Top PDF Aerosols and Chemistry in the Planetary Atmospheres

Aerosols and Chemistry in the Planetary Atmospheres

Aerosols and Chemistry in the Planetary Atmospheres

Condensation of gas-phase material onto particulate matter is the predominant route by which atmospheric aerosols evolve. The traditional approach to representing formation of secondary organic aerosols (SOAs) is to assume instantaneous partitioning equilibrium of semivolatile organic compounds between gas and particle phases. Growth occurs as the vapor concentration of the species increases owing to gas-phase chemistry. The fundamental mathematical basis of such a condensation growth mechanism (quasi- equilibrium growth) has been lacking. Analytical solutions for the evolution of an organic aerosol size distribution undergoing quasi-equilibrium growth and irreversible diffusion- limited growth are obtained for open and closed systems. The quasi-equilibrium growth emerges as a limiting case for semivolatile species condensation when the rate of change of the ambient vapor concentration is slow compared with the rate of establishment of local gas-aerosol equilibrium. The results suggest that the growth mechanism in a particular situation might be inferred from the characteristics of the evolving size distribution. In certain conditions, a bimodal size distribution can occur during the condensation of a single species on an initially unimodal distribution.
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AerChemMIP: Quantifying the effects of chemistry and aerosols in CMIP6

AerChemMIP: Quantifying the effects of chemistry and aerosols in CMIP6

To guide the diagnostic process, the data request is struc- tured according to overarching analysis subjects. These are detailed in the subsections below: Climate response, Forc- ing, Feedbacks, Chemistry–climate interactions, Air Qual- ity, and Evaluation of model performance. Considerable ex- perience has been gained in previous model intercompari- son exercises (namely CCMVal, CCMI, AeroCom, ACCMIP, and Hemispheric Transport of Air Pollution (HTAP)), but all too often model versions were different from those used in CMIP. AerChemMIP provides a unique opportunity to gener- ate a complete dataset, requested directly from those GCMs providing climate sensitivity and scenario information to CMIP6. A specific problem may be the expected diversity in model complexity, as mentioned in Sect. 3. Models may contain interactive aerosols, tropospheric chemistry, strato- spheric chemistry and any combination of these. AerChem- MIP requests all output unless unavailable from an individual model configuration with good reason.
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Interactions between Tropospheric Chemistry and Aerosols in a Unified GCM Simulation

Interactions between Tropospheric Chemistry and Aerosols in a Unified GCM Simulation

thesis 20110310 0002 Interactions between Tropospheric Chemistry and Aerosols in a Unified GCM Simulation Thesis by Hong Liao In Partial Fulfillment of the Requirements for the Degree of Doctor of Phi[.]

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Simulation of tropospheric chemistry and aerosols with the climate model EC-Earth

Simulation of tropospheric chemistry and aerosols with the climate model EC-Earth

Abstract. We have integrated the atmospheric chemistry and transport model TM5 into the global climate model EC-Earth version 2.4. We present an overview of the TM5 model and the two-way data exchange between TM5 and the IFS model from the European Centre for Medium-Range Weather Forecasts (ECMWF), the atmospheric general cir- culation model of EC-Earth. In this paper we evaluate the simulation of tropospheric chemistry and aerosols in a one- way coupled configuration. We have carried out a decadal simulation for present-day conditions and calculated chem- ical budgets and climatologies of tracer concentrations and aerosol optical depth. For comparison we have also per- formed offline simulations driven by meteorological fields from ECMWF’s ERA-Interim reanalysis and output from the EC-Earth model itself. Compared to the offline simula- tions, the online-coupled system produces more efficient ver- tical mixing in the troposphere, which reflects an improve- ment of the treatment of cumulus convection. The chem- istry in the EC-Earth simulations is affected by the fact that the current version of EC-Earth produces a cold bias with too dry air in large parts of the troposphere. Compared to the ERA-Interim driven simulation, the oxidizing capacity in EC-Earth is lower in the tropics and higher in the extrat- ropics. The atmospheric lifetime of methane in EC-Earth is 9.4 years, which is 7 % longer than the lifetime obtained with ERA-Interim but remains well within the range reported in the literature. We further evaluate the model by comparing the simulated climatologies of surface radon-222 and carbon
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Lidar signal simulation for the evaluation of aerosols in chemistry transport models

Lidar signal simulation for the evaluation of aerosols in chemistry transport models

The complementary active remote-sensing observations of the Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) lidar in space (on board CALIPSO, also part of the A-Train) provide valuable information on the vertical dis- tribution of aerosols (Winker et al., 2009). They were used in several recent studies for the evaluation of chemistry trans- port model (CTM) simulations (e.g. Yu et al., 2010; Ford and Heald, 2012; Ridley et al., 2012). The classic approach for comparing model simulations and satellite observations is using the level 2 (L2) retrievals, which are derived from the Level 1 (L1) observations. The reliability of L2 retrievals is constantly improving (V3 data products have considerably improved compared to the V2 release), and these data have proven to be very useful for analysing aerosol-related pollu- tion events. However, it is a well-documented fact that they are prone to uncertainties (Liu et al., 2009; Omar et al., 2010; Young and Vaughan, 2009; Winker et al., 2009). More specif- ically, the accuracy of these products depends to a large ex- tent on the uncertainties of each step (algorithm) in the pro- cessing chain. A key parameter that is used to derive L2 prod- ucts (backscatter and extinction coefficients) from attenuated backscatter profiles (L1 data) is the extinction-to-backscatter ratio (lidar ratio). The mean values used are based on pre- scribed bi-modal size distributions and characteristic com-
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Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

The Community Earth System Model (CESM) is a com- prehensive model that couples different independent mod- els for atmosphere, land, ocean, sea ice, land ice, and river runoff (e.g., Neale et al., 2013; Lamarque et al., 2012). It can be used in various configurations, depending on the use of different components and the coupling between them. The atmospheric component of CESM, the Community Atmo- sphere Model (CAM), has the capability of including chem- istry of varying complexity. Default CESM configurations used for long-term climate model simulations usually include prescribed chemical fields in the atmosphere using monthly averages. To produce those prescribed input fields, simula- tions with a detailed representation of chemistry and aerosol processes are required. Furthermore, nonlinear interactions between chemistry and aerosols in the atmosphere are impor- tant for chemistry–climate interactions (e.g., Lamarque et al., 2005; Isaksen et al., 2009) or for the simulation of air quality. In CESM version 1.2, CAM version 5 (CAM5), exten- sive tropospheric and stratospheric chemistry, referred here- after to as CAM5-chem, has been successfully implemented. The performance of CAM version 4 (CAM4) with interac- tive chemistry, referred to as CAM4-chem, has been dis- cussed in Lamarque et al. (2012). In this study, a similar setup of both CAM4-chem and CAM5-chem allows for the comparison of both versions and their performance in com- parison to observations. The two atmospheric configurations CAM4-chem and CAM5-chem differ in various aspects, in- cluding the treatment of cloud, convection, turbulent mixing, and aerosol processes (e.g., Neale et al., 2013; Gent et al., 2011; Kay et al., 2012; Liu et al., 2012), whereas the gas- phase chemistry is identical. Resulting differences in dynam- ics, clouds, precipitation, and radiation will alter chemical re- actions in the gas, aqueous, and aerosol phases, and removal processes, and therefore the chemical composition of the at- mosphere in these configurations.
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Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

S. Tilmes et al.: Evaluation of tropospheric chemistry and aerosols in CESM1.2 1423 Acknowledgements. We thank the HIPPO team for performing reliable aircraft observations used in this study, in particular Steven Wofsy for leading the campaigns, Joshua Schwarz and Anne Per- ring or providing black carbon observations, and Ru-Shan Gao for providing ozone observations. We also thank Kenneth Aikin for providing airborne observations in a unified and user-friendly format. MERRA data used in this study have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center through the NASA GES DISC online archive. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the US Department of Energy. The National Center for Atmospheric Research is funded by the National Science Foundation. S. Ghan and P.-L. Ma were supported by the US Department of Energy, Office of Science, Basic Energy Research as part of the Scientific Discoveries through Advanced Computing program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830.
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Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

Description and evaluation of tropospheric chemistry and aerosols in the Community Earth System Model (CESM1.2)

S. Tilmes et al.: Evaluation of tropospheric chemistry and aerosols in CESM1.2 1423 Acknowledgements. We thank the HIPPO team for performing reliable aircraft observations used in this study, in particular Steven Wofsy for leading the campaigns, Joshua Schwarz and Anne Per- ring or providing black carbon observations, and Ru-Shan Gao for providing ozone observations. We also thank Kenneth Aikin for providing airborne observations in a unified and user-friendly format. MERRA data used in this study have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center through the NASA GES DISC online archive. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the US Department of Energy. The National Center for Atmospheric Research is funded by the National Science Foundation. S. Ghan and P.-L. Ma were supported by the US Department of Energy, Office of Science, Basic Energy Research as part of the Scientific Discoveries through Advanced Computing program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830.
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Distributions and regional budgets of aerosols and their precursors simulated with the EMAC chemistry-climate model

Distributions and regional budgets of aerosols and their precursors simulated with the EMAC chemistry-climate model

and thus it is essential to use a global model which provides consistent information within and between different regions. The applied vertical resolution is 31 layers, up to 10 hPa. The model dynamics has been weakly nudged (Jeuken et al., 1996; J¨ockel et al., 2006; Lelieveld et al., 2007) towards the analysis data of the European Centre for Medium- Range Weather Forecasts (ECMWF) operational model (up to 100 hPa) to represent the actual day-to-day meteorology in the troposphere. This allows a direct comparison with observations. The coupling between the radiation and the atmospheric composition has been removed (switched off). This implies that changes in the atmospheric composition calculated by the chemical mechanism (i.e. ozone, aerosols and greenhouse gases) do not induce a dynamical response of the model, which is instead forced by a climatological concentrations of such components. The model output is 5-hourly, thus an entire daily cycle is covered after 5 days. Dry deposition and sedimentation are described extensively in Kerkweg et al. (2006a) (DRYDEP and SEDI submodel) which are based on the big leaf approach. Dry deposition ve- locities depend on physical and chemical properties of the surface cover. Wet deposition is described in Tost et al. (2006a) (SCAV submodel), while its impact on atmospheric composition in the EMAC model is analyzed in detail in Tost et al. (2007a). The emission procedure has been ex- plained by Kerkweg et al. (2006b) (OFFLEM, ONLEM and TNUDGE submodel) and Pozzer et al. (2006) (AIRSEA sub- model). The chemistry is calculated with the MECCA sub- model of Sander et al. (2005). The chemical mechanism is the one used in J¨ockel et al. (2006, see electronic supple- ment), and consists of 104 gas phase species and 245 reac- tions. O 3 related chemistry of the troposphere is included, as well as non-methane-hydrocarbons (NMHCs) decompo- sition (von Kuhlmann at al., 2003). The other submodels used in this study are CONVECT (Tost et al., 2006b), LNOX (Tost et al., 2007b), as well as CLOUD, CVTRANS, JVAL, HETCHEM and TROPOP (J¨ockel et al., 2006).
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Simulating the Impacts of Marine Organic Emissions on Global Atmospheric Chemistry and Aerosols Using an Online Coupled Meteorology and Chemistry Model

Simulating the Impacts of Marine Organic Emissions on Global Atmospheric Chemistry and Aerosols Using an Online Coupled Meteorology and Chemistry Model

http://creativecommons.org/licenses/by/4.0/ Abstract To realistically simulate the impacts of marine isoprene and primary organic aerosols (POA) on atmospheric chemistry, a unified model framework with online emissions, comprehensive treat- ment of gas-phase chemistry, and advanced aerosol microphysics is required. In this work, the global-through-urban WRF/Chem model (GU-WRF/Chem) implemented with the online emissions of marine isoprene and size-resolved marine POA is applied to examine such impacts. The net ef- fect of these emissions was increased surface concentrations of isoprene and organic aerosols and decreased surfaced concentrations of hydroxyl radical and ozone over most marine regions. With the inclusion of these emissions, GU-WRF/Chem better predicted the surface concentrations of isoprene and organic aerosols and the aerosol number size distribution when compared to mea- surements in clean marine conditions.
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CiteSeerX — Atmospheric Chemistry and Physics A new feedback mechanism linking forests, aerosols, and climate

CiteSeerX — Atmospheric Chemistry and Physics A new feedback mechanism linking forests, aerosols, and climate

2000). Under present conditions, increased CO 2 concen- tration will almost linearly increase CO 2 assimilation (Far- quhar and von Caemmerer, 1982), which is likely to lead to increased BVOC emissions as well. The increased con- centrations of BVOCs will then have an important effect on atmospheric chemistry, for example on O 3 formation (Sein- feld and Pandis, 1998), and particularly on the formation and growth of atmospheric aerosols (Kavouras et al., 1998). They will also enhance the condensational growth of small nuclei, and subsequently a larger fraction of aerosol particles will be able to grow to CCN sizes. Because of the uncertain- ties related to the coupling between ambient CO 2 concen- trations and BVOC emissions, we can consider two extreme scenarios: Firstly, assuming that no coupling exists, doubling of atmospheric CO 2 concentration will not affect the global BVOC emission rates at all. Secondly, assuming complete coupling, doubling of atmospheric CO 2 concentration will also double the emission rates. As a moderate estimate, we assume below that the increase in BVOC emissions will be 10%. Note that we ignore the possible increase in BVOC emissions due to increased temperature, lengthened growing season, nitrogen fertilization, or increased leaf area index.
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First implementation of secondary inorganic aerosols in the MOCAGE version R2.15.0 chemistry transport model

First implementation of secondary inorganic aerosols in the MOCAGE version R2.15.0 chemistry transport model

In the implementation, we made choices for representing phenomena favouring computational efficiency over a very detailed representation while keeping a good accuracy. There are weaknesses in this SIA module which could be improved. Firstly, all the microphysical processes have been treated im- plicitly in a very simple way. A next step would be to include them using physical parameterizations, in particular, nucle- ation, condensation and coagulation, which are very impor- tant for the time evolution of the aerosol sizes. Another as- pect to work on is the thermodynamic equilibrium hypoth- esis which leads to uncertainties. To improve this, it is nec- essary to account for the kinetics of the transfer between the gas phase and the aerosol phase, especially for big particles (Wexler and Seinfeld, 1990; Capaldo et al., 2000). A third improvement would be to take into account the formation of secondary organic aerosols in order to have the complete range of atmospheric particles and be able to represent prop- erly the different interactions and impact of aerosols. One of the final goals is to integrate this module for operational fore- casts into the Prev’Air and COPERNICUS programs. The MOCAGE model will also be used to make research studies including long run simulations, for instance, for the CCMI programme (Chemistry–Climate Model initiative) and the analysis of the aerosol budget in the Mediterranean area.
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Modelling multiphase chemistry in deliquescent aerosols and clouds using CAPRAM3.0i

Modelling multiphase chemistry in deliquescent aerosols and clouds using CAPRAM3.0i

Simulations using a non-permanent cloud scenario were carried out for two different environmental conditions focusing on the multiphase chemistry of oxidants and other linked chemical subsystems. Model results were analysed by time-resolved reaction flux analyses allowing advanced interpretations. The model shows significant effects of multiphase chemical interactions on the tropospheric budget of gas-phase oxidants and organic com- pounds. In-cloud gas-phase OH radical concentration reductions of about 90 % and 75 % were modelled for urban and remote conditions, respectively. The reduced in-cloud gas- phase oxidation budget increases the tropospheric residence time of organic trace gases by up to about 30 %. Aqueous-phase oxidations of methylglyoxal and 1,4-butenedial were identified as important OH radical sinks under polluted conditions. The model revealed that the organic C 3 and C 4 chemistry contributes with about 38 %/48 % and 8 %/9 % consid- erably to the urban and remote cloud / aqueous particle OH sinks. Furthermore, the simulations clearly implicate the potential role of deliquescent particles to operate as a reactive chemical medium due to an efficient TMI/HO x,y chemical processing including e.g. an effective in-situ formation of OH radicals. Considerable chemical differences be- tween deliquescent particles and cloud droplets, e.g. a circa 2 times more efficient daytime iron processing in the urban deliquescent particles, were identified. The in-cloud oxidation of methylglyoxal and its oxidation products is identified as efficient sink for NO 3 radicals in the aqueous phase.
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Clouds and Hazes in Planetary Atmospheres

Clouds and Hazes in Planetary Atmospheres

6.6 Discussion We have shown that the existence of a sulfur haze can significantly alter the geomet- ric albedo spectrum of a temperate giant exoplanet. However, our results depend greatly on the properties of the haze, such as the mean particle size and column number density, both of which are determined by microphysical processes, such as nucleation of aerosols, growth by condensation and coagulation, loss through evaporation and collisional breakup, and transport by sedimentation, mixing, and advection (Pruppacher and Klett, 1978). Although the modeling of these processes is beyond the scope of this work and will be treated in a future paper, we can specu- late on how a sulfur haze subject to microphysics di ff er from the simple slab model we have used. A major di ff erence would be the vertical profile of the haze. Vertical mixing will loft sulfur particles to higher altitudes, where the lower atmospheric pressure and S 8 mixing ratio may result in evaporation of haze particles and a de- crease in mean particle size. A haze layer with a vertical gradient in mean particle size would generate a di ff erent geometric albedo spectrum than a layer with the same size distribution at all altitudes.
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Impacts of Cosmic Dust on Planetary Atmospheres and Surfaces

Impacts of Cosmic Dust on Planetary Atmospheres and Surfaces

A recent laboratory study has shown that analogues of silica cores and unablated meteoric material both trigger the nucleation of NAT (James et al. 2017a). The sulfuric acid clouds of Venus are characterized by their high visible albedo (>0.8) and optical thickness (>30), and the nearly total coverage of the planet by their 20 km thick layer. A salient feature of the clouds is the markings or contrasts observed at ultraviolet wavelengths, although the absorber causing these markings has still not been identified. The clouds are essentially a product of atmospheric chemistry, with the photochemical produc- tion of sulfuric acid vapor near the cloud tops functioning as the source for formation of the acid droplets. The ensuing microphysics takes care of the cloud droplet growth through condensation and coagulation, and the droplets are redistributed vertically through sedi- mentation and vertical atmospheric motions, which are particularly vigorous in the lowest, turbulent cloud layers. The three cloud layers are found between 48 and 70 km altitude in the atmosphere, embedded in a haze that surrounds them both above and below.
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A chemical kinetics network for lightning and life in planetary atmospheres

A chemical kinetics network for lightning and life in planetary atmospheres

ABSTRACT There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and  prebiotic chemistry outside the solar system. We present an ion – neutral chemical network constructed from scratch, S TAND 2015, that treats hydrogen, nitrogen, carbon, and oxygen chemistry accurately within a temperature range between 100 and 30,000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. S TAND 2015 is successfully tested against atmospheric chemistry models for HD 209458b, Jupiter, and the present-day Earth using a simple one- dimensional  photochemistry / diffusion code. Our results for the early Earth agree with those of Kasting for CO 2 , H 2 , CO, and O 2 , but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that the  production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.
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Analyses of Planetary Atmospheres Across the Spectrum: From Titan to Exoplanets

Analyses of Planetary Atmospheres Across the Spectrum: From Titan to Exoplanets

and Fortney et al. (2008). Both models assume that the chemistry of these atmospheres is in local thermal equilibrium, and parameterize the unknown recirculation of energy to the night side. We use the Fortney et al. models to explore a range of atmospheric metallicities from 1-1000x solar. Figure 6.3 shows an example of how a change in atmospheric metallicity affects the observed Spitzer 3.6 and 4.5 micron fluxes for WASP-6b. Figure 6.4 shows the comparison of observed data to the 1x and 1000x solar metallicity models for all three planets, with either efficient or inefficient recirculation of atmospheric heating. The relative efficiency of recirculation is implemented by varying the amount of flux incident at the top of the 1-D atmospheric column. For the inefficient case, the incident flux is set equal to the dayside average value, while for the efficient case the incident flux is calculated as the average over the entire surface. The measured eclipse depths for all three planets appear to be consistent with the solar metallicity models, although the relatively high level of 3.6 µm flux from HAT-P-19b is best matched by the 1000x solar model. All three planets also favor atmospheric models with relatively efficient heat recirculation from dayside to nightside, although the difference is only statistically significant for WASP-39b.
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A miniature sensor for electrical field measurements in dusty planetary atmospheres

A miniature sensor for electrical field measurements in dusty planetary atmospheres

Abstract. Dusty phenomena such as regular wind-blown dust, dust storms, and dust devils are the most important, currently active, geological processes on Mars. Electric fields larger than 100 kV/m have been measured in terrestrial dusty phenomena. Theoretical calculations predict that, close to the surface, the bulk electric fields in martian dusty phenomena reach the breakdown value of the isolating properties of thin martian air of about a few 10 kV/m. The fact that martian dusty phenomena are electrically active has important implications for dust lifting and atmospheric chemistry. Electric field sensors are usually grounded and distort the electric fields in their vicinity. Grounded sensors also produce large errors when subject to ion currents or impacts from clouds of charged particles. Moreover, they are incapable of providing information about the direction of the electric field, an important quantity. Finally, typical sensors with more than 10 cm of diameter are not capable of measuring electric fields at distances as small as a few cm from the surface. Measurements this close to the surface are necessary for studies of the effects of electric fields on dust lifting. To overcome these shortcomings, we developed the miniature electric-field sensor described in this article.
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Electrostatic activation of prebiotic chemistry in substellar atmospheres

Electrostatic activation of prebiotic chemistry in substellar atmospheres

Consider a dusty plasma in the atmosphere of a substellar object such as a giant gas exoplanet. The dust particles will be negatively charged and as a result a plasma sheath (an electron depleted region, see Section 3) forms around the particle. As a consequence, the ionic flux at the grain surface increases as the plasma ions are attracted to and are accelerated towards the grain sur- face. Upon reaching the surface the ions have fallen through an electrostatic potential and have been energised. In comparison to the neutral case, the ionic flux is enhanced and the ionic energy amplified, increasing the probability that chemical reactions will occur and that reactions with higher activation ener- gies are accessible. In this way, charged particle surfaces help catalyse chemical reactions otherwise inaccessible at such low-temperatures present in planetary atmospheres.
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Cassini at Titan. The launch of the Cassini probe on 15 TEANBY: PLANETARY ATMOSPHERES

Cassini at Titan. The launch of the Cassini probe on 15 TEANBY: PLANETARY ATMOSPHERES

The enrichment of these gases at high northern latitudes is consistent with subsidence and isola- tion of the north polar atmosphere from the atmosphere at lower latitudes. It is possible that the high winds around the north pole create a polar vortex, which inhibits the mixing of air from inside the vortex with that outside. This may be analogous to the polar vortex that surrounds Antarctica on the Earth, where cold temperatures, and subsiding air from the high atmosphere, leads to the formation of polar stratospheric clouds, which in turn facilitate chlorine production and subsequent ozone depletion. Similar strange chemistry, involving different gases, may happen at Titan’s winter pole. CIRS data already show spectral features of organic compounds that are not detectable at more southern latitudes. More detailed analysis must wait until Cassini observes the north polar region later in the mission.
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