Sulfur dioxide (SO₂) in the yard and garden
Moderate risk for your yardSO₂ is a WHO and EPA criteria air pollutant; primary source is combustion of sulfur-containing fossil fuels (coal, oil) in power plants and industrial processes, and volcanic emissions. IARC has not classified SO₂ as a carcinogen. Primary mechanism: SO₂ dissolves in airway moisture to form sulfurous and sulfuric acid, causing bronchoconstriction and mucous membrane irritation. WHO 24-hour guideline: 40 μg/m³; EPA 1-hour NAAQS: 75 ppb. SO₂ is also used as a food preservative (E220; sulfites in wine, dried fruit, processed seafood) — causes reactions ranging from flushing/hives to anaphylaxis in sulfite-sensitive individuals (~1% of general population, ~5% of asthmatics). US ambient air quality has improved substantially since the 1970s Clean Air Act.
What is sulfur dioxide (so₂)?
The IUPAC name is sulfur dioxide.
Also known as: sulfur dioxide, sulphur dioxide, Sulfurous anhydride, Sulfurous oxide.
- IUPAC name
- sulfur dioxide
- CAS number
- 7446-09-5
- Molecular formula
- O2S
- Molecular weight
- 64.07 g/mol
- SMILES
- O=S=O
- PubChem CID
- 1119
Risk for people, pets,
Moderate riskSO₂ is a WHO and EPA criteria air pollutant; primary source is combustion of sulfur-containing fossil fuels (coal, oil) in power plants and industrial processes, and volcanic emissions. IARC has not classified SO₂ as a carcinogen. Primary mechanism: SO₂ dissolves in airway moisture to form sulfurous and sulfuric acid, causing bronchoconstriction and mucous membrane irritation. WHO 24-hour guideline: 40 μg/m³; EPA 1-hour NAAQS: 75 ppb. SO₂ is also used as a food preservative (E220; sulfites in wine, dried fruit, processed seafood) — causes reactions ranging from flushing/hives to anaphylaxis in sulfite-sensitive individuals (~1% of general population, ~5% of asthmatics). US ambient air quality has improved substantially since the 1970s Clean Air Act.
Regulatory consensus
13 regulatory and scientific bodies have classified Sulfur dioxide (SO₂). The classifications differ — that's the data.
| Agency | Year | Classification | Notes |
|---|---|---|---|
| WHO | — | criteria air pollutant | |
| US EPA | — | criteria air pollutant | |
| IARC | — | not classified as a carcinogen | |
| EPA CTX / IARC | — | Group 3 - Not classifiable as to its carcinogenicity to humans | |
| EPA CTX / Genetox | — | Genotoxicity: positive (Ames: None, 3 positive / 1 negative reports) | |
| EPA CTX / Genetox | — | Genotoxicity: positive (Ames: None, 3 positive / 1 negative reports) | |
| EPA CTX / Skin-Eye | — | Skin Irritation: Skin Corr. 1B (score: very high) | |
| EPA CTX / Skin-Eye | — | Skin Irritation: Skin corrosion/irritation - Category 1 (score: very high) | |
| EPA CTX / Skin-Eye | — | Eye Irritation: Category 2A (score: high) | |
| EPA CTX / Skin-Eye | — | Eye Irritation: Eye Dam. 1 (score: very high) | |
| EPA CTX / Skin-Eye | — | Skin Irritation: Skin Corr. 1B (score: very high) | |
| EPA CTX / Skin-Eye | — | Eye Irritation: Category 8.3A (Category 1) (score: very high) | |
| EPA CTX / Skin-Eye | — | Skin Irritation: Category 8.2B (Category 1B) (score: very high) |
Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.
Where your yard encounter sulfur dioxide (so₂)
- Outdoor Air — Vehicle exhaust, Industrial emissions, Power plant discharge
- Indoor Air — Combustion byproducts, Office buildings, Parking garages
Safer alternatives
Lower-risk approaches that achieve a similar outcome to Sulfur dioxide (SO₂):
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Physical/mechanical pest control (IPM)
Trade-offs: More labor-intensive. May not be sufficient for severe infestations.Relative cost: 1.2-2×
Frequently asked questions
Is sulfur dioxide (so₂) safe for your yard?
SO₂ is a WHO and EPA criteria air pollutant; primary source is combustion of sulfur-containing fossil fuels (coal, oil) in power plants and industrial processes, and volcanic emissions. IARC has not classified SO₂ as a carcinogen. Primary mechanism: SO₂ dissolves in airway moisture to form sulfurous and sulfuric acid, causing bronchoconstriction and mucous membrane irritation. WHO 24-hour guideline: 40 μg/m³; EPA 1-hour NAAQS: 75 ppb. SO₂ is also used as a food preservative (E220; sulfites in wine, dried fruit, processed seafood) — causes reactions ranging from flushing/hives to anaphylaxis in sulfite-sensitive individuals (~1% of general population, ~5% of asthmatics). US ambient air quality has improved substantially since the 1970s Clean Air Act.
What products contain sulfur dioxide (so₂)?
Sulfur dioxide (SO₂) appears in: Vehicle exhaust (Outdoor air); Industrial emissions (Outdoor air); Combustion byproducts (Indoor air); Office buildings (Indoor air).
Why do regulators disagree about sulfur dioxide (so₂)?
Sulfur dioxide (SO₂) has been classified by 13 agencies including WHO, US EPA, IARC, EPA CTX / IARC, EPA CTX / Genetox, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.
See Sulfur dioxide (SO₂) in the outdoor app
Look up products containing sulfur dioxide (so₂), compare to alternatives, and explore the full data record.
Open in outdoor View raw API dataSources (3)
- US EPA National Ambient Air Quality Standards for Sulfur Dioxide (2010) — regulatory
- WHO Air Quality Guidelines for Sulfur Dioxide (Global Update 2021) (2021) — regulatory
- ATSDR Toxicological Profile for Sulfur Dioxide (1998) — report
Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →