What is Smog Formation Potential — and why does it matter?

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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 NO_x 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.

GoalMinimise ozone-equivalent (O₃-eq) emissions per unit of desired product, since an ideal SFP of zero means no smog-forming VOCs are released at all.

WhyGround-level ozone damages respiratory health, reduces crop yields, and is a criteria air pollutant regulated in most jurisdictions — unlike CO₂, its impact is local and immediate.

HowSubstitute high-MIR solvents and reagents (aromatics, alkenes) for low-reactivity alternatives, capture and recover VOCs (condensers, carbon traps), and minimise venting during charging, transfer, and workup.

The formula

$$\text{SFP} = \frac{\sum_i m_i \times \text{MIR}_i}{m_{\text{product}}}$$

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/NO_x mix and chemical mechanism used to derive them
Does not account for NO_x 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 (Global Warming Potential)	CO₂-equivalent climate impact of inputs and energy	Experimental
Smog Formation Potential	Ozone-equivalent local air-quality impact of VOC emissions per mass of product	Experimental

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Experiment details

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Experiment / reaction name

Researcher(s)

Date

Lab / institution

Reaction type

Solvent

Temperature

Catalyst / additive

Reference / DOI

Notes

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VOC emissions

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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.

Indicative MIR factors (g O₃/g VOC, rounded from Carter 2010): propylene ≈ 11.7 · toluene ≈ 4.0 · xylenes ≈ 7.8 · formaldehyde ≈ 7.2 · acetaldehyde ≈ 6.4 · benzene ≈ 0.72 · n-hexane ≈ 1.24 · methanol ≈ 0.67 · ethanol ≈ 1.5 · acetone ≈ 0.36 · ethyl acetate ≈ 0.65 · THF ≈ 3.0 · dichloromethane ≈ 0.14

VOC	Mass emitted (g)	MIR factor (g O₃/g VOC)	O₃-eq (g)

Σ O₃-eq — g numerator of SFP

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Product output

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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)

Σ Product mass — g denominator of SFP

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Results

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Smog Formation Potential

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g O₃-eq / g product

Total O₃-eq

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grams

Total Product

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grams isolated

Total VOC Emitted

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grams

SFP scale (lower is better — indicative thresholds)

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0 (ideal)0.528+

O₃-eq by VOC

Product vs. O₃-eq balance

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Detailed breakdown & interpretation

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VOC	MIR factor	Mass emitted (g)	O₃-eq (g)	% of O₃-eq	Visual
Enter VOC emissions and product above to see breakdown.

Interpretation

Enter your VOC emissions and product mass above to generate an interpretation.

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Save & load sessions

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Sessions are stored in your browser only. No data leaves your device.

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Export

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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.

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Where can I read more?

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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.

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Contributors

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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.

Contributor

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.

Whilst every effort has been taken to ensure accuracy, mistakes can happen. If you notice something that doesn’t look quite right, kindly reach out to the DodecaGreen team via the Contact page.

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How do I cite this page?

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If you use this tool in teaching or published work, please cite the DodecaGreen portal as the source.

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Smog Formation Potential calculator.