MIR VOC Calculations, Values, and Evaporation Rates

Posted on March 1, 2026

Think of MIR VOC like a “smog score” for cleaning liquids. Every solvent has its own score that tells us how much it can help make dirty air (called ozone). To find the MIR VOC of a mixture, we use a simple math formula that averages everything together:

{MIR}_{b l e n d} = \frac{\sum (m_{i} \times f_{V O C, i} \times M I R_{i})}{\sum (m_{i} \times f_{V O C, i})}

That looks fancy, but it just means: multiply each ingredient by how much you used and its MIR number, add those up, and then divide by only the parts that count as VOC. The answer tells you how “smog-strong” your whole blend is.

Now here’s the fun twist: some solvents are called “exempt.” That means they don’t count as VOC for air rules — even though they’re still liquids in your blend. Examples of exempt solvents are acetone, methyl acetate, and propylene carbonate. When we calculate MIR VOC, these exempt solvents act like invisible helpers: they don’t add to the smog score at all. But they also don’t lower it! They simply disappear from the VOC math. Only the non-exempt solvents get counted when we divide and calculate the final MIR.

Let’s try an example blend: 25% toluene + 25% isopropyl alcohol (IPA) + 50% acetone. We’ll use these MIR values: toluene = 4.00, IPA = 0.61, and acetone is exempt (so it counts as 0 and doesn’t go in the VOC total).

Step 1 — multiply each counted ingredient by its MIR:

Toluene $0.25 \times 4.00 = 1.00$
IPA: $0.25 \times 0.61 = 0.1525$
Acetone (exempt): $0.50 \times 0 = 0$

Add them up:

1.00 + 0.1525 = 1.1525

Step 2 — figure out how much VOC “counts”: 
Only toluene and IPA count, so that’s 25% + 25% = 50% (or 0.50).
Now divide:

{MIR}_{b l e n d} = \frac{1.1525}{0.50} = 2.305

Final MIR VOC of the blend = about 2.31 g O₃/g VOC.

So even though half the blend is acetone, it doesn’t lower the MIR — it just doesn’t count. That’s why chemists work hard to use very low-MIR solvents in their formulas: so the final smog score stays small, the air stays cleaner, and everyone can breathe easier.

Below are typical evaporation rates expressed as relative evaporation rate (RER) vs. n-butyl acetate = 1.0 at 25 °C.

Notes before you use this in formulations:

Values vary by data source and test method (ASTM D3539, etc.)
Temperature, airflow, humidity, and purity affect results
These are typical industry reference values, suitable for comparative formulation work

Very Fast Evaporating (>3.0)

Solvent	Relative Evaporation Rate (BuAc = 1.0)	MIR Value (CARB October 2nd, 2010)
Acetone (VOC Exempt)	~5.6	0.36
Methyl Ethyl Ketone (MEK)	~3.8	1.48
Methyl Acetate (VOC Exempt)	~3.1	0.07
Tetrahydrofuran (THF)	~8.0	4.31
1,3-Dioxolane	~4.0	4.96
trans-1,2-Dichloroethene	~4.5	1.7
Cyclohexane	~6.0	1.25
n-Heptane	~3.3	1.02

Fast (1.5 – 3.0)

Solvent	Relative Evaporation Rate	MIR Value (CARB October 2nd, 2010)
Ethyl Acetate	~2.8	0.63
Isopropyl Acetate	~2.3	1.07
Methanol	~3.0	0.67
Isopropyl Alcohol (IPA)	~1.7	2.51
n-Propyl Alcohol	~2.0	2.5
Ethylbenzene	~2.7	3.04
m-Xylene	~0.7	9.75
o-Xylene	~0.6	7.64
p-Xylene	~0.7	5.84
4-Methyl-2-pentanone (MIBK)	~1.6	3.88

(Note: Aromatics feel “medium” because although their RER is below 1 in some tables, they evaporate faster than many glycol ethers.)

Medium (0.5 – 1.5)

Solvent	Relative Evaporation Rate	MIR Value (CARB October 2nd, 2010)
n-Butyl Acetate	1.0 (reference)	0.83
Cyclohexanone	~0.3	1.35
Isobutyl Alcohol	~0.9	2.51
n-Butyl Alcohol	~0.3	2.88
Secondary Butyl Alcohol	~1.3	1.36
Tertiary Butyl Alcohol	~2.1	0.41
Monochlorobenzene	~0.4	0.32
Dimethyl Carbonate	~3.2	0.06
Ethyl 3-Ethoxypropionate (EEP)	~0.2	3.58
1-Methoxy-2-propanol (PM)	~0.3	2.44
1-Methoxy-2-propyl Acetate (PMA)	~0.4	1.7
2-Methoxyethyl Acetate	~0.3	1.15
2-Ethoxyethyl Acetate	~0.2	1.84

Slow (0.1 – 0.5)

Solvent	Relative Evaporation Rate	MIR Value (CARB October 2nd, 2010)
Isopropyl Acetate	~2.3 (borderline fast)	1.07
2-Butoxyethyl Acetate (EBA)	~0.1	1.62
Dipropylene Glycol Methyl Ether Acetate (DPMA)	~0.05	1.38
Glycol Ether DB Acetate	~0.04	1.38
Propylene Carbonate (VOC Exempt)	~0.01	0.28
Diisobutyl Ketone (DIBK)	~0.2	2.68
Diacetone Alcohol	~0.1	0.6
Benzyl Alcohol	~0.02	5.11
Diethyl Phthalate	~0.001	1.62

Very Slow (<0.1)

Solvent	Relative Evaporation Rate	MIR Value (CARB October 2nd, 2010)
Ethylene Glycol	~0.01	3.13
Propylene Glycol	~0.01	2.58
Glycerol	~0.0001	3.15
Diethylene Glycol	~0.005	3.35

Glycol Ethers (Typical Values)

Solvent	Relative Evaporation Rate	MIR Value (CARB October 2nd, 2010)
Glycol Ether EB (2-Butoxyethanol)	~0.08	2.9
Glycol Ether PnP (1-Propoxy-2-propanol)	~0.2	2.68
Glycol Ether PnB (Propylene Glycol n-Butyl Ether)	~0.05	2.72
Glycol Ether DPM	~0.05	1.98
Glycol Ether DM	~0.4	2.85
Glycol Ether DB	~0.02	2.39
Glycol Ether DPnB	~0.03
Glycol Ether TPM	~0.01	1.92
2-Ethoxyethanol	~0.2	3.71
1-Ethoxy-2-propanol	~0.3	3.09
2-Propoxyethanol	~0.15	3.3

Hydrocarbon Solvents

Solvent	Boiling Range (degrees F)	MIR Value (CARB October 2, 2010)
Alkanes (< 2% Aromatics) (Isohexane, Hexane)	80-205	1.42
Alkanes (< 2% Aromatics) (200-230, VM&P, Mineral Spirits, 300-360)	>205-340	1.17
Alkanes (< 2% Aromatics) 142 Flash, AGL-LVP	>340-460	0.70

Practical Formulation Insight (For You)

Since you’re working in:

VOC/MIR-driven SCAQMD environments
PCBTF replacement
Precision cleaning

You typically balance:

Fast evaporators (acetone, heptane, MEK) → quick flash
Mid-range carriers (PMA, MIBK, EEP) → solvency balance
Slow tail solvents (DBE, glycol ethers) → film leveling & soil lift

Excel Document:
• MIR Value VOC Cheat Sheet with Evaporation Rates

Disclaimer
The information presented in this blog reflects the results of our own independent online research. While we strive to provide useful and accurate insights, actual figures, details, and outcomes may vary. We do not guarantee the completeness, reliability, or accuracy of any data referenced. Readers should independently verify all details before making any business, operational, or regulatory decisions.

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