Atmospheric chemistry-climate feedbacks

We extend the theory of climate feedbacks to include atmospheric chemistry. A change in temperature caused by a radiative forcing will include, in general, a contribution from the chemical change that is fed back into the climate system; likewise, the change in atmospheric burdens caused by a chemical forcing will include a contribution from the associated climate change that is fed back into the chemical system. The theory includes two feedback gains, G_(che) and G_(cli). G_(che) is defined as the ratio of the change in equilibrium global mean temperature owing to long-lived greenhouse gas radiative forcing, under full climate-chemistry coupling, to that in the absence of coupling. G_(cli) is defined as the ratio of the change in equilibrium mean aerosol or gas-phase burdens owing to chemical forcing under full coupling, to that in the absence of coupling. We employ a climate-atmospheric chemistry model based on the Goddard Institute for Space Studies (GISS) GCM II', including tropospheric gas-phase chemistry, sulfate, nitrate, ammonium, black carbon, and organic carbon. While the model describes many essential couplings between climate and atmospheric chemistry, not all couplings are accounted for, such as indirect aerosol forcing and the role of natural dust and sea salt aerosols. Guided by the feedback theory, we perform perturbation experiments to quantify G_(che) and G_(cli). We find that G_(che) for surface air temperature is essentially equal to 1.00 on a planetary scale. Regionally, G_(che) is estimated to be 0.80–1.30. The gains are small compared to those of the physical feedbacks in the climate system (e.g., water vapor, and cloud feedbacks). These values for G_(che) are robust for the specific model used, but may change when using more comprehensive climate-atmospheric chemistry models. Our perturbation experiments do not allow one to obtain robust values for G_(cli). Globally averaged, the values range from 0.99 to 1.28, depending on the chemical species, while, in areas of high pollution, G_(cli) can be up to 1.15 for ozone, and as large as 1.40 for total aerosol. These preliminary values indicate a significant role of climate feedbacks in the atmospheric chemistry system

Lookup tables to compute high energy cosmic ray induced atmospheric ionization and changes in atmospheric chemistry

A variety of events such as gamma-ray bursts and supernovae may expose the Earth to an increased flux of high-energy cosmic rays, with potentially important effects on the biosphere. Existing atmospheric chemistry software does not have the capability of incorporating the effects of substantial cosmic ray flux above 10 GeV . An atmospheric code, the NASA-Goddard Space Flight Center two-dimensional (latitude, altitude) time-dependent atmospheric model (NGSFC), is used to study atmospheric chemistry changes. Using CORSIKA, we have created tables that can be used to compute high energy cosmic ray (10 GeV - 1 PeV) induced atmospheric ionization and also, with the use of the NGSFC code, can be used to simulate the resulting atmospheric chemistry changes. We discuss the tables, their uses, weaknesses, and strengths.Comment: In press: Journal of Cosmology and Astroparticle Physics. 6 figures, 3 tables, two associated data files. Major revisions, including results of a greatly expanded computation, clarification and updated references. In the future we will expand the table to at least EeV levels

Atmospheric Chemistry of Venus-like Exoplanets

We use thermodynamic calculations to model atmospheric chemistry on terrestrial exoplanets that are hot enough for chemical equilibira between the atmosphere and lithosphere, as on Venus. The results of our calculations place constraints on abundances of spectroscopically observable gases, the surface temperature and pressure, and the mineralogy of the surface. These results will be useful in planning future observations of the atmospheres of terrestrial-sized exoplanets by current and proposed space observatories such as the Hubble Space Telescope (HST), Spitzer, James Webb Space Telescope (JWST), Terrestrial Planet Finder, and Darwin.Comment: 35 pages, 4 figures, 3 tables; 1 appendix; submitted to ApJ; version

The Peculiar Atmospheric Chemistry of KELT-9b

The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetics calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which is expected to be cloudfree, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. Due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. Carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. All of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron and magnesium are predicted to have relative abundances as high as 1 part in 10,000. Neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes KELT-9b suitable for high-resolution ground-based spectroscopy with HARPS-N or CARMENES. We summarize future observational prospects of characterizing the atmosphere of KELT-9b.Comment: Accepted by ApJ. 9 pages, 6 figures. Corrected minor errors in Figures 1a and 1b (some line styles were switched by accident), text and conclusions unchanged, these minor changes will be updated in final ApJ proo

Computational solution of atmospheric chemistry problems

Extensive studies were performed on problems of interest in atmospheric chemistry. In addition to several minor projects, four major projects were performed and described (theoretical studies of ground and low-lying excited states of ClO2; ground and excited state potential energy surfaces of the methyl peroxy radical; electronic states ot the FO radical; and theoretical studies S02 (H2O) (sub n))

Research in atmospheric chemistry and transport

The carbon monoxide cycle was studied by incorporating the known CO sources and sinks in a tracer model which used the winds generated by a general circulation model. The photochemical production and loss terms, which depended on OH radical concentrations, were calculated in an interactive fashion. Comparison of the computed global distribution and seasonal variations of CO with observations was used to yield constraints on the distribution and magnitude of the sources and sinks of CO, and the abundance of OH radicals in the troposphere

Atmospheric Chemistry Modelling of Amine Emissions from Post Combustion CO2 Capture Technology

Emissions from post combustion CO2 capture plants using amine solvents are of concern due to their adverse impacts on the human health and environment. Potent carcinogens such as nitrosamines and nitramines resulting from the degradation of the amine emissions in the atmosphere have not been fully investigated. It is, therefore, imperative to determine the atmospheric fate of these amine emissions, such as their chemical transformation, deposition and transport pathways away from the emitting facility so as to perform essential risk assessments. More importantly, there is a lack of integration of amine atmospheric chemistry with dispersion studies. In this work, the atmospheric chemistry of the reference solvent for CO2 capture, monoethanolamine, and the most common degradation amines, methylamine and dimethylamine, formed as part of the post combustion capture process are considered along with dispersion calculations. Rate constants describing the atmospheric chemistry reactions of the amines of interest are obtained using theoretical quantum chemistry methods and kinetic modeling. The dispersion of these amines in the atmosphere is modeled using an air-dispersion model, ADMS 5. A worst case study on the UK's largest CO2 capture pilot plant, Ferrybridge, is carried out to estimate the maximum tolerable emissions of these amines into the atmosphere so that the calculated concentrations do not exceed guideline values and that the risk is acceptable

Earth Observing System. Volume 1, Part 2: Science and Mission Requirements. Working Group Report Appendix

Areas of global hydrologic cycles, global biogeochemical cycles geophysical processes are addressed including biological oceanography, inland aquatic resources, land biology, tropospheric chemistry, oceanic transport, polar glaciology, sea ice and atmospheric chemistry

Titan

The following topics are discussed with respect to Titan: observations of the atmosphere; laboratory simulations and theoretical models of Titan's atmosphere; endpoints of atmospheric chemistry - aerosols and oceans; exobiology; and the next steps in understanding Titan