Determining the VOC Content

Calculating Volatile Organic Compound (VOC) Content of a Material

There is sometimes confusion over the terms VOC of coating/colorant/adhesive and VOC of material. The VOC of coating/colorant/adhesive is the same as the term “regulatory VOC,” which is equivalent to the term "VOC, less water and exempts." The VOC of material is the same as the term "actual VOC," which is equivalent to the term "VOC, including water and exempts."

The regulatory VOC calculates the VOC less exempts and water, which is a more complicated calculation than the actual VOC, in that it subtracts the volume of water and the volume of exempt compounds from the volume of material, in the denominator. The calculation was derived to express the VOC emitted per volume of coating solids to eliminate the effect of dilution. Dilution with water or exempt solvents would reduce the VOC-to-paint-volume ratio while maintaining a constant VOC-to-paint/adhesive-solids ratio. This is important because those materials are applied at a certain film thickness so dilution would result in a larger volume of the material being applied to achieve the same film thickness. For conventional solvent based products with no exempt compounds, the two values are always the same.

For waterborne coatings and coatings containing exempt compounds, the VOC of coating is always the higher of the two values. The VOC limits listed in the Table of Standards (PDF, 35kb) refer to the VOC of coating. The only exception is for low solids coatings where the purpose of the coating is not to build film thickness. Low solids coatings, which are defined as coatings containing less than one pound of solids per gallon of coating, are regulated by the VOC of material. VOC emissions, including the emissions fee in Rule 314, are also calculated based on the VOC of material.

The VOC Calculator (XLS, 90kb) is a spreadsheet that will calculate both VOC values based on the solids, water content and density of the material. 

Sample Coating Calculation:

Density= 0.99 g/mL
Water= 50% by weight
Density of water= 0.997 g/mL
Solids= 48% by weight

VOC of Coating Calculation
(Regulatory VOC, less water and exempt compounds):
 
Remove the volume solid from denominator
 Volume Solids= [Weight Solids]/[Density]

VOC of Material Calculation (Actual VOC):

What are Maximum Incremental Reactivity Based VOC Limits?

Maximum Incremental Reactivity (MIR) is a way to measure how much a specific volatile organic compound (VOC) contributes to the formation of ground-level ozone, commonly known as smog. Not all VOCs react in the atmosphere the same way. Some VOCs are more likely to form ozone than others, even if they are emitted in the same amount.

Traditional mass-based VOC limits usually regulate products based on the total mass of VOCs present, such as grams of VOC per liter of product. Under that approach, all VOCs are treated the same, other than exempt compounds, regardless of their reactivity. MIR accounts for the varying chemical reactivities of individual compounds, with each compound assigned an MIR value that reflects how much it contributes to ozone formation under high reactivity atmospheric conditions.

MIR-based VOC limits allow regulations to better control the ozone impacts from product emissions. Instead of focusing only on how much VOC is present, this approach also considers what types of VOCs are being emitted. As a result, products formulated with lower reactivity compounds may have a lower overall ozone forming impact, even if their total VOC content is higher. This method of regulating VOC limits can be used alongside mass-based limits to provide more flexibility to manufacturers as limits are lowered or toxic solvents are prohibited. Each compound is assigned an MIR value assigned by the California Air Resources Board and can be found on their Tables of Maximum Incremental Reactivity (MIR) Values.

Determining the Product-Weighted MIR Value of a Product

The MIR value of an individual compound represents that compound’s relative ozone-forming potential. The MIR value of a finished product is usually determined by calculating the product-weighted MIR (PW-MIR), which accounts for the amount and reactivity of each ingredient in the formulation.

For a coating, the MIR value is determined using the product formulation. Each ingredient in the product is identified, the weight fraction of each ingredient is determined, and each reactive organic compound is assigned an MIR value. The MIR value for each compound is then multiplied by the weight fraction of that ingredient in the product. The individual weighted MIR values are added together to determine the PW- MIR.

Staff is developing a PW-MIR Calculator (forthcoming), which is a spreadsheet designed to assist calculating the PW-MIR.

After determining the PW-MIR, that value is compared to the applicable Rule’s Alternative MIR Limits. A list of current Alternative MIR Limits can be accessed HERE.

The general calculation for PW-MIR is:

The weight fraction is the weight of an ingredient divided by the total weight of the coating. For example, if a product contains 20 grams of a solvent in a 100 gram formulation, the weight fraction of that solvent is 0.20. If that solvent has an MIR value of 1.50, the weighted MIR contribution of that ingredient would be:

This same process is repeated for each ingredient in the product. Ingredients with higher MIR values or higher weight fractions will contribute more to the overall product-weighted MIR. Ingredients with low MIR values, or ingredients present in very small amounts, will have a smaller effect on the final result.

For example, a simplified product formulation may contain the following ingredients:

In this example, the PW-MIR would be 0.96 grams of ozone formed per gram of product.

For compounds with unassigned MIR values or Test Methodology questions, please contact:

Dr. David Cocker
Profess & Chair
Chemical Environmental Engineering Dept
David.Cocker@ucr.edu
(951) 827-2408

Guidance on VOC Labeling and Test Methods for Coatings

Coatings products sold or used within South Coast AQMD's jurisdiction may be required to include VOC content on product labels pursuant to Rule 443.1 ─ Labeling of Materials Containing Organic Solvents. VOC content for labeling purposes may be determined by calculation from formulation data and/or by test results. The approved VOC test methods appropriate for determining product VOC content, whether for labeling or compliance purposes, vary by coating application. Please refer to the specific VOC rule applicable to the coating product to identify the required test methods and VOC calculation procedures. Further information on VOC test methods is available at: https://www.aqmd.gov/home/rules-compliance/compliance/vocs/architectural-coatings/current-and-past-activities/working-group.

For energy-curable coatings, VOC content may be determined using ASTM D5403 ─ Standard Test Methods for Volatile Content of Radiation Curable Materials, which is an approved method for establishing VOC content for both labeling and compliance purposes. However, thin-film energy-curable coatings (including UV/EB/LED-cured materials applied with very low film thickness) currently do not have an approved compliance test method for determining VOC content under South Coast AQMD rules. When VOC content must be included on product labels pursuant to Rule 443.1, manufacturers may use formulation data or estimate the VOC emissions of the reactive components of the thin film energy curable coatings using ASTM D7767 ─ Standard Test Method to Measure Volatiles from Radiation Curable Acrylate Monomers, Oligomers, and Blends and Thin Coatings Made from Them. ASTM D7767 is not a U.S. EPA approved test method and as such is not an appropriate compliance test method that a third-party laboratory, or the South Coast AQMD Laboratory, could rely on to verify the VOC content of a thin-film energy curable coating. For determining compliance with VOC limits for thin-film energy-curable coatings, manufacturers may rely on formulation data and ASTM D7767 to determine product VOC content for labeling purposes.