Nitrogen Data Fields

NO₂ Concentration

The NO₂ concentration field and associated error are given in units of mol/m³. Multiply by \(6.02214076 \times 10^{17}\) to convert these fields to units of molecules/cm³.

NO2_concentration: Mole concentration of NO₂ in units of mol/m³. Only converged values in the retrieval range and above any cloud layer are reported.

The associated error in the retrieved NO₂ is given by:

NO2_concentration_standard_error: Standard uncertainty of the retrieved NO₂ concentration in units of mol/m³.

The vertical resolution is computed for every retrieved profile from the FWHM of the averaging kernel and is given by:

vertical_resolution: FWHM of the averaging kernel, with units of km.

Although not recommended for general use, the field _rtm_internal_NO2_concentration may be useful in investigating possible biases due to retrieval saturation or other similar effects. This field includes altitudes affected by clouds and those that have not fully converged.

_rtm_internal_NO2_concentration: The full ozone concentration profile as used in the SASKTRAN radiative transfer model in units of mol/m³.

Derived Nitrogen Products

Including in the nitrogen files are additional NO, NO₂, and NO_x profiles derived from the retrieved NO₂ and shifted to different times of the day using the PRATMO photochemical box model. These are:

derived_0630_NO2_concentration: Mole concentration of NO₂ shifted to a local solar time of 06:30 in units of mol/m³.
derived_daily_mean_NO2_concentration: Daily mean of mole concentration of NO₂ in units of mol/m³.
derived_1200_NO2_concentration: Mole concentration of NO₂ shifted to local solar noon in units of mol/m³.
derived_local_solar_time_NO_concentration: Mole concentration of NO at the local solar time of the measurement in units of mol/m³.
derived_0630_NO_concentration: Mole concentration of NO shifted to a local solar time of 06:30 in units of mol/m³.
derived_daily_mean_NO_concentration: Daily mean of NO in units of mol/m³.
derived_1200_NO_concentration: Mole concentration of NO shifted to local solar noon in units of mol/m³.
derived_local_solar_time_NOx_concentration: Mole concentration of NO_x at the local solar time of the measurement in units of mol/m³.
derived_0630_NOx_concentration: Mole concentration of NO_x shifted to a local solar time of 06:30 in units of mol/m³.
derived_daily_mean_NOx_concentration: Daily mean of NO_x in units of mol/m³.
derived_1200_NOx_concentration: Mole concentration of NO_x shifted to local solar noon in units of mol/m³.

Clouds

The cloud altitudes retrieved during the aerosol extinction retrieval. Clouds are separated into two categories:

cloud_top_altitude: The altitude, in km, of the top of a cloud detected in this profile, NaN otherwise
psc_altitude: The altitude, in km, of a polar stratospheric cloud detected in this profile, NaN otherwise

Note

While the ozone concentration is reported in _rtm_internal_NO2_concentration when clouds are flagged, it is unlikely to be a reliable quantitative measure, as assumptions made in the retrieval are not consistent with cloud microphysics.

Meteorology

A few meteorological fields are included in the data to aid in analysis.

temperature: Temperature taken from MERRA 2 and interpolated to the current geometrical altitude grid.
pressure: Pressure in hPa taken from MERRA 2 and interpolated to the current geometrical altitude grid.
tropopause_altitude: Tropopause in km based on WMO lapse-rate tropopause definition; the first parameter for the lowest tropopause.Calculated from MERRA 2 temperature profiles.

Geometry

For ease of use, each OSIRIS scan is assigned to a specific geographic location and time. This is not strictly true, as a scan takes approximately 90 seconds to complete and spans a few degrees latitude over this time. The geometric data fields are defined at the 30 km point of each scan.

latitude: latitude in degrees north
longitude: longitude in degrees east
time: days since 1900-01-01 00:00:00
local_solar_time: Local solar time in hours

In addition to the geographic location, three solar angles are provided that define the measurement geometry of the line of sight with respect to sun.

ssa: Solar scattering angle. The angle between the line of sight and the solar beam.
sza: Solar zenith angle. The angle between solar beam and the vertical direction at the tangent point.
saa: Solar azimuth angle. The angle between the horizontal projection of the solar beam and the line of sight.

Additional Fields

albedo: The retrieved albedo of the surface.

Retrieval

These fields provide information about the retrieved NO₂ concentration profiles. It should be noted that values below retrieval_lowerbound are truncated from NO2_concentration. Profiles with poor convergence are also filtered from this product.

retrieval_lowerbound: Lowest altitude in km that is valid for the NO₂ retrieval.
convergence_ratio: Convergence ratio of the NO₂ retrieval.
chi_sq: The \({\chi}\)² value of the NO₂ retrieval.