1. Is there any cost to obtain HITRAN?

No. The HITRAN database and its associated compilations are free.

2. Are the line positions in HITRAN in vacuum or air?

The transitions (line positions) in the HITRAN database are given as vacuum wavenumbers (cm-1). The intervals for the IR and UV cross-sections are likewise given in vacuum wavenumbers.

3. What are the units of intensity in HITRAN?

The units for intensity in HITRAN are cm-1/( molecule · cm-2 ) at the standard HITRAN temperature of 296 K. This unit has been chosen for its convenience for input to transmission and radiance modeling computer codes. An illustration of the definition of intensity, line position, and half-width is given in Fig. 1 of the Appendix to the article on the 1996 Edition of HITRAN: Rothman et al., Journal of Quantitative Spectroscopy and Radiative Transfer 60, 665-710 (1998). [link to article]

4. Does HITRAN model the atmosphere?

HITRAN is a database, not a “simulation” code. It provides a suite of parameters that are used as input to various modeling codes, either very high-resolution line-by-line codes, or moderate spectral resolution band-model codes. These radiative-transfer codes are based on the Beer-Lambert law of attenuation and may include many more features of modeling, for example scattering, continuum absorption, atmospheric constituent profiles, etc.

5. Are the data in HITRAN observed or calculated?

The parameters in HITRAN are a mixture of direct observations, theoretical calculations, and semi-empirical values. The calculations are the result of various quantum-mechanical solutions. The goal of HITRAN is to have a theoretically self-consistent set of parameters, while at the same time attempting to maximize the accuracy. References for the source are included for the most important parameters on each line of the database.

6. How does one convert intensity units between different databases?

This document describes the units adopted within the HITRAN database. There is also an example of converting the intensities from either the Jet Propulsion Laboratory or Cologne Database for Molecular Spectroscopy databases to HITRAN units.

7. What happens when a transition does not have a certain parameter, for instance a value for broadening by helium?

In this case for any user-defined custom output format (excluding the traditional .par output), the field space (length) dedicated to this parameter will be filled with "#" signs. Note that in the traditional .par output file there are only two cases where parameters may not have a value: (1) for unassigned lines there are sometimes missing lower-state energies which are substituted with the flag "-1" (2) for missing sets of quantum numbers, which are replaced by blank spaces.
  Users should take all of these situations into account when creating programs designed to work with the database.

8. What is “HITRAN-PC”?

HITRAN-PC is a commercial software product for laser remote sensing of the atmosphere that uses the HITRAN, EPA, or PNNL databases to calculate high-resolution molecular absorption and aerosol attenuation for horizontal or slant paths, different atmospheric models, and gas plume geometries. It was developed for easy use on a PC by Professor Dennis Killinger and Drs. William Wilcox and Denis Pliutau at the University of South Florida (Killinge@usf.edu; ref. D. K. Killinger, "HITRAN-PC: 25 Years of Academic Development…," J. of Technology and Innovation 14, 303-327 (2012) and is distributed by the Ontar Corporation (http://www.ontar.com).

9. What happens, when in the line-by-line data selection, one chooses the option "Select All" molecules and then selects all isotopologues and does not specify the spectral range? In other words, when one requests the entire line-by-line dataset.

While we strongly encourage users to select only the data that they actually need, the server will still create files for the entire dataset if requested. It will just take a long time to build. The user can retrieve these files from their individual "Search History" which can be accessed by clicking on the "Clock" icon in the upper right corner.

10. How do I obtain the values of the partition sums?

Values of the partition sums for almost all of the isotopologues in the line-by-line portion of HITRAN can be obtained by downloading the text files in the 8th column in the table for Isotopologue Metadata under Documentation in HITRANonline (https://hitran.org/docs/iso-meta/). These files, Q(T), give the partition sums in intervals of one degree K from 1 degree to a maximum temperature of 3000K or above, depending on the reliability of the method available for their calculation.

11. When should I use HITEMP instead of HITRAN?

If your application requires temperatures well in excess of terrestrial atmospheric temperatures, it is preferable to use HITEMP rather than HITRAN. HITRAN has an intensity cut off for line transitions, whereas HITEMP endeavors to include many additional bands (hot bands, difference bands, etc) that become significant at elevated temperatures. We are actively working on expanding the number of molecules available via HITEMP, but at this time only H2O, CO2, N2O, CO, CH4, NO, NO2, and OH are incorporated into HITEMP. Access to HITEMP can be made under the Data Access menu in HITRANonline (https://hitran.org/hitemp/).