A model of energy-dependent agglomeration of hydrocarbon aerosol particles and implication to titan’s aerosols

Dimitrov, Vasili; Bar‐Nun, A.

doi:10.1016/s0021-8502(98)00016-0

Cited by 19 publications

(21 citation statements)

References 20 publications

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“…The model behavior is again consistent with the observations. Therefore, the simultaneous reproduction of multiple Cassini observations by our simulation provides strong evidence for the production and growth of aerosol particles in Titan's ionosphere and supports previous theoretical and laboratory studies suggesting that the aerosol is produced in the upper atmosphere (11,13,14,(35)(36)(37)(38).…”

Section: Lessons From Titansupporting

confidence: 84%

Aerosol growth in Titan’s ionosphere

Lavvas

Yelle

Koskinen

et al. 2013

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

139

134

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Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan's upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere.planetary sciences | heterogeneous chemistry | particles charging | plasma P hotochemical aerosols are observed in many atmospheres of our solar system (1-3), and their presence is also detected in exoplanet atmospheres (4). Apart from their direct influence on the atmospheric properties through their interaction with the radiation field, aerosols have further astrobiological implications; their presence in the early Earth's atmosphere could have protected the surface and any life evolving there from UV radiation (5), and laboratory studies of Titan aerosol analogs have identified an in vitro formation of amino acids during aerosol production (6). However, the general mechanisms involved in the production and growth of photochemical aerosols from atmospheric gases have remained elusive. Titan, as the most extreme example of an aerosol-dominated atmosphere, provides a unique opportunity to investigate these mechanisms.Cassini observations revealed the presence of aerosols in multiple regions of the atmosphere, from the troposphere (7), stratosphere (8), and mesosphere (9, 10) up to the thermosphere where the detection of large mass positive and particularly negative ions has been suggested to be the signature of aerosol formation (11)(12)(13)(14). During a recent flyby (T70), the Cassini spacecraft penetrated to deeper regions of Titan's thermosphere than usual, reaching altitudes close to 880 km that had not previously been sampled with in situ measurements. Measurements from the Langmuir probe (LP) during this unique flyby reveal a high abundance of negative ions at closest approach, comparable to the positive ion density, and a corresponding decrease in the electron density (15). This conclusion is supported by the analysis of multiple Cassini observations, which reveals that the observed electron density is smaller than the density anticipated from photochemical equilibrium, implying that the photochemical models are missing a significant electron loss mechanism (16, 17). Thus, current observations demonstrate a significant decrease of the electron density relative to the positive ion density in the lower ionosphere with a concurrent increase in the density of the negative ions.Aerosols, or dust particles in general, are known to interact with free electr...

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Section: Lessons From Titansupporting

confidence: 84%

Aerosol growth in Titan’s ionosphere

Lavvas

Yelle

Koskinen

et al. 2013

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

139

134

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“…Furthermore, the limit of the coating process is quite close to the lower boundary of the region characterized by a steep decrease (480 vs. 470 km). Thus, coating of the haze particles by condensable aliphatics such as heavy alkanes, as described by Dimitrov & Bar-Nun (1999), may explain the further decrease of η from 480 to 450 km, and also between 350 and 250 km.…”

Section: Discussionmentioning

confidence: 91%

“…While the aromatic rings remain the same, the polyvinyls lose their aromatic-like structure by cross-linking (Jacovi et al 2010;Dimitrov & Bar-Nun 2003). Another process occurs around 480 km and below: the coating of the aerosols by the available aliphatic condensable gases in the atmosphere such as methane, ethane, propane, and heavier alkanes (Dimitrov & Bar-Nun 1999). Some ethylene, acetylene, and nitriles are also present, but far fewer than methane and ethane.…”

Section: Discussionmentioning

confidence: 99%

“…The core material itself, composed of refractory organics, appears to be preserved down to the surface. On the other hand, theoretical modeling of the physicochemical processes that lead to the formation of the haze particles in Titan's upper atmosphere provides another avenue for deciphering their nature (Podolak et al 1984;Bar-Nun et al 1988;Dimitrov & Bar-Nun 1999). In particular, Dimitrov & Bar-Nun (1999) proposed a model of an energy-dependent agglomeration of hydrocarbon aerosol particles in Titan's atmosphere, and several of the particle properties predicted by their model have been confirmed by the DISR results (Bar-Nun et al 2008).…”

Section: Introductionmentioning

confidence: 93%

“…On the other hand, theoretical modeling of the physicochemical processes that lead to the formation of the haze particles in Titan's upper atmosphere provides another avenue for deciphering their nature (Podolak et al 1984;Bar-Nun et al 1988;Dimitrov & Bar-Nun 1999). In particular, Dimitrov & Bar-Nun (1999) proposed a model of an energy-dependent agglomeration of hydrocarbon aerosol particles in Titan's atmosphere, and several of the particle properties predicted by their model have been confirmed by the DISR results (Bar-Nun et al 2008). On that basis, Dimitrov & Bar-Nun (2002, 2003 investigated the possible aging or hardening of the haze particles and proposed that there might be a region of major change in the haze properties around 570 or 620 km altitude, depending on the type of aging, either spontaneous or forced: above this level, the haze particles are fine and sticky, containing a large proportion of double-bond C=C; below this, the particles become less sticky and completely aged or hardened, with a smaller proportion of double bonds.…”

Section: Introductionmentioning

confidence: 99%

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Three-micron extinction of the Titan haze in the 250–700 km altitude range: Possible evidence of a particle-aging process

Courtin¹,

Kim²,

Bar‐Nun³

2014

A&A

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Context. The chemical nature of the Titan haze is poorly understood. The investigation carried out by the Cassini-Huygens suite of instruments is bringing new insights into this question. Aims. This work aims at deriving the vertical variation of the spectral structure of the 3.3-3.4 μm absorption feature of the Titan haze from Cassini VIMS solar occultation data recorded between 250 and 700 km altitude. Methods. We computed the transmittance of Titan's atmosphere using a spherical shell model and a radiative transfer code including the influence of CH 4 , CH 3 D, and C 2 H 6 , as well as the effects of absorption and scattering by the haze particles. We derived the haze extinction from a comparison of the synthetic spectra with the VIMS solar occultation spectra. Results. We find a marked change in the relative amplitudes of the 3.33 and 3.38 μm features, which are characteristic of aromatic (double C=C chains or rings) or aliphatic (single C-C chains) structural groups, respectively. The pseudo-ratio of aromatics to aliphatics (uncorrected for the absolute band strengths) varies from 3.3 ± 1.9 at 580−700 km to 0.9 ± 0.1 at 350−450 km, and is 0.5 ± 0.1 around 250 km. The structural change from the aromatic to the aliphatic type between 580 and 480 km appears to correspond to a spontaneous aging of the particles -a transition between unannealed and hardened particles -while the further decrease of the pseudo-ratio of aromatics to aliphatics below 480 km may be related to the coating of the core particles by condensates such as heavy alkanes.

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Aging of Titan's Aerosols

Dimitrov

Bar‐Nun

2002

Icarus

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A model of energy-dependent agglomeration of hydrocarbon aerosol particles and implication to titan’s aerosols

Cited by 19 publications

References 20 publications

Aerosol growth in Titan’s ionosphere

Aerosol growth in Titan’s ionosphere

Three-micron extinction of the Titan haze in the 250–700 km altitude range: Possible evidence of a particle-aging process

Aging of Titan's Aerosols

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