Smog Formation Potential calculator.
Estimate the photochemical smog-forming potential of VOC emissions from a chemical process, weighted by each compound's atmospheric reactivity and normalised to mass of product.
What is Smog Formation Potential — and why does it matter?
Smog Formation Potential (SFP), also called Photochemical Ozone Creation Potential (POCP), measures how much a chemical process contributes to ground-level (tropospheric) ozone and photochemical smog through its emissions of volatile organic compounds (VOCs). In sunlight, VOCs react with NOx to form ozone and other secondary pollutants; some VOCs are far more reactive than others, so a simple mass count of "VOCs emitted" hides most of the picture. SFP fixes this by weighting each VOC's emitted mass by its Maximum Incremental Reactivity (MIR) — the ozone it forms, per gram, under conditions that maximise its contribution.
The formula
| Symbol | Term | Units |
|---|---|---|
| \(\text{SFP}\) | Smog Formation Potential | g O3-eq per g product; ideal value = 0 |
| \(m_i\) | Mass of VOC species \(i\) emitted or vented from the process (not incorporated into product) | g |
| \(\text{MIR}_i\) | Maximum Incremental Reactivity of VOC species \(i\) — mass of ozone formed per mass of VOC | g O3 / g VOC |
| \(m_{\text{product}}\) | Mass of isolated desired product | g |
Only emitted VOC — solvent lost to evaporation, venting, or purge gas, not solvent recovered by distillation or condensation — contributes to SFP. Halogenated solvents (e.g. DCM) and many ketones/esters have low MIR values and are sometimes excluded from regulatory VOC counts entirely; check your jurisdiction's definition if reporting formally.
Indicative reactivity of common lab VOCs
| VOC class | Example | MIR (g O3/g VOC) |
|---|---|---|
| Alkenes | Propylene, ethylene | 9–12 (very high) |
| Aromatics | Toluene, xylenes | 4–10 (high) |
| Aldehydes | Formaldehyde, acetaldehyde | 6–8 (high) |
| Alkanes / cycloalkanes | Hexane, cyclohexane | 1–1.5 (moderate) |
| Alcohols / esters / ketones | Ethanol, ethyl acetate, acetone | < 1.5 (low) |
| Halogenated solvents | Dichloromethane | < 0.2 (very low) |
Values are illustrative, rounded from Carter's (2010) published MIR scales — see the reference table in the "VOC emissions" section below for the specific factors used by this calculator, and consult the primary literature for regulatory or publication-quality figures.
Strengths and limitations
Strengths
- Reactivity-weighted: distinguishes highly smog-forming solvents from benign ones
- Directly actionable at the solvent/reagent-selection stage of process design
- Complements CO₂-based metrics (GWP, Carbon Footprint) with a local air-quality lens
- MIR scales are peer-reviewed and used in regulatory VOC-reactivity accounting
Limitations
- MIR values depend on the ambient VOC/NOx mix and chemical mechanism used to derive them
- Does not account for NOx emissions, which co-determine actual ozone formation
- Requires an estimate of what fraction of each material is actually emitted (not just used)
- Says nothing about toxicity, global warming, or waste mass — use alongside other metrics
Smog Formation Potential in context: complementary green metrics
| Metric | What it measures | Stage |
|---|---|---|
| E-factor | Mass of all waste per mass of product (all inputs, real scale) | Experimental |
| Solvent Intensity | Mass of solvent used per mass of product | Experimental |
| GWP Horizon | How a gas's CO₂-equivalent climate impact depends on the time horizon chosen | Conceptual |
| Smog Formation Potential | Ozone-equivalent local air-quality impact of VOC emissions per mass of product | Experimental |
Experiment details
VOC emissions
Enter every VOC actually emitted or vented from the process — solvent lost to evaporation, purge/vent gas, or workup off-gassing. Do not include solvent that is recovered by condensation or distillation. Select a compound and its Maximum Incremental Reactivity (MIR) factor fills automatically; choose Custom for unlisted VOCs and enter the factor manually.
| VOC | Mass emitted (g) | MIR factor (g O3/g VOC) | O3-eq (g) |
|---|
Product output
Enter the mass of each desired product actually isolated (not theoretical yield). If your process produces multiple valuable products, add each one — their combined mass forms the denominator of the SFP.
| Product name | Mass isolated (g) |
|---|
Results
O₃-eq by VOC
Product vs. O₃-eq balance
Detailed breakdown & interpretation
| VOC | MIR factor | Mass emitted (g) | O₃-eq (g) | % of O₃-eq | Visual |
|---|---|---|---|---|---|
| Enter VOC emissions and product above to see breakdown. | |||||
Interpretation
Save & load sessions
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Export
Export your Smog Formation Potential calculation as a PDF report or CSV data file. PDF opens in a new tab and uses your browser's print function. CSV downloads directly.
Where can I read more?
References are sorted alphabetically by first author.
- P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, 1998. ISBN 978-0-19-850698-0. — Original statement of the 12 Principles.
- W. P. L. Carter, Development of ozone reactivity scales for volatile organic compounds, J. Air Waste Manag. Assoc., 1994, 44, 881–899. DOI. — Original derivation of Maximum Incremental Reactivity (MIR).
- W. P. L. Carter, Development of the SAPRC-07 chemical mechanism and updated ozone reactivity scales, Atmos. Environ., 2010, 44, 5324–5335. DOI. — Updated MIR values used as the basis for this calculator's reference factors.
- R. G. Derwent, M. E. Jenkin and S. M. Saunders, Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions, Atmos. Environ., 1996, 30, 181–199. DOI. — European POCP reactivity scale, an alternative to the US MIR scale.
- US EPA. Technical Overview of Volatile Organic Compounds. epa.gov. — Regulatory definitions of VOCs and negligibly-reactive compound exemptions.
- D. J. C. Constable, A. D. Curzons and V. L. Cunningham, Metrics to 'green' chemistry — which are the best?, Green Chem., 2002, 4, 521–527. DOI. — A good further reference for the strengths and limitations of green chemistry metrics.
Contributors
Roles follow the CRediT taxonomy (Contributor Roles Taxonomy), adapted for educational software. Hover a contributor's name for a summary, or a column header for the definition of that role.
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This portal was built with the assistance of a large language model (Claude, Anthropic), which was used to generate and refine code, articulate and structure contributed ideas within the defined page format, and support iterative design decisions. All scientific content, conceptual frameworks, pedagogical choices, and final outputs were directed, reviewed, and verified by the contributors listed above.
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