Atmospheric Gases

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars.

The responses of alkylamine functionalized organic bridged polysilsesquioxanes on chemicapacitive sensors to carbon dioxide (CO 2 ) are described operating at temperatures ranging from 15 to 50°C. These hybrid organic-inorganic network materials were synthesized by the sol-gel polymerization of a mixture of a matrix monomer and functional monomer at various ratios followed by aging and ink-jet deposition of the sol on each capacitive sensor. During exposure of the sensor to known concentrations of analyte, the material's capacitance was measured. From these changes in capacitance, detection limits ranging from 40 to 100 ppm were calculated. Furthermore, a correlation was observed with increasing length of the alkyl chain in the amine monomer correlating with an increase in CO 2 sensitivity and a decrease in water sensitivity. These materials offer a new method for CO 2 detection for building control systems or other low-power applications using low operating temperatures.

Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chemical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteorological parameters were made on board the R/V Malcolm Baldridge prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of welldefined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in airmasses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over generation. The principal reaction leading to ozone destruction was O(•D) + H20-* 2OH. monoxide obtained during a cruise aboard the NOAA research ship Malcolm Baldrige during June 1992 are reported and interpreted in an effort to better understand the role of terrestrial gases in the marine boundary layer, specifically with respect to the effect of limited odd nitrogen concentration on ozone production and destruction. The cruise was organized as a

Density functional theory (DFT) was used to optimize the geometries and calculate the enthalpies for the interactions between polar (H 2 O), quadrupolar (CO 2 and N 2 ), and apolar (H 2 and CH 4 ) atmospheric gases with a cluster model of the Engelhard titanosilicate ETS-10 having sodium extra framework cations (Na-ETS-10). The DFT calculations were performed with different exchange-correlation functionals and were corrected for the basis set superposition error with the counterpoise method. The calculated enthalpies for the interaction of the five gases with Na-ETS-10 decrease in the order H 2 O > CO 2 ) N 2 % CH 4 > H 2 and compare well with experimental data available in the literature. The enthalpies calculated at the M06-L/6-31++G(d,p) level of theory for the two extreme cases, i.e., strongest and weakest interactions, are À60.6 kJ/mol (H 2 O) and À12.2 kJ/mol (H 2 ). Additionally, the calculated vibrational frequencies are in very good agreement, within the approximations of the method, with the characteristic vibrational modes of ETS-10 and of the interactions of gases with Na + in the 12-membered channel in ETS-10.

Geological and biological evidence suggests that Earth was warm during most of its early history, despite the fainter young Sun. Upper bounds on the atmospheric CO 2 concentration in the Late Archean/Paleoproterozoic (2.8-2.2 Ga) from paleosol data suggest that additional greenhouse gases must have been present. Methanogenic bacteria, which were arguably extant at that time, may have contributed to a high concentration of atmospheric CH 4 , and previous calculations had indicated that a CH 4 -CO 2 -H 2 O greenhouse could have produced warm Late Archean surface temperatures while still satisfying the paleosol constraints on pCO 2 . Here, we revisit this conclusion. Correction of an error in the CH 4 absorption coefficients, combined with the predicted early onset of climatically cooling organic haze, suggest that the amount of greenhouse warming by CH 4 was more limited and that pCO 2 must therefore have been Ն0.03 bar, at or above the upper bound of the value obtained from paleosols. Enough warming from CH 4 remained in the Archean, however, to explain why Earth's climate cooled and became glacial when atmospheric O 2 levels rose in the Paleoproterozoic. Our new model also shows that greenhouse warming by higher hydrocarbon gases, especially ethane (C 2 H 6 ), may have helped to keep the Late Archean Earth warm.

An equivalent circuit model is proposed for the Schottky barrier at the junction between a metallic electrode and a semiconducting carbon nanotube (NT). We have applied the model to a gold-NT junction under the presence of neutral polarized NH3 molecules, and have shown that visible Schottky barrier modulation is possible for the gas densities as low as 3 x 10^13 cm−2, which is quite feasible experimentally.