CENTRE FOR ATMOSPHERIC RESEARCH (CAR)
NATIONAL SPACE RESEARCH AND DEVELOPMENT AGENCY (NASRDA)

SCIENTIFIC PUBLIC INFORMATION & ENVIRONMENTAL SAFETY RELEASE

Akure Odour Episodes, July–August 2026

Preliminary research-based atmospheric assessment for public education, precaution and environmental protection

Prepared by Muawiya Sani | Atmospheric Physics and Air-Quality Research

PUBLIC-SAFETY PURPOSE: CAR–NASRDA is issuing this scientific information release to support public understanding, responsible precaution and environmental protection. The assessment is preliminary and does not replace direct chemical sampling or a full source-attribution investigation.

Executive Message

Available evidence indicates that the reported Akure odour episodes occurred under a highly variable atmospheric environment. Temperature, humidity, solar radiation and wind conditions changed substantially, while MERRA-2 indicated variability in PM_2.5, SO₂ and sulfate aerosol. MODIS Satellite Aerosol optical depth (AOD) also varied.

The Ondo State Government reported that the Ala River was not identified as the source and that an atmospheric pollution episode involving certain organic compounds was under investigation. The specific odorous chemical and its emission source remain unresolved.

1. Scientific Basis and Analytical Approach

This release presents a preliminary scientific investigation rather than commentary based solely on public reports. Information was assembled from the official Ondo State Ministry of Environment statement, community observations and the available Akure atmospheric datasets, then examined against time, meteorological conditions and atmospheric-composition indicators. Interpretation was cross-checked with established atmospheric-science principles concerning environmental odours and air pollution.

Community and official evidence: reported dates, locations, perceived odour characteristics and the preliminary government finding were separated from unverified public hypotheses.
Meteorology: temperature, relative humidity, solar radiation and wind speed were examined because they influence atmospheric stability, mixing, transport, dilution and near-surface persistence.
Atmospheric composition: MERRA-2 records of PM₂.₅, SO₂, sulfate aerosol, CO, total-column NO₂ and total-column ozone were considered together rather than as isolated indicators.
Aerosols: available AOD observations were treated as column-integrated aerosol information, not as direct surface PM₂.₅ or odour measurements.
Temporal comparison: periods of elevated humidity, reduced solar heating, weaker ventilation and enhanced pollutant indicators were identified for comparison with reported odour episodes, without assuming that coincidence proves causation.
Uncertainty: each indicator was assessed for what it can and cannot establish. Regional reanalysis data were not used to identify a local emission source or a specific chemical.

The approach draws on established atmospheric-aerosol and air-quality research, including satellite–ground validation of AOD, satellite-based estimation of surface PM₂.₅ using meteorological information, and integration of observations with MERRA-2 reanalysis. The assessment maintains a clear distinction between observations, model/reanalysis information and source attribution.

2. What the Ondo State Government Reported

The Ondo State Ministry of Environment press statement of 12 August 2026 reported that, following a directive from the Commissioner for Environment, professionals working with environmental consultants were constituted to investigate the possible source and nature of the odour. The preliminary finding was that the Ala River course was not identified as the source, contrary to earlier speculation.

The statement described the episode as air pollution associated with the release of certain organic compounds into the atmosphere and indicated that work was continuing to identify the specific compounds, their characteristics and their source. Residents were advised to limit exposure, use nose masks in affected areas, and report suspicious activities, illegal waste disposal, unusual emissions and other environmental violations.

3. What Residents Reported

Public observations describe the odour variously as sewage-like, chemical-like or rotten-egg-like, with reports from several parts of Akure and stronger perception during evening, nighttime or early-morning periods. Suggested explanations included waste-disposal sites, abattoirs, sewage or stagnant water, industrial emissions and unidentified chemical releases. Some comments also raised concerns about possible illicit chemical activity.

These are community hypotheses, not established sources. Their scientific value is that they provide approximate time, location, duration and perceived characteristics that can be tested against wind direction, chemical measurements and atmospheric transport.

A rotten-egg description is compatible with hydrogen sulfide (H₂S), but it does not establish H₂S as the cause. Direct ambient-air measurement or chemical sampling is required to reach such a conclusion.

4. Key Atmospheric Findings

The meteorological dataset indicates temperatures of approximately 22.4–29.1 °C, relative humidity of 61.8–91%, and wind speeds of 0.7–5.0 m s⁻¹. Solar radiation showed a strong day–night cycle, reaching about 903 W m⁻² on 7 July at 11:30. These conditions affect boundary-layer development, atmospheric mixing, transport and dilution.

High relative humidity occurred during several periods, including approximately 86.5% on 17 July, 82.5% on 2 August, 80.5% on 15 July and 79.5% on 9 July. Such conditions may influence atmospheric stability and aerosol water uptake, but high humidity alone cannot identify an odorous compound or source.

Wind speed varied substantially. Weak-wind periods can reduce horizontal ventilation and favour persistence of locally emitted pollutants, whereas stronger winds can enhance transport and dilution. Wind direction remains particularly important for source attribution because it indicates the likely upwind source sector.

5. Nighttime and Early-Morning Conditions

After sunset, loss of solar heating and surface cooling can favour a more stable and shallower near-surface mixing environment. Under suitable conditions, an emitted odorous compound may therefore remain near the surface for longer. However, the available data do not show that wind speed was consistently lower at night. Nighttime and early morning should therefore be treated as periods for focused comparison, not as proof of a nighttime emission source.

6. Aerosol Optical Depth (AOD)

Clearly dated AOD observations include 0.160 on 1 July, 0.289 on 4 July, 0.395 on 7 July and 0.114 on 7 August. The variation indicates changes in the broader column aerosol burden. AOD is a column-integrated optical quantity and is not equivalent to surface PM₂.₅ or a direct odour fingerprint.

7. Sulfur Indicators: SO₂ and SO₄

The MERRA-2 SO₂ series shows pronounced sub-daily variability. On 1 July, reported values ranged from approximately 1.12×10⁻¹⁰ to 4.09×10⁻¹⁰ kg m⁻³, while the 2 July maximum was approximately 5.47×10⁻¹⁰ kg m⁻³. These values provide regional atmospheric context and do not demonstrate that SO₂ caused the odour.

Selected SO₄ surface-mass values ranged from 4.89×10⁻¹⁰ kg m⁻³ on 1 July to 1.37×10⁻¹⁰ kg m⁻³ on 17 July. Sulfate represents particulate aerosol rather than an odorous gas. The SO₂–SO₄ relationship is therefore useful for examining sulfur-related atmospheric processing, but it does not establish a local odour source.

8. PM₂.₅, CO, NO₂ and O₃

The MERRA-2 PM₂.₅ record shows substantial sub-daily variability. PM₂.₅ is a mixture of fine particles and is not itself a specific odorous chemical. With a horizontal resolution of roughly 0.625° × 0.5° (about 50 km), MERRA-2 provides regional atmospheric context rather than direct measurement at an affected street or neighbourhood.

CO values were approximately 86.9–136.2 Mole, with a mean of 106.2 Mole. The units and measurement method should be stated explicitly before these values are used for exposure assessment. CO is colourless and odourless; changes in CO alone cannot explain the perceived smell. Total-column NO₂ ranged approximately 0.085–0.230 DU, while total-column ozone (O₃) ranged approximately 275–297 DU. These are column quantities, not surface breathing-level concentrations.

9. Evidence: What the Analysis Can and Cannot Establish

Evidence examined	What it contributes	What it does not prove
Meteorology	Atmospheric mixing, ventilation, transport and persistence conditions	Identity or location of an emission source
AOD	Broader column aerosol loading	Surface PM₂.₅ concentration or odour cause
MERRA-2 SO₂	Regional sulfur-gas variability	That SO₂ caused the odour or came from a specific site
MERRA-2 SO₄	Sulfate aerosol / particulate sulfur context	An odorous sulfate gas
MERRA-2 PM₂.₅	Regional fine-particle environment	A specific odorous chemical
CO, total-column NO₂ and O₃	Additional atmospheric-composition context	Local source attribution without suitable surface data
Community reports	Timing, location and perceived odour characteristics	Chemical identity or source
Government preliminary finding	Ala River not identified as source; organic compounds under investigation	The specific organic compound or emission source

10. Integrated Scientific Interpretation

The most informative approach is to identify periods when several independent indicators change together and compare them with verified odour reports. Elevated humidity, weak ventilation, low solar heating and enhanced pollutant indicators may create conditions favourable to near-surface persistence, while stronger solar heating and winds may promote mixing and dilution. Neither pattern proves the presence or absence of an odorous emission; its value lies in testing temporal and spatial consistency.

The evidence supports an atmospheric investigation involving variable dispersion conditions, aerosol loading and sulfur-related indicators, while the Ondo State Government’s preliminary statement points specifically to unidentified organic compounds. None of the available datasets, individually or collectively, currently identifies the chemical responsible or proves the local emission source.

11. Priority Actions for Further Investigation

Georeference every odour report by date, time, location, duration, intensity and perceived direction.
Add wind direction and produce wind roses and pollution roses for reported odour and pollutant episodes.
Compare odour and non-odour periods using PM₂.₅, SO₂, SO₄, CO, NO₂, O₃, temperature, relative humidity, solar radiation and rainfall.
Conduct targeted ambient-air sampling for potentially odorous compounds, including VOCs and reduced-sulfur compounds such as H₂S where scientifically justified.
Use boundary-layer height, atmospheric stability and back-trajectory analysis to test whether affected locations were repeatedly downwind of a common source sector.
Investigate suspected waste, wastewater, industrial or other emission locations independently using chemical, spatial and meteorological evidence.
Where possible, deploy calibrated or reference-grade instruments close to affected communities during future episodes so that source attribution can be based on surface observations rather than regional reanalysis alone.

12. Public Health and Precautionary Advice

Odour perception and toxicity are not the same thing. The health significance of an air pollutant depends on its identity, concentration, exposure duration and individual susceptibility. A strong smell does not by itself establish a toxic exposure, while some hazardous pollutants may be odourless.

Residents should follow official environmental and public-health advice, limit exposure during confirmed episodes where advised, and document recurring events accurately by recording the time and location. Reports of unusual emissions, illegal waste disposal or other environmental violations should be communicated through appropriate official channels.

13. Scientific Conclusion

The preliminary investigation demonstrates that the Akure odour episodes can be examined scientifically through the integration of community observations, official environmental findings, meteorological conditions, aerosol information and atmospheric-composition data. The analysis identifies atmospheric conditions capable of influencing pollutant persistence and transport, but it does not establish the specific odorous chemical or its source.

The most defensible current conclusion is that a recurring atmospheric pollution episode was reported and requires direct chemical sampling, spatial analysis and meteorological source–receptor analysis for conclusive attribution.

CAR–NASRDA PUBLIC INTEREST COMMITMENT: This release is issued in the public interest to strengthen scientific awareness, support responsible precaution, and contribute to efforts to protect lives, the environment and ecosystems. It should be read alongside official government environmental and public-health guidance as further investigations continue.

14. References and Source Notes

Ondo State Government, Ministry of Environment. “Ondo State Government Provides Update on Offensive Odour.” Press statement dated 12 August 2026. Supplied image used as the primary government source.
NASA Global Modeling and Assimilation Office (GMAO). MERRA-2: Modern-Era Retrospective Analysis for Research and Applications, Version 2; system characteristics and documentation.
NASA GMAO. MERRA-2 FAQ: PM₂.₅ formulation and sulfate-ion conversion information.
World Health Organization. Ambient (outdoor) air pollution and health; air-quality and health information.
World Health Organization. Global Air Quality Guidelines for PM₂.₅, PM₁₀, O₃, NO₂, SO₂ and CO (2021).
Agency for Toxic Substances and Disease Registry (ATSDR). Hydrogen Sulfide and Carbonyl Sulfide ToxGuide; environmental odours and related environmental-health information.
Community/public observations: summaries supplied for this assessment. These are treated as non-validated reports and hypotheses, not as evidence of a source.

Data Limitation

This release is a preliminary research-based assessment using acquired data and selected available records. It does not replace a full source-attribution investigation based on complete raw hourly datasets, wind direction, boundary-layer information, georeferenced complaints and direct chemical measurements. No plot is included because the available summary values do not provide sufficiently complete continuous time series for plots that would add meaningful scientific information.