Aerosols
Why Tehran AOD and visibility move opposite seasons
Open access · cc by · source: Europe PMC
Winter mountain trapping cuts visibility while column AOD is lowest; summer dust raises AOD even as surface visibility recovers.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
This library holds 6 empirical papers on aerosols with measured outcomes rather than reviews.
Evidence for the claim as stated.
Winter mountain trapping cuts visibility while column AOD is lowest; summer dust raises AOD even as surface visibility recovers.
Evidence for the claim as stated.
Over Tehran, winter satellite AOD is a minimum while Mehrabad visibility is worst (6.3–6.8 km) because Alborz blocking traps urban aerosol near the ground, below what the column retrieval emphasises. Summer AOD rises with dust and dry weather. Friday visibility anomalies and post-rain clearing show local emissions plus wet scavenging — signals a column product alone would invert.
Evidence for the claim as stated.
Column AOD and near-surface visibility can move in opposite seasons. Tehran’s winter AOD minimum coincides with the worst Mehrabad visibility (6.3–6.8 km) because aerosol is trapped in a shallow layer; SE US MAIAC maps still track EPA monitors at R² 0.71–0.85 because that retrieval is statistically calibrated to surface PM2.5. Calling both ‘satellite aerosol’ hides whether the product is a column or a ground-trained map.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Column AOD and near-surface visibility can move in opposite seasons. Tehran’s winter AOD minimum coincides with the worst Mehrabad visibility (6.3–6.8 km) because aerosol is trapped in a shallow layer; SE US MAIAC maps still track EPA monitors at R² 0.71–0.85 because that retrieval is statistically calibrated to surface PM2.5. Calling both ‘satellite aerosol’ hides whether the product is a column or a ground-trained map.
Discoveries this paper informs or conflicts with
- Fine-particle pollution fell about 20% in the southeastern US — measured from orbit
This paper informs this development.
Study at a glance
- Design
- Other — Multi-sensor satellite, surface visibility, and trajectory/speciation synthesis for Tehran aerosols
- N
- 2000–2009 multi-year characterization; not a discrete sample-size study
- Population
- Greater Tehran Area aerosol column and surface visibility (Mehrabad)
- Outcome
- Seasonal AOD vs visibility contrast under mountain trapping and summer dust
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Why Tehran AOD and visibility move opposite seasons
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Surrounding mountains extend to over 5000 m.
Air pollution problems are exacerbated in this major metropolitan area due to surrounding mountains, which extend to over 5000 m and inhibit ventilation of pollutants, especially during wintertime.
Mehrabad winter visibility minima are 6.3 km in December and 6.8 km in January.
Mehrabad also follows the same annual pattern; however, the visibilities are systematically lower for all months with a considerable reduction during the winter with minima of 6.3 km in December and 6.8 km in January.
Key findings
Alborz blocking traps winter urban aerosol near the ground (Mehrabad visibility minima 6.3–6.8 km) while satellite AOD is minimum. Summer AOD rises with dust and dry weather. Friday visibility anomalies and post-rain clearing show local emissions plus wet scavenging.
Methodology
Authors combined 2000–2009 MODIS/MISR/TOMS/OMI aerosol retrievals, Mehrabad visibility and meteorology, HYSPLIT trajectories, fire radiative power, and GOCART speciation around Tehran.
Limitations
No in-situ chemical speciation time series inside Tehran; GOCART is 2°×2.5°, and visibility north of the Alborz can reflect fog/rain rather than aerosol.
Related papers in this topic
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