast, present models maintain the following fundamental assumptions: (i) Gas-particle partitioning is modeled assuming that all organics form a pseudoideal solution in the condensed particle phase, (ii) SOA particles remain liquid-like throughout their lifetime in the atmosphere, (iii) reversible thermodynamic equilibrium exists between gas and particle phases, and (iv) adsorption of other organic species and their effects on SOA properties and evaporation are ignored.The assumption that particles are liquid is central to ...

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“…Although these indirect methods provide some useful information on the mixing state of POA þ SOA particles, a direct experimental determination of the real morphology of different mixed particles is still required. This type of information would help guide SOA formation models that use empirical fits to laboratory data to calculate yields and partitioning coefficients (4,5,9) and have recently incorporated an option to include or exclude phase separation between POA and SOA phases (10).…”

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confidence: 99%

Morphology of mixed primary and secondary organic particles and the adsorption of spectator organic gases during aerosol formation

Vaden

Song

Zaveri

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

107

146

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Primary organic aerosol (POA) and associated vapors can play an important role in determining the formation and properties of secondary organic aerosol (SOA). If SOA and POA are miscible, POA will significantly enhance SOA formation and some POA vapor will incorporate into SOA particles. When the two are not miscible, condensation of SOA on POA particles forms particles with complex morphology. In addition, POA vapor can adsorb to the surface of SOA particles increasing their mass and affecting their evaporation rates. To gain insight into SOA/POA interactions we present a detailed experimental investigation of the morphologies of SOA particles formed during ozonolysis of α-pinene in the presence of dioctyl phthalate (DOP) particles, serving as a simplified model of hydrophobic POA, using a single-particle mass spectrometer. Ultraviolet laser depth-profiling experiments were used to characterize two different types of mixed SOA/DOP particles: those formed by condensation of the oxidized α-pinene products on size-selected DOP particles and by condensation of DOP on sizeselected α-pinene SOA particles. The results show that the hydrophilic SOA and hydrophobic DOP do not mix but instead form layered phases. In addition, an examination of homogeneously nucleated SOA particles formed in the presence of DOP vapor shows them to have an adsorbed DOP coating layer that is ∼4 nm thick and carries 12% of the particles mass. These results may have implications for SOA formation and behavior in the atmosphere, where numerous organic compounds with various volatilities and different polarities are present.secondary organic aerosol | single-particle mass spectrometry | morphology A nthropogenic aerosol particles in large urban areas are implicated in air quality and health-related problems and are a source of significant uncertainty in our current understanding of climate change at regional and global scales (1). Recent field studies indicate that organic aerosols (OA) constitute anywhere between 20 and 90% of the total dry fine particulate mass (2). Secondary organic aerosol (SOA), generated from the oxidation reaction products of volatile and semivolatile organic compounds (SVOC), is thought to constitute between 64 and 95% of the total OA mass (3). The development of SOA formation models at present represent a major research activity aimed at reconciling the significant differences between field measured SOA concentrations and those predicted by current SOA models in both polluted urban and regional areas (4). Although a number of attempts have been made to explain this discrepancy, none have yet closed the gap between predicted and observed SOA concentrations (4-6).SOA formation can be enhanced in the presence of primary organic aerosols (POA) that serve as additional organic mass to absorb greater amounts of oxidized organic molecules, thus lowering their vapor pressures and increasing SOA formation yields. For POA to absorb SOA, a single well-mixed SOA þ POA phase must form. However, Song et al. (7) found that SOA format...

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Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City

Cited by 266 publications

References 130 publications

Organic Aerosols in the Earth’s Atmosphere

Organic Aerosols in the Earth’s Atmosphere

Evaporation kinetics and phase of laboratory and ambient secondary organic aerosol

Morphology of mixed primary and secondary organic particles and the adsorption of spectator organic gases during aerosol formation

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