Aura OMI¶

Ozone Monitoring Instrument (OMI) on Aura — Level 2 and Level 3 Collection 4 (V004) trace gas and aerosol products (total ozone, NO2, SO2, HCHO and more)

Available

At a glance¶

Note on period: Science observations began on 1 October 2004 (Aura launched 2004-07-15). As checked on 2026-10-13, V004 OMNO2d, OMTO3d and OMSO2e run to 10–11 October 2026. The latest OMHCHO V004 file in CMR is for 30 April 2025, so recent HCHO data are not yet available. OMNO2d V003 stopped at 2026-03-15.

Overview¶

OMI is a UV–visible imaging spectrometer built by the Netherlands and Finland and flown on NASA's Aura satellite. Since 2004 it has measured total ozone, nitrogen dioxide (NO2), sulphur dioxide (SO2), formaldehyde (HCHO), the UV aerosol index and more, with near-global coverage every day. GES DISC distributes the along-orbit L2 swath data and L3 daily products gridded at 0.25° and 1°. With more than 20 years of data it is a reference for air quality trends, emission estimates and ozone layer monitoring; Collection 4 (V004), reprocessed in 2024–2025, is the current version.

What changes with the successor¶

OMI Collection 3 (V003) → OMI Collection 4 (V004)¶

Transition: 2024-12

A reprocessing of the full record (from October 2004) using recalibrated Collection 4 L1B radiances. Release dates differ by product: NO2 came first in December 2024, followed by ozone, SO2 and HCHO during 2025. Values change between versions, so do not mix V004 with V003.

Sources: OMNO2 Collection 4 v5.0 README (2024-12) · OMSO2 V004 README (v2.1.0, 2025-06-17) · OMHCHO V004 README (2026-02-28) · CMR — OMTO3d V004 collection record

Aura OMI → Sentinel-5P TROPOMI Planned¶

Transition: 2028-08

Since April 2018 TROPOMI has observed from the same early-afternoon orbit (13:30 equator crossing) with pixels more than ten times smaller, making it OMI's de facto successor. The two records overlap from 2018, so the usual approach is to calibrate their differences over that period before joining them; Aura science operations are projected to end around August 2028.

Sources: Levelt et al. (2018) The Ozone Monitoring Instrument — overview of 14 years in space, ACP · Veefkind et al. (2012) TROPOMI on the ESA Sentinel-5 Precursor, RSE · NASA — Potential Evolution of the Aura Mission (updated 2026-09-08) · CMR — OMI_MINDS_NO2 V2 (MEaSUREs multi-satellite NO2)

Compare the two side by side

Available variables¶

Names as given in the GES DISC READMEs and file specifications (.fs). Most L2 and L3 files are HDF-EOS5 (.he5), with variables under HDFEOS/SWATHS/…/Data Fields or HDFEOS/GRIDS/…/Data Fields; OMHCHO V004 is netCDF4. The OMNO2d fill value is −1.26765×10^30.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

L3 NO2 (OMNO2d, 0.25° daily)¶

L3 ozone and aerosol index (OMTO3d, 1° daily)¶

L2 NO2, SO2 and HCHO swaths (OMNO2, OMSO2, OMHCHO)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA GES DISC — OMI datasets — Web, HTTPS, OPeNDAP, subsetting
  • Product pages include OMNO2d_004, OMTO3d_004, OMSO2e_004, OMNO2_004, OMSO2_004 and OMHCHO_004. A free Earthdata Login is required.
• Earthdata Cloud HTTPS directory (data.gesdisc.earthdata.nasa.gov) — HTTPS (wget/curl, Earthdata Login)
  • File paths follow …/Aura_OMI_Level3/OMNO2d.004/YYYY/. The legacy servers (acdisc and aura.gesdisc.eosdis.nasa.gov) may close at any time after 30 September 2026.
• NASA Earthdata Search — OMNO2d V004 — Earthdata Search / earthaccess
• NASA Giovanni — Web maps and time series
  • Handy for checking magnitudes and gap patterns with area-mean time series or maps before downloading.

Example code¶

Downloads OMNO2d V004 daily files with earthaccess and reads them with h5py. The code looks up the HDF-EOS5 internal path by variable name.

# pip install earthaccess h5py numpy
import earthaccess
import h5py
import numpy as np

earthaccess.login()
results = earthaccess.search_data(
    short_name="OMNO2d", version="004",
    temporal=("2024-01-01", "2024-01-31"),
)
files = earthaccess.download(results[:1], "./omi")

with h5py.File(files[0], "r") as h:
    paths = []
    h.visit(lambda n: paths.append(n) if n.endswith("ColumnAmountNO2TropCloudScreened") else None)
    no2 = h[paths[0]][:].astype(float)          # (720 lat, 1440 lon), molecules cm-2
no2[no2 < -1e29] = np.nan                       # fill value -1.26765e30
print(paths[0], no2.shape, np.nanmean(no2))

Practical tips¶

• The row anomaly began on 25 June 2007 and spread in steps (May 2008, January 2009 and later); a substantial part of the swath (up to about 50% in some periods) is still affected. Always screen L2 with the row-anomaly flags (for NO2 keep pixels where XTrackQualityFlagsModified is 0 or fill; for SO2 require Flag_RowAnomaly = 0).
• Because of the row anomaly, daily global coverage has gaps since 2009. Missing cells in daily grids may be due to the anomaly rather than clouds, so check how sample counts change when building monthly means.
• The NO2 README recommends using only L2 pixels whose VcdQualityFlags least significant bit is zero. Keep negative values when averaging to avoid a systematic bias.
• For SO2 PBL columns the recommended conditions are cloud radiance fraction below 0.3, solar zenith angle below 65°, excluding edge rows (0 and 59) and excluding the South Atlantic Anomaly (Flag_SAA). Use ColumnAmountSO2_PBL or ColumnAmountSO2 for non-volcanic sources, and pick TRL, TRM, TRU or STL to match plume height for eruptions.
• The HCHO README says not to use pixels whose main_data_quality_flag is 'bad', and to take particular care with solar zenith angles above 70°, cloud fractions above 0.4, and snow or ice. Single pixels are noisy, so HCHO is usually averaged over days to a month.
• For OMTO3 (ozone) only error flags 0 (good) and 1 (glint corrected) are recommended; this screening also removes row-anomaly pixels. Flagging was tightened for the Hunga Tonga eruption period, 11–28 January 2022.
• OMI gives one early-afternoon observation. When comparing NO2, with its strong diurnal cycle, against daily means from ground monitors, match the observation time.
• The V004 collection metadata describe the data as not yet fully validated. Before trend studies, check the known issues on the GES DISC product pages and the READMEs.

Notices and change history¶

References for your paper¶

Dataset citation¶

OMNO2d V004 (L3 NO2) — DOI 10.5067/Aura/OMI/DATA3407

@misc{omno2d_v004,
  author    = {Krotkov, Nickolay A. and Lamsal, Lok N. and Marchenko, Sergey V. and Fisher, Bradford L. and Bucsela, Eric J. and Fasnacht, Zachary and Yang, Eun-Su and Qin, Wenhan and Vasilkov, Alexander and Li, Can and Joiner, Joanna and Choi, Sunny and Swartz, William H.},
  title     = {{OMI/Aura} {NO2} Cloud-Screened Total and Tropospheric Column {L3} Global Gridded 0.25 degree x 0.25 degree {V004}},
  year      = {2024},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/OMI/DATA3407}
}

OMTO3d V004 (L3 ozone and aerosol index) — DOI 10.5067/Aura/OMI/DATA3401

@misc{omto3d_v004,
  author    = {Bandel, Matthew and Haffner, David and Fasnacht, Zachary and Bhartia, Pawan K. and Li, Can},
  title     = {{OMI/Aura} {TOMS}-Like Ozone, Aerosol Index, Cloud Radiance Fraction {L3} 1 day 1 degree x 1 degree {V004}},
  year      = {2025},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/OMI/DATA3401}
}

OMSO2 V004 (L2 SO2) — DOI 10.5067/Aura/OMI/DATA2422

@misc{omso2_v004,
  author    = {Li, Can and Krotkov, Nickolay A. and Leonard, Peter and Joiner, Joanna},
  title     = {{OMI/Aura} Sulphur Dioxide ({SO2}) Total Column 1-orbit {L2} Swath 13x24 km {V004}},
  year      = {2025},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/OMI/DATA2422}
}

OMHCHO V004 (L2 HCHO) — DOI 10.5067/AURA/OMI/DATA2415

@misc{omhcho_v004,
  author    = {Gonzalez Abad, Gonzalo},
  title     = {{OMI/Aura} Formaldehyde ({HCHO}) Total Column 1-orbit {L2} Swath 13x24 km {V004}},
  year      = {2025},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/AURA/OMI/DATA2415}
}

Reference papers¶

OMI instrument paper — DOI 10.1109/TGRS.2006.872333

@article{levelt2006omi,
  author  = {Levelt, P. F. and van den Oord, G. H. J. and Dobber, M. R. and Malkki, A. and Visser, Huib and de Vries, Johan and Stammes, P. and Lundell, J. O. V. and Saari, H.},
  title   = {The ozone monitoring instrument},
  journal = {IEEE Transactions on Geoscience and Remote Sensing},
  volume  = {44},
  number  = {5},
  pages   = {1093--1101},
  year    = {2006},
  doi     = {10.1109/TGRS.2006.872333}
}

Overview of 14 years of OMI operations (including the row anomaly) — DOI 10.5194/acp-18-5699-2018

@article{levelt2018omi,
  author  = {Levelt, Pieternel F. and Joiner, Joanna and Tamminen, Johanna and Veefkind, J. Pepijn and Bhartia, Pawan K. and Stein Zweers, Deborah C. and others},
  title   = {The Ozone Monitoring Instrument: overview of 14 years in space},
  journal = {Atmospheric Chemistry and Physics},
  volume  = {18},
  number  = {8},
  pages   = {5699--5745},
  year    = {2018},
  doi     = {10.5194/acp-18-5699-2018}
}

Acknowledgements¶

GES DISC asks that each collection used be cited in the form above (authors, year, title, version, distributor, access date, DOI). Authors and years follow the CMR citation records; the creator lists registered with DataCite can differ, so confirm against the citation on the GES DISC product page. Cite Levelt et al. (2006, 2018) for the instrument.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• NASA Science — Aura mission
• NASA — Potential Evolution of the Aura Mission
• KNMI — OMI row anomaly background
• OMI Data User's Guide (GES DISC)
• KNMI — Ozone Monitoring Instrument