The Principal Investigator (PI) plans to develop a theoretical framework to calculate pressure-broadened half-widths and pressure-induced line shifts for trace gases in the terrestrial atmosphere. The half-width remains the major source of error in the spectral parameters used for reducing remote sensing data and in line-by-line models used to calculate radiative forcing from greenhouse gases. The inclusion of the line shift in profile retrievals also reduces the error in the procedure. For applications to the Earth's atmosphere, data are needed for thousands of ro-vibrational transitions. Hence a theoretical model is needed that is computationally efficient and capable of determining gamma and delta within the needs of the spectroscopic and remote sensing communities. In this work the temperature dependence of the half-width and the line shift will be investigated. The vibrational state, rotational state, and temperature dependence of these collision-induced parameters will be investigated.
Broader impacts include education of a postdoctoral student and three undergraduate students in the research project. The work will also provide resources for research and education. All the results of the calculations will be made available online (http://faculty.uml.edu/Robert_Gamache). The line shape information for atmospheric molecules will be incorporated into the HITRAN molecular absorption parameter database for use by the community. The contributions beyond science and engineering are that the results will be used by the remote sensing community and will allow them more confidence in their data. These results will allow a better understanding about planet Earth, its energy balance, how the concentration of ozone and other gases are changing with time, and how climate is evolving. This knowledge will allow for better regulation and stewardship of the planet's interacting systems and will allow better presentations of the information to the citizens of the United States and the world.
Line shape parameters and their temperature dependence for molecules of importance in Earth’s atmosphere In order to better understand the effects of human activities on the health of our planet and its peoples, the international community has made a commitment to actively monitor the state of Earth-atmosphere system. The main problems motivating these actions are well known: ozone depletion, global climate change, and atmospheric pollution. For example, emissions from coal-fired power-plants in China are now causing pollution in western United States and Canada. Science can provide knowledge about the structure, chemistry, composition, and dynamics of the earth-atmosphere system globally so that policy makers can make informed, intelligent decisions to guarantee the health and prosperity of our planet. The scale of the problem, i.e. to monitor the whole Earth, makes remote sensing measurements, which include ground based, balloon-borne, aircraft, rocket, and satellite observations, using a technique called spectroscopy a key part of the overall strategy. These spectroscopic instruments measure the spectra of molecules in the atmosphere. The spectra appear as a series of "lines," which can be thought of as a unique fingerprint for every molecule. These fingerprints allow scientists to determine which gases and at what concentrations at different altitudes (called profiles) are in the atmosphere. Continuous observation, usually from satellites, allows the tracking of the movement of molecules around the globe and their chemical interactions. From these data scientists can determine the effects of these anthropogenic and natural gases on the environment. However, to understand the observations the basic parameters (line position, intensity, and shape of the line) of the spectra must be known accurately. Currently the largest source of uncertainty in the spectroscopic parameters that are used for determining molecular profiles is the shape of the line. Because there are many thousands of lines for which the spectroscopic information is needed at multiple pressures and temperatures representative of the atmosphere, measuring all the lines is impractical. However, measurements serve as the benchmark for theory and a successful theory can contribute to the spectroscopic picture in uniquely useful ways. In this work the Complex Robert-Bonamy (CRB) theory was used to calculate the line shape parameters for a number of molecules in the terrestrial and in planetary atmospheres to provide the needed information to the leading spectroscopic parameter database (HITRAN) used to interpret the remotely sensed data. The CRB formulation is the best available method for determining the line shape and shows excellent agreement with measurement. For example, recent calculations on CO2 showed a 1-2% standard deviation when compared to measurement. From this work line shape information for thousands of lines was determined for water vapor (H2O), carbon dioxide (CO2), nitric acid (HNO3), formaldehyde (H2CO), methyl cyanide (CH3CN) in the Earth’s atmosphere. In addition line shape calculations were made for H2O, monodeuterated water vapor (HDO), and CO2 in the atmospheres of Mars and Venus. Work was also undertaken in collaboration with the HITRAN database to improve other spectral parameters, to add the line shape parameters to the database for atmospheric and high temperature applications, and to allow the spectral intensity parameter to be extended to higher temperatures and to molecules of astrophysical interest. These data are available on the web site of the principal investigator (faculty.uml.edu/Robert_Gamache) and in the supplementary information area of the journals in which the work was published. The main contribution to other disciplines is providing greatly improved line shape parameters and their temperature dependence to scientists modeling the Earth-atmosphere system. This work will improve our confidence in spectroscopic remote sensing measurements and allow a better determination of the state of the atmosphere. The results will allow a better understanding of planet Earth, its energy balance, how the concentration of ozone and other gases are changing with time, and how climate is evolving. This knowledge will allow for better regulation and stewardship of the planet's interacting systems and will allow the information to be presented with enhanced confidence to the citizens of the USA and the world.
