Louis A. Capone

Galactic cosmic rays and N2 dissociation on Titan

The electromagnetic and particle cascade resulting from the absorption of galactic cosmic rays in the atmosphere of Titan is shown to be an important mechanism for driving the photochemistry at pressures of 1 to 50 mbar in the atmosphere. In particular, the cosmic ray cascade dissociates N2, a process necessary for the synthesis of nitrogen organics such as HCN. The important interactions of the cosmic ray cascade with the atmosphere are discussed. The N2 excitation and dissociation rates and the ionization rates of the principal atmospheric constituents are computed for a Titan model atmosphere that is consistent with Voyager 1 observations. It is suggested that HCN may be formed efficiently in the lower atmosphere through the photodissociation of methylamine. It is also argued that models of nitrogen and hydrocarbon photochemistry in the lower atmosphere of Titan should include the absorption of galactic cosmic rays as an important energy source.

Cosmic ray synthesis of organic molecules in Titan's atmosphere

The possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N2-CH4-H2 Titan model atmosphere has been studied. The cosmic-ray-induced ionization results in peak electron densities of 2000/cu cm, with NH(+), C3H9(+), and C4H9(+) being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of N(2D) reactions with CH4 and H2 is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater.

Cosmic ray ionization of the Jovian atmosphere

Abstract An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic ray-induced cascade may be especially importannt in ionizing the atmosphere at levels where the total number density exceeds 10 19 cm −3 (well below the ionospheric layers produced by solar euv). A model containing both positive and negative ion reactions has been employed to compute equilibrium electron and ion number densities. Peak electron number densities on the order of 10 3 cm −3 may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH 4 + and C n H m + cluster ions, with n ⩾ 2; it is suggested that the absorption of galactic cosmic ray energy at such relatively high pressures in the Jovian atmosphere (M ∾ 10 18 to 10 20 cm −3 ) and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.

SSTs, nitrogen fertilizer and stratospheric ozone

THE threat to stratospheric ozone from supersonic transport (SST) exhaust emissions has been a subject of controversy since Hampson1 first suggested that significant ozone reductions might be caused by discharged water vapour. Later, after Johnston2 and Crutzen3 pointed out that even larger ozone depletions might result from emitted nitrogen oxides, water vapour effects were considered to be relatively unimportant. In the intervening years, predictions of SST ozone modification have evolved with advancing scientific knowledge4–7. Using a recently revised model of the stratosphere8, we report here that a substantial ozone layer enhancement could accompany worldwide SST fleet operations, and that water vapour may be an important factor in SST assessments. We have also found that increased nitrogen fertiliser use might, likewise, enhance the ozone layer, in contrast with previous calculations of ozone reduction9–11.

Revised predictions of the effect on stratospheric ozone of increasing atmospheric N2O and chlorofluoromethanes - A two-dimensional model study

Abstract The perturbation of stratospheric ozone caused by a doubling of atmospheric N 2 O and by an increase of stratospheric chlorine of about 0.9 ppbv due to continued release of chlorofluoromethanes is simulated with the aid of a two-dimensional photochemical model and new measurements of OH reaction rate coefficients. The global mean O 3 decrease is revised upward from about 8.5% to about 14% for N 2 O doubling, but is reduced from about 1.6% to about 0.8% for 0.9 ppbv chlorine increase. The latitude variation of the O 3 perturbations as well as predictions of stratospheric OH abundance are also discussed.

Implications of smaller concentrations of stratospheric OH: A two-dimensional model study of ozone perturbations

Abstract There is growing observational evidence that stratospheric OH concentrations are smaller than models have been predicting. Using very recent HO x reaction rate coefficient measurements in a two-dimensional photochemical model, results which support these observations are obtained. As a consequence of smaller OH concentrations, we show that perturbations of stratospheric ozone by NO x (SST emissions and nitrogen fertilizers) may be larger than expected, while perturbations due to added water vapor and chlorine (SSTs and chlorofiuoromethanes. respectively) may be smaller.