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Ah-San Wong

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10

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Oleg Yu Vorobyev

Siberian Federal University

Kansas State University

Kathryn LaFevers Evans, Three Eagles

Pacifica Graduate Institute

Cornell University

Rafael Espiritu

De La Salle University

University of Crete

Masaryk University

Richard Gauthier

Santa Rosa Junior College

Dirk K F Meijer

University of Groningen

Macquarie University

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Papers by Ah-San Wong

Radiation Effects in CdZnTe Gamma-Ray Detectors Produced by 199 MeV Protons

Storage and Retrieval for Image and Video Databases, 2000

Many future space missions will use Cadmium Zinc Telluride (CdZnTe) gamma-ray detectors because t... more Many future space missions will use Cadmium Zinc Telluride (CdZnTe) gamma-ray detectors because their operation at room temperature makes compact, lightweight detector systems possible. Even though instruments for space using CdZnTe detectors have already been built, the effect of the high-energy particle space environment on these detectors has not been measured. To determine the effect of energetic charged particles on

Special Paper Oxidant Enhancement in Martian Dust Devils and Storms: Storm Electric Fields and Electron Dissociative Attachment

Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust tran... more Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust transport can generate atmospheric electricity via contact electrification or "triboelectricity." In convective structures such as dust devils and dust storms, grain stratification leads to macro- scopic charge separations and gives rise to an overall electric dipole moment in the aeolian feature, similar in nature to the dipolar electric

Special Paper Oxidant Enhancement in Martian Dust Devils and Storms: Implications for Life and Habitability

We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Ma... more We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Mars. Large-scale electrostatic fields generated by charged sand and dust in the martian dust devils and storms, as well as during normal saltation, can induce chemical changes near and above the surface of Mars. The most dramatic effect is found in the pro- duction of H2O2 whose

Jupiter: Aerosol Chemistry in the Polar Atmosphere

The Astrophysical Journal, 2000

Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the ... more Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the polar region of Jupiter. We develop a new chemical model for aromatic compounds in the Jovian auroral thermosphere/ ionosphere. The model is based on a previous model for hydrocarbon chemistry in the Jovian atmosphere and is constrained by observations from Voyager, Galileo, and the Infrared Space Observatory. Precipitation of energetic electrons provides the major energy source for the production of benzene and other heavier aromatic hydrocarbons. The maximum mixing ratio of benzene in the polar model is , a value that can be compared Ϫ9 2 # 10 with the observed value of in the north polar auroral region. Sufficient quantities of the higher ring ϩ2 Ϫ9 (2) # 10 Ϫ1 species are produced so that their saturated vapor pressures are exceeded. Condensation of these molecules is expected to lead to aerosol formation.

Coupled Clouds and Chemistry of the Giant Planets— A Case for Multiprobes

Space Science Reviews, 2005

In seeking to understand the formation of the giant planets and the origin of their atmospheres, ... more In seeking to understand the formation of the giant planets and the origin of their atmospheres, the heavy element abundance in well-mixed atmosphere is key. However, clouds come in the way. Thus, composition and condensation are intimately intertwined with the mystery of planetary formation and atmospheric origin. Clouds also provide important clues to dynamical processes in the atmosphere. In this chapter we discuss the thermochemical processes that determine the composition, structure, and characteristics of the Jovian clouds. We also discuss the significance of clouds in the big picture of the formation of giant planets and their atmospheres. We recommend multiprobes at all four giant planets in order to break new ground.

Correction to and updated reaction in “Chemical markers of possible hot spots on Mars”

Journal of Geophysical Research, 2005

Although there is no evidence of active volcanism on Mars today, ''localized'' outgassing sources... more Although there is no evidence of active volcanism on Mars today, ''localized'' outgassing sources, the hot spots, may not be ruled out. If outgassing does occur somewhere on Mars, water, carbon dioxide, sulfur species, methane, and to a lesser extent, halogens would be the likely molecules of outgassing, based on terrestrial analogs. The sulfur species, methane, and halogens have not been detected in the Martian atmosphere, but the observations were averaged over large areas, which could result in substantial dilution in abundances. If the interpretation of certain Mars Global Surveyor images indicating recent ground water seepage and surface runoff [Malin and Edgett, 2000] is correct, it may imply that Mars could still be active internally in some places from time to time, and outgassing of the abovementioned species may occur with or without the water seepage. Moreover, if the tentative detection of formaldehyde (CH 2 O) in the equatorial region of Mars [Korablev et al., 1993] is confirmed by future observations, it would imply at least local outgassing of methane, whose oxidation results in the formation of CH 2 O. Considering the possibility of outgassing from some localized hot spots, we have developed a one-dimensional photochemical model that includes methane (CH 4), sulfur dioxide (SO 2), and hydrogen sulfide (H 2 S), starting with their current ''global average'' upper limits of 0.02, 0.1, and 0.1 ppm at the surface, respectively, and then progressively increasing their abundances above possible hot spots. We find that the introduction of methane into the Martian atmosphere results in the formation of mainly formaldehyde, methyl alcohol (CH 3 OH), and ethane (C 2 H 6), whereas the introduction of the sulfur species produces mainly sulfur monoxide (SO) and sulfuric acid (H 2 SO 4). The effect of outgassed halogens on the Martian atmosphere is found to be negligible. Depending upon the flux of outgassed molecules from possible hot spots, some of these species and the resulting new molecules may be detectable locally, either by remote sensing or in situ measurements.

Chemical markers of possible hot spots on Mars

Journal of Geophysical Research, 2003

Correction to “Chemical markers of possible hot spots on Mars”

Journal of Geophysical Research, 2004

Models for Polar Haze Formation in Jupiter's Stratosphere

Icarus, 2002

We present coupled chemical-microphysical models for the formation, growth, and physical properti... more We present coupled chemical-microphysical models for the formation, growth, and physical properties of the jovian polar haze based on a gas-phase photochemical model for the auroral regions developed by A. S. Wong et al. (2000, Astrophys. J. 534, L215-217). In this model, auroral particle precipitation provides an important energy source for enhanced decomposition of methane and production of benzene and polycyclic aromatic hydrocarbons (PAHs). We find that at high altitude, A 4 (pyrene, a hydrocarbon consisting of four fused aromatic rings) should homogeneously nucleate to form tiny primary particles. At lower altitudes, A 3 (phenanthrene) and A 2 (naphthalene) heterogeneously nucleate on the A 4 nuclei. These particles subsequently grow by additional condensation of A 2 on the nucleated particles and by coagulation and eventually sediment out to the troposphere. We run different cases of the aerosol microphysical model for different assumptions regarding the fractal dimension of aggregate particles formed by the coagulation process. If coagulation is assumed to produce spherical particles (of dimensionality 3), then their mean radius at altitudes below the 20-mbar pressure level is computed to be approximately 0.1 µm. If coagulation produces fractal aggregates of dimension 2.1, then their equivalent mean radius below the 20-mbar level is much larger, of order 0.7 µm. Aggregates with fractal dimensions between 2.1 and 3 form with equivalent mean radii between 0.1 and 0.7 µm. In every case, mean particle radius is found to decrease with increasing altitude, as expected for a system approximately in sedimentationcoagulation equilibrium. The predicted range of altitudes where aerosol formation occurs and the mean size to which particles grow are found to be generally consistent with observations. However, our calculations cannot presently account for the large amount of total aerosol loading inferred by M. G. Tomasko et al. (1986, Icarus 65, 218-243). We suggest that the primarily neutral chemical pathway to heavy hydrocarbon and PAH formation proposed by Wong et al. (2000) may proceed too slowly to produce a sufficient amount of condensible material. Inclusion of ion and ion-neutral reactions in the chemical scheme could potentially lead to the prediction of

Evolution of CO on Titan

Icarus, 2002

The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopom... more The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopomers of CO, 13 CO and C 18 O, relative to 12 C 16 O. However, the original isotopic signatures may be altered by photochemical reactions. This paper explains why there is no isotopic enrichment in C in Titan's atmosphere, despite significant enrichment of heavy H, N, and O isotopes. We show that there is a rapid exchange of C atoms between the CH 4 and CO reservoirs, mediated by the reaction 1 CH 2 + * CO → 1 * CH 2 + CO, where * C is 13 C. Based on recent laboratory measurements, we estimate the rate coefficient for this reaction to be 3.2 × 10 −12 cm 3 s −1 at the temperature appropriate for the upper atmosphere of Titan. We investigate the isotopic dilution of CO using the Caltech/JPL one-dimensional photochemical model of Titan. Our model suggests that the time constant for isotopic exchange through the above reaction is about 800 Myr, which is significantly shorter than the age of Titan, and therefore any original isotopic enhancement of 13 C in CO may have been diluted by the exchange process. In addition, a plausible model for the evolution history of CO on Titan after the initial escape is proposed.

Electrical discharges and broadband radio emission by Martian dust devils and dust storms

Geophysical Research Letters, 2003

Triboelectric charging of saltating and colliding sand and dust particles produces strong electri... more Triboelectric charging of saltating and colliding sand and dust particles produces strong electric fields in terrestrial dust devils and dust storms. Acceleration of the charged particles, as well as microdischarges between them, generates wideband electromagnetic radiation. Similar phenomena are expected to be ubiquitous on Mars, because Martian dust devils and dust storms are larger, stronger and more frequent than their terrestrial analogues, and electrical discharges occur at a much lower potential gradient in the thin Martian atmosphere. We present theoretical arguments and observational evidence that Martian dust events produce nonthermal wideband electromagnetic radiation detectable from Earth.

Benzene and Haze Formation in the Polar Atmosphere of Jupiter

Geophysical Research Letters, 2003

Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the... more Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the polar atmosphere, giving rise to intense auroras [Clarke et al., 1996; Grodent et al., 2000]. An important consequence of this energy influx is the production of a dark haze [Pryor and Hord, 1991], the formation mechanism of which was hitherto poorly known. Recent observations of benzene on Jupiter [Bézard et al., 2001; Flasar, 2002] provide new clues for a chemical and aerosol model for the formation of heavy hydrocarbon aerosols. The chemistry begins with the destruction of methane by energetic particles, followed by neutral and ion reactions, ultimately leading to the formation of benzene and other complex hydrocarbons, including multi-ring compounds which subsequently condense. High temperatures and effective eddy mixing engendered by the auroras enhance the formation of heavy hydrocarbons and aerosols. This mechanism may be relevant in the atmospheres of Saturn and extrasolar giant planets, and is an example of how a planetary magnetosphere may influence the chemical composition and climate forcing of the upper atmosphere.

Radiation Effects in CdZnTe Gamma-Ray Detectors Produced by 199 MeV Protons

Storage and Retrieval for Image and Video Databases, 2000

Many future space missions will use Cadmium Zinc Telluride (CdZnTe) gamma-ray detectors because t... more Many future space missions will use Cadmium Zinc Telluride (CdZnTe) gamma-ray detectors because their operation at room temperature makes compact, lightweight detector systems possible. Even though instruments for space using CdZnTe detectors have already been built, the effect of the high-energy particle space environment on these detectors has not been measured. To determine the effect of energetic charged particles on

Special Paper Oxidant Enhancement in Martian Dust Devils and Storms: Storm Electric Fields and Electron Dissociative Attachment

Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust tran... more Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust transport can generate atmospheric electricity via contact electrification or "triboelectricity." In convective structures such as dust devils and dust storms, grain stratification leads to macro- scopic charge separations and gives rise to an overall electric dipole moment in the aeolian feature, similar in nature to the dipolar electric

Special Paper Oxidant Enhancement in Martian Dust Devils and Storms: Implications for Life and Habitability

We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Ma... more We investigate a new mechanism for producing oxidants, especially hydrogen peroxide (H2O2), on Mars. Large-scale electrostatic fields generated by charged sand and dust in the martian dust devils and storms, as well as during normal saltation, can induce chemical changes near and above the surface of Mars. The most dramatic effect is found in the pro- duction of H2O2 whose

Jupiter: Aerosol Chemistry in the Polar Atmosphere

The Astrophysical Journal, 2000

Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the ... more Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the polar region of Jupiter. We develop a new chemical model for aromatic compounds in the Jovian auroral thermosphere/ ionosphere. The model is based on a previous model for hydrocarbon chemistry in the Jovian atmosphere and is constrained by observations from Voyager, Galileo, and the Infrared Space Observatory. Precipitation of energetic electrons provides the major energy source for the production of benzene and other heavier aromatic hydrocarbons. The maximum mixing ratio of benzene in the polar model is , a value that can be compared Ϫ9 2 # 10 with the observed value of in the north polar auroral region. Sufficient quantities of the higher ring ϩ2 Ϫ9 (2) # 10 Ϫ1 species are produced so that their saturated vapor pressures are exceeded. Condensation of these molecules is expected to lead to aerosol formation.

Coupled Clouds and Chemistry of the Giant Planets— A Case for Multiprobes

Space Science Reviews, 2005

In seeking to understand the formation of the giant planets and the origin of their atmospheres, ... more In seeking to understand the formation of the giant planets and the origin of their atmospheres, the heavy element abundance in well-mixed atmosphere is key. However, clouds come in the way. Thus, composition and condensation are intimately intertwined with the mystery of planetary formation and atmospheric origin. Clouds also provide important clues to dynamical processes in the atmosphere. In this chapter we discuss the thermochemical processes that determine the composition, structure, and characteristics of the Jovian clouds. We also discuss the significance of clouds in the big picture of the formation of giant planets and their atmospheres. We recommend multiprobes at all four giant planets in order to break new ground.

Correction to and updated reaction in “Chemical markers of possible hot spots on Mars”

Journal of Geophysical Research, 2005

Although there is no evidence of active volcanism on Mars today, ''localized'' outgassing sources... more Although there is no evidence of active volcanism on Mars today, ''localized'' outgassing sources, the hot spots, may not be ruled out. If outgassing does occur somewhere on Mars, water, carbon dioxide, sulfur species, methane, and to a lesser extent, halogens would be the likely molecules of outgassing, based on terrestrial analogs. The sulfur species, methane, and halogens have not been detected in the Martian atmosphere, but the observations were averaged over large areas, which could result in substantial dilution in abundances. If the interpretation of certain Mars Global Surveyor images indicating recent ground water seepage and surface runoff [Malin and Edgett, 2000] is correct, it may imply that Mars could still be active internally in some places from time to time, and outgassing of the abovementioned species may occur with or without the water seepage. Moreover, if the tentative detection of formaldehyde (CH 2 O) in the equatorial region of Mars [Korablev et al., 1993] is confirmed by future observations, it would imply at least local outgassing of methane, whose oxidation results in the formation of CH 2 O. Considering the possibility of outgassing from some localized hot spots, we have developed a one-dimensional photochemical model that includes methane (CH 4), sulfur dioxide (SO 2), and hydrogen sulfide (H 2 S), starting with their current ''global average'' upper limits of 0.02, 0.1, and 0.1 ppm at the surface, respectively, and then progressively increasing their abundances above possible hot spots. We find that the introduction of methane into the Martian atmosphere results in the formation of mainly formaldehyde, methyl alcohol (CH 3 OH), and ethane (C 2 H 6), whereas the introduction of the sulfur species produces mainly sulfur monoxide (SO) and sulfuric acid (H 2 SO 4). The effect of outgassed halogens on the Martian atmosphere is found to be negligible. Depending upon the flux of outgassed molecules from possible hot spots, some of these species and the resulting new molecules may be detectable locally, either by remote sensing or in situ measurements.

Chemical markers of possible hot spots on Mars

Journal of Geophysical Research, 2003

Correction to “Chemical markers of possible hot spots on Mars”

Journal of Geophysical Research, 2004

Models for Polar Haze Formation in Jupiter's Stratosphere

Icarus, 2002

We present coupled chemical-microphysical models for the formation, growth, and physical properti... more We present coupled chemical-microphysical models for the formation, growth, and physical properties of the jovian polar haze based on a gas-phase photochemical model for the auroral regions developed by A. S. Wong et al. (2000, Astrophys. J. 534, L215-217). In this model, auroral particle precipitation provides an important energy source for enhanced decomposition of methane and production of benzene and polycyclic aromatic hydrocarbons (PAHs). We find that at high altitude, A 4 (pyrene, a hydrocarbon consisting of four fused aromatic rings) should homogeneously nucleate to form tiny primary particles. At lower altitudes, A 3 (phenanthrene) and A 2 (naphthalene) heterogeneously nucleate on the A 4 nuclei. These particles subsequently grow by additional condensation of A 2 on the nucleated particles and by coagulation and eventually sediment out to the troposphere. We run different cases of the aerosol microphysical model for different assumptions regarding the fractal dimension of aggregate particles formed by the coagulation process. If coagulation is assumed to produce spherical particles (of dimensionality 3), then their mean radius at altitudes below the 20-mbar pressure level is computed to be approximately 0.1 µm. If coagulation produces fractal aggregates of dimension 2.1, then their equivalent mean radius below the 20-mbar level is much larger, of order 0.7 µm. Aggregates with fractal dimensions between 2.1 and 3 form with equivalent mean radii between 0.1 and 0.7 µm. In every case, mean particle radius is found to decrease with increasing altitude, as expected for a system approximately in sedimentationcoagulation equilibrium. The predicted range of altitudes where aerosol formation occurs and the mean size to which particles grow are found to be generally consistent with observations. However, our calculations cannot presently account for the large amount of total aerosol loading inferred by M. G. Tomasko et al. (1986, Icarus 65, 218-243). We suggest that the primarily neutral chemical pathway to heavy hydrocarbon and PAH formation proposed by Wong et al. (2000) may proceed too slowly to produce a sufficient amount of condensible material. Inclusion of ion and ion-neutral reactions in the chemical scheme could potentially lead to the prediction of

Evolution of CO on Titan

Icarus, 2002

The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopom... more The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopomers of CO, 13 CO and C 18 O, relative to 12 C 16 O. However, the original isotopic signatures may be altered by photochemical reactions. This paper explains why there is no isotopic enrichment in C in Titan's atmosphere, despite significant enrichment of heavy H, N, and O isotopes. We show that there is a rapid exchange of C atoms between the CH 4 and CO reservoirs, mediated by the reaction 1 CH 2 + * CO → 1 * CH 2 + CO, where * C is 13 C. Based on recent laboratory measurements, we estimate the rate coefficient for this reaction to be 3.2 × 10 −12 cm 3 s −1 at the temperature appropriate for the upper atmosphere of Titan. We investigate the isotopic dilution of CO using the Caltech/JPL one-dimensional photochemical model of Titan. Our model suggests that the time constant for isotopic exchange through the above reaction is about 800 Myr, which is significantly shorter than the age of Titan, and therefore any original isotopic enhancement of 13 C in CO may have been diluted by the exchange process. In addition, a plausible model for the evolution history of CO on Titan after the initial escape is proposed.

Electrical discharges and broadband radio emission by Martian dust devils and dust storms

Geophysical Research Letters, 2003

Triboelectric charging of saltating and colliding sand and dust particles produces strong electri... more Triboelectric charging of saltating and colliding sand and dust particles produces strong electric fields in terrestrial dust devils and dust storms. Acceleration of the charged particles, as well as microdischarges between them, generates wideband electromagnetic radiation. Similar phenomena are expected to be ubiquitous on Mars, because Martian dust devils and dust storms are larger, stronger and more frequent than their terrestrial analogues, and electrical discharges occur at a much lower potential gradient in the thin Martian atmosphere. We present theoretical arguments and observational evidence that Martian dust events produce nonthermal wideband electromagnetic radiation detectable from Earth.

Benzene and Haze Formation in the Polar Atmosphere of Jupiter

Geophysical Research Letters, 2003

Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the... more Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the polar atmosphere, giving rise to intense auroras [Clarke et al., 1996; Grodent et al., 2000]. An important consequence of this energy influx is the production of a dark haze [Pryor and Hord, 1991], the formation mechanism of which was hitherto poorly known. Recent observations of benzene on Jupiter [Bézard et al., 2001; Flasar, 2002] provide new clues for a chemical and aerosol model for the formation of heavy hydrocarbon aerosols. The chemistry begins with the destruction of methane by energetic particles, followed by neutral and ion reactions, ultimately leading to the formation of benzene and other complex hydrocarbons, including multi-ring compounds which subsequently condense. High temperatures and effective eddy mixing engendered by the auroras enhance the formation of heavy hydrocarbons and aerosols. This mechanism may be relevant in the atmospheres of Saturn and extrasolar giant planets, and is an example of how a planetary magnetosphere may influence the chemical composition and climate forcing of the upper atmosphere.