Photochemical modelling of Venus clouds using Pioneer Venus data

In order to understand the evolution of water on Venus, we must know the hydrogen escape flux as a function of the tropospheric water abundance. We have studied the connection between total stratospheric hydrogen and exobase hydrogen available to non-thermal escape processes and examined the details of the photochemical trap for water at the Venus cloud tops. Our immediate goal is to calculate the stratospheric water abundance as a function of the tropospheric water abundance. Photochemical production of H2SO4 acts as a sink for both water and sulfur and is capable of keeping stratospheric abundances low if a proper balance exists between the tropospheric abundances. If production of H2SO4 were the only sink for H2O and SO2, the excess in tropospheric abundance of one over the other would reach the stratosphere, and the functional dependence of stratospheric H2O on tropospheric H2O would be linear near the present state. On Venus, however, sulfuric acid condenses at cloud top temperatures and the resulting aerosols can absorb additional water of hydration. This complicates the water budget, increasing the efficiency of sulfur as a sink for water. We have investigated the balance between tropospheric H2O and SO2 and how delicate the balance is. Our major conclusions from this work are the following: (1) H2O and SO2 are mutually limiting if proper tropospheric balance is maintained; (2) changes in tropospheric abundances on the order of 5 ppm are significant; and (3) changes in mixing rates near the cloud tops can cause dramatic changes in SO2 without causing dramatic changes in H2O

The atmosphere and ionosphere of Io

A variety of models for Io's atmosphere, ionosphere, surface, and environment are developed and discussed in the context of recent observational data. The sodium emission detected by Brown appears to require a collisional excitation process in Io's atmosphere, and the extended sodium emission measured by Trafton et al. may require scattering of the planetary radiation by an extended sodium cloud. The sodium is presumably present initially in bound form on Io's surface and may be released by the sputtering mechanism suggested by Matson et al. The ionosphere detected by the radio occultation experiment on Pioneer 10 could be attributed to photoionization of atmospheric sodium if Io's atmosphere could sustain significant vertical motions, of order 1 s^(-1) directed up during the day, down at night. Vertical motions of this magnitude could be driven by condensation of atmospheric NH_3. The total density of gas at Io's surface appears to lie in the range 10^(10)-10^(12) molecules cm^(-3). Corpuscular ionization could play an additional role for the Ionosphere. In this case the satellite should exhibit an exceedingly bright, ~ 10 kR, airglow at Lɑ. The incomplete hydrogen torus observed by Judge and Carlson in the vicinity of Io requires a large supply of hydrogen from the satellite's atmosphere. The escape flux should be of order 10^(11) cm^(-2) s^(-1) and could be maintained by photolysis of atmospheric NH_3. The observed geometry of the hydrogen torus appears to require a surprisingly short lifetime, ~ 10^5 s, for neutral hydrogen near Io's orbit, and may indicate the presence of a large flux, ~ 10^9 cm ^(-2) s^(-1), of low-energy protons in Jupiter's magnetosphere. Implications of the hydrogen torus for the energy and mass balance of Jupiter's magnetosphere are discussed briefly, and observational programs are identified which might illuminate present uncertainties in our understanding of Io

Photochemistry of the Venus Atmosphere

Carbon monoxide, produced in the Venus atmosphere by photolysis of CO_2, is removed mainly by reaction with OH. The radical OH is formed in part by photolysis of H_2O_2, in part by reaction of O with HO_2. Photolysis of HCl provides a major source of H radicals near the visible clouds of Venus and plays a major role in the overall photochemistry. The mixing ratio of O_2 is estimated to be approximately 10^(−7), about a factor of 10 less than a recent observational upper limit reported by Traub and Carleton. A detailed model, which accounts for the photochemical stability of Venus CO_2, is presented and discussed

The chemistry of atmospheric bromine

Bromine may act as a catalyst for recombination of ozone and could be more efficient than either nitric oxide or chlorine. The lower atmosphere contains small concentrations of gaseous bromine produced in part by marine activity, in part by volatilization of particulate material released during the combustion of leaded gasoline, with an additional contribution due to the use of methyl bromide as an agricultural fumigant. Observations by Lazrus et. al. (1975) indicate small concentrations of bromine, ∼ 10^(−11) (v/v) in the contemporary stratosphere and appear to imply a reduction of approximately 0.3% in the global budget of O_3. Estimates are given for future reductions in O_3 which might occur if the use of CH_3Br as an agricultural fumigant were to continue to grow at present rates

Photochemistry and evolution of Mars' atmosphere: A Viking perspective

Viking measurements of the Martian upper atmosphere indicate thermospheric temperatures below 200°K, temperatures much colder than those implied by remote sensing experiments on Mariner 6, 7, and 9 and Mars 3. The variability in thermospheric temperature may reflect an important dynamical coupling of upper and lower regions of the Martian atmosphere. Absorption of extreme ultraviolet solar radiation can account for observed features of the ionosphere and provides an important source of fast N and O atoms which may escape the planet's gravitational field. Isotopic measurements of oxygen and nitrogen impose useful constraints on models for planetary evolution. It appears that the abundance of N_2 in Mars' past atmosphere may have exceeded the abundance of CO_2 in the present atmosphere and that the planet also has copious sources of H_2O. The planet acquired its nitrogen atmosphere early in its history. The degassing rate for nitrogen in the present epoch must be less than the time-averaged degassing rate by at least a factor of 20

Sodium Emission from Io: Implications

The surface of lo may be covered with a layer of ammonia ice containing trace amounts of sodium potassium, and calcium; and atmospheric nitrogen could be formed as a photochemical product of ammonia photolysis. Intense sporadic sodium emission from Io can be excited by collisions involving vibrationally excited nitrogen molecules. These metastable molecules may be formed by electron impact, with electrons energized by an auroral mechanism. In order to account for the intensity ratio of the sodium doublet, it is necessary to invoke scattering in a thick gaseous envelope ejected by Io

Sources and sinks for atmospheric N_2O

Observations of the temporal and spatial distribution of N_2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N_2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N_2O. The gas is removed in the atmosphere by photolysis and by reaction with O(¹D), and there may be additional sinks in the ocean

Sources and sinks for atmospheric N2O

Observations of the temporal and spatial distribution of N2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N2O. The gas is removed in the atmosphere by photolysis and by reaction with O(1D), and there may be additional sinks in the ocean

Ozone depletion, greenhouse gases, and climate change

This symposium was organized to study the unusual convergence of a number of observations, both short and long term that defy an integrated explanation. Of particular importance are surface temperature observations and observations of upper atmospheric temperatures, which have declined significantly in parts of the stratosphere. There has also been a dramatic decline in ozone concentration over Antarctica that was not predicted. Significant changes in precipitation that seem to be latitude dependent have occurred. There has been a threefold increase in methane in the last 100 years; this is a problem because a source does not appear to exist for methane of the right isotopic composition to explain the increase. These and other meteorological global climate changes are examined in detail

Prospects for shale gas production in China: Implications for water demand

AbstractDevelopment of shale gas resources is expected to play an important role in China's projected transition to a low-carbon energy future. The question arises whether the availability of water could limit this development. The paper considers a range of scenarios to define the demand for water needed to accommodate China's projected shale gas production through 2020. Based on data from the gas field at Fuling, the first large-scale shale gas field in China, it is concluded that the water intensity for shale gas development in China (water demand per unit lateral length) is likely to exceed that in the US by about 50%. Fuling field would require a total of 39.9–132.9Mm3 of water to achieve full development of its shale gas, with well spacing assumed to vary between 300 and 1000m. To achieve the 2020 production goal set by Sinopec, the key Chinese developer, water consumption is projected to peak at 7.22Mm3 in 2018. Maximum water consumption would account for 1% and 3%, respectively, of the available water resource and annual water use in the Fuling district. To achieve China's nationwide shale gas production goal set for 2020, water consumption is projected to peak at 15.03Mm3 in 2019 in a high-use scenario. It is concluded that supplies of water are adequate to meet demand in Fuling and most projected shale plays in China, with the exception of localized regions in the Tarim and Jungger Basins