https://backend.orbit.dtu.dk/ws/files/145750384/Nreview_revised.pdf

Modeling nitrogen chemistry in combustion

Experimental and modeling study on the high-temperature oxidation of Ammonia and related NOx chemistry

The oxidation of hydrogen cyanide and related chemistry

Our purpose is to release a chemical network, and the associated rate coefficients, developed for the temperature and pressure range relevant to hot Jupiters atmospheres. Using this network, we study the vertical atmospheric composition of the two hot Jupiters (HD209458b, HD189733b) with a model that includes photolyses and vertical mixing and we produce synthetic spectra. The chemical scheme is derived from applied combustion models that have been methodically validated over a range of temperatures and pressures typical of the atmospheric layers influencing the observations of hot Jupiters. We compare the predictions obtained from this scheme with equilibrium calculations, with different schemes available in the literature that contain N-bearing species and with previously published photochemical models. Compared to other chemical schemes that were not subjected to the same systematic validation, we find significant differences whenever non-equilibrium processes take place. The deviations from the equilibrium, and thus the sensitivity to the network, are more important for HD189733b, as we assume a cooler atmosphere than for HD209458b. We found that the abundances of NH3 and HCN can vary by two orders of magnitude depending on the network, demonstrating the importance of comprehensive experimental validation. A spectral feature of NH3 at 10.5$\mu$m is sensitive to these abundance variations and thus to the chemical scheme. Due to the influence of the kinetics, we recommend the use of a validated scheme to model the chemistry of exoplanet atmospheres. Our network is robust for temperatures within 300-2500K and pressures from 10mbar up to a few hundreds of bars, for species made of C,H,O,N. It is validated for species up to 2 carbon atoms and for the main nitrogen species.

/pdf/a-chemical-model-for-the-atmosphere-of-hot-jupiters-3btml1l3q8.pdf

A chemical model for the atmosphere of hot Jupiters

The nitrogen stable isotope ratio of NOx (δ(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of δ(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of δ(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and δ(15)N-NOx was analyzed. The vehicles sampled in this study emitted δ(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted δ(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 1.5‰, with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current δ(15)N-NOx values emitted from vehicles.

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Nitrogen stable isotope composition (δ15N) of vehicle-emitted NOx.

Atomic resonance absorption spectroscopy is presently used to measure the dissociation of N/sub 2/ behind reflected shock waves in the 3390-6435 K temperature range, allowing direct observation of N atom formation in the postshock reaction zone. Attention is given to experiments performed in N/sub 2/-Ar mixtures at 0.9-2.1-bar pressures; reaction rate coefficients are directly determinable on the basis of N atom concentrations. 10 references.

Knut Thielen

Papers

N Atom Measurements in High-Temperature N2 Dissociation Kinetics

Resonance absorption measurements of N, O, and H atoms in shock heated HCN/O2/Ar mixtures