We present a new and improved version (V4.0) of the NASA standard nitrogen
dioxide (NO2) product from the Ozone Monitoring Instrument (OMI) on the
Aura satellite. This version incorporates the most salient improvements for
OMI NO2 products suggested by expert users and enhances the NO2
data quality in several ways through improvements to the air mass factors
(AMFs) used in the retrieval algorithm. The algorithm is based on
the geometry-dependent surface Lambertian equivalent reflectivity (GLER)
operational product that is available on an OMI pixel basis. GLER is
calculated using the vector linearized discrete ordinate radiative transfer
(VLIDORT) model, which uses as input high-resolution bidirectional
reflectance distribution function (BRDF) information from NASA's Aqua
Moderate Resolution Imaging Spectroradiometer (MODIS) instruments over land
and the wind-dependent Cox–Munk wave-facet slope distribution over water,
the latter with a contribution from the water-leaving radiance. The GLER
combined with consistently retrieved oxygen dimer (O2–O2)
absorption-based effective cloud fraction (ECF) and optical centroid
pressure (OCP) provide improved information to the new NO2 AMF
calculations. The new AMFs increase the retrieved tropospheric NO2 by
up to 50 % in highly polluted areas; these differences arise from both
cloud and surface BRDF effects as well as biases between the new MODIS-based
and previously used OMI-based climatological surface reflectance data sets.
We quantitatively evaluate the new NO2 product using independent
observations from ground-based and airborne instruments. The new V4.0 data
and relevant explanatory documentation are publicly available from the NASA
Goddard Earth Sciences Data and Information Services Center (https://disc.gsfc.nasa.gov/datasets/OMNO2_V003/summary/, last access: 8 November 2020),
and we encourage their use over previous versions of OMI NO2 products....

Ozone Monitoring Instrument (OMI) Aura nitrogen dioxide standard product version 4.0 with improved surface and cloud treatments

10.5194/amt-14-455-2021