Understanding and Using the PCRC Emissions Calculator

Every paint, even powder, contains two kinds of components, that end up in two different places.  The parts you want (the "solids") end up on what you are painting.  The rest (the liquids, or "volatiles") end up in the air.  As a painter, you may not be immediately interested in what happens to the volatiles once they have floated off.  But some volatiles (the so-called volatile organic compounds, or "VOCs") contribute to air pollution, and some volatiles (the hazardous air pollutants, or "HAPs") are known to be particularly toxic.  So whether or not you're paying much attention to the volatiles, you should be aware that the environmental regulatory agencies are.

That is why there are regulations that limit the amount of VOCs or HAPs that you are permitted to release.  In order to determine whether you are operating within those limits, you are asked to calculate the VOC or HAP content of the paints you use.  But the calculations can be somewhat complicated.

The PCRC has developed the Emissions Calculator to help you through those calculations.  If you are not familiar with the ideas behind emissions calculations, please read this guide.  It is intended to help you understand the thinking behind the regulations, and to show why some of the complications are unavoidable if the regulations are to be applied fairly and effectively.

While we have tried to provide the basics in this quick overview, please note that there are special cases that are not covered here.  For a more detailed understanding of these issues, you may want to take advantage of the various resources and training opportunities that are available on this topic. 

Also, note that this guide is based on federal regulations.  You may also be subject to state or local regulations which may be different from, and in some cases more stringent than, the federal regulations.  See the State Regulations Locator to find the names of assistance providers that you can contact for more information.

Contents

1. Introduction -- How Much Pollution in that Paint?
2. VOCs or HAPs per gallon of paint
3. VOCs or HAPs per gallon of paint, less water (and "non-VOC" or "non-HAP" solvents)
4. VOCs per gallon of solids
5. VOCs per weight of solids
6. What solvents are considered "non-VOC" solvents?
7. List of coatings MACTs and corresponding measurements

Introduction -- How Much Pollution in that Paint?

How do you measure the environmental impact of a paint?  That seems like a straightforward enough question.  But the answer is not always obvious.  Suppose paint "A" contains 70% volatiles, while paint "B" contains 65%.  You might think that paint "B" is preferable environmentally.  But what if the solvents in "A" are relatively harmless, while the solvents in "B" are hazardous?  Or what if, despite the solids content, it takes twelve gallons of "B" to do the job that ten gallons of "A" can do?  What is the right way to compare one paint with another?

The short answer is that there is no one "right" way.  There are several alternative methods of measuring the VOC or HAP content of paint, and each method has advantages and disadvantages.  EPA has chosen to use different methods to apply to different cases.  The method you need to use to measure the VOCs or HAPs in the paint you are using can depend on who you are, on what you are painting, and even (in some cases) on why you are painting it.  In this section, we will outline the various methods that are in use, and try to provide a sense for the reasoning behind them.

The basic methods are:

or HAPs per gallon of solids
• VOCs or HAPs per weight of solids

Once you have read through the guide, you should be able to determine which calculation method applies to your situation.  At the end of each section, we have included a link to the appropriate PCRC Emissions Calculator input form.

VOCs or HAPs?

Older air quality regulations typically measured the amount of VOCs released by a coating, since the main concern was ozone forming potential.  Newer regulations (including all of the surface coating regulations that have come into effect since 2002) are instead written in terms of HAPs. 

If the regulations that apply to your case specify VOCs, you will find that most paint solvents besides water are in that category.  The exceptions are discussed in the section "What solvents are considered "non-VOC" solvents?" below.

If the regulations applying to you specify HAPs, you can find a convenient list of HAPs on the EPA website.  For additional information, you can find links to descriptions of known health effects for many of the HAP compounds at the "Health Effects Notebook for Hazardous Air Pollutants" page, also on the EPA website.

Note that the air quality regulations that focus on HAPs specify "organic HAPs".  Some HAPs are not organic compounds, and so they would not fit under that definition.  But in most cases, the HAPs found in paint formulations are organic, and should be included in the totals.

Which MACT?

Clean air rules have been written for specific situations, and you may need to determine which situation fits your specific case.  Some rules apply to specific industry sectors (such as aerospace or automotive), Other rules apply to specific processes that can be used by companies in many different industry sectors.  Still other rules apply to specific materials being painted (miscellaneous metal parts, or miscellaneous plastic parts are examples).

The rules are referred to collectively as NESHAP or MACT rules.  NESHAP stands for "National Environmental Standards for Hazardous Air Pollutants", and MACT stands for "Maximum Achievable Control Technology".  You can find more information on the regulatory background at the EPA website.  A useful introductory summary specifically directed toward the coatings rules can be found on the Coatings and Composites Coordinated Rule Development (CCCR) page.

In the following sections, we will look at each of these methods in enough detail for you to understand the thinking behind them, their advantages and disadvantages, and formulas used to calculate the final result.  We also provide a reference table listing all of the federal air quality ("MACT") regulations that apply to coatings processes, together with the emissions measurement method specified by each regulation.

VOCs or HAPs per gallon of paint

Perhaps the most straightforward approach to calculating VOC or HAP content can be applied to paints whose volatiles are all VOCs, or are all HAPs.  First, determine which type of pollutant (VOC or HAP) applies in your case.  Then refer to the corresponding section below.

VOCs

To measure the amount of VOCs for paints in which all the volatiles in its formulation count as ozone precursors, the most common method is to take the combined weight of all the volatiles in each gallon of paint, using simple addition to combine the weights of the individual components.  That's all there is to it.  The regulatory number is just the total weight of the volatiles in one gallon of the paint, divided by one gallon.  The unit of measurement is therefore simply pounds VOC per gallon.  The weight of the VOCs per a specific volume of the paint should be available on the paint label.

Note that no attempt is made to compare the relative ozone-generation potential of one VOC with another.  For the purposes of this calculation, all VOCs are considered to contribute equally, pound for pound, to the final result.  While this may not be the most scientific way to proceed, it greatly simplifies the calculations.

HAPs

If all of the volatile solvents in the paint are HAPs, the method proceeds exactly as with VOCs.  Add the weights of all the HAP volatiles in one gallon of paint, divided by one gallon.  The weights of HAP solvents in the paint should be available (either on the label, the Material Safety Data Sheet, or MSDS, supplied by the paint, or from the manufacturer).  Use the EPA list to check whether a particular solvent is a HAP.  If the paint solvents are a mixture of HAPs and non-HAPs, and if the MACT applying to your operation specifies HAPs per gallon of coating, use the method in the following section.

Here is the formula written out.  (In this simple case, there is really nothing to calculate, aside from adding up the totals.)

HAPs emitted per gallon of coating  align="center" class="body10" style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px">total weight of HAPs per gallon

VOC Calculator 1  You can use Calculator 1 to total the VOCs or HAPs in the formulation -- just leave the value for the water content at 0 if you are using a formulation that contains no water.  If your formulation does contain water, or another non-VOC or non-HAP solvent, see the next section.

VOCs or HAPs per gallon of paint, less water (and "non-VOC" or "non-HAP" solvents)

As mentioned in the Introduction, the older regulations were concerned with VOCs, while the newer ones have been written with the focus on HAPs.  The calculation methods are very similar.  The description below is written in terms of VOCs, but the formulas apply if everything applying to VOC solvents below is taken simply to apply to HAP solvents.

Some paint solvents are kinder to the environment than others.  Water is the primary example of a liquid whose environmental release causes no problems.  Other solvents, such as acetone, have been shown to be less harmful at low concentrations in the atmosphere, because they do not significantly contribute to ozone formation.  (See  "What solvents are considered "non-VOC" solvents?" below.)  It's definitely environmentally preferable to use less harmful solvents whenever possible, and the regulations should encourage it.

But there is a problem in using the simple "VOC per gallon of paint" method, as described in the preceding section, to measure the environmental impact of a paint that contains both VOC and non-VOC liquids.  Here's how it works:

Suppose you've got a paint formulation that exceeds the allowable VOC content, if measured in pounds of VOCs per gallon of paint.  But suppose further that the paint can tolerate a certain amount of water (or of some other non-VOC, such as acetone).  You (or the paint manufacturer) could simply thin down the paint with those non-VOC materials, until the VOCs per gallon number fell below the limit.  Now you're in compliance, but is the environment any better off?.  One gallon of the thinned paint would indeed contain less VOC content, but it would also have a lower solids content.  As a result, you would have to use more gallons of the thinned paint to build up the same thickness of coating on the part you are painting than if you were using the original formulation.  You would wind up emitting the same amount of VOCs to do the job, since the ratio of VOCs to solids hasn't changed.  You have been brought magically into compliance simply by thinning down your paint, but the environment is no better off.   This is not the outcome that the regulations are intended to bring about.

To prevent this undesirable outcome, the regulations can adopt several methods.  One of them, the "VOCs per gallon of paint, less water" method, is the topic of this section.  Other alternatives are discussed in the following sections.

The "VOCs per gallon of paint, less water" method is a bit trickier to explain than the other methods.  The concept is easy enough -- you just ignore the water and non-VOC solvents, and pretend that you are dealing with an imaginary formulation that contains only the VOCs and the solids.  The number that you use is just the weight of VOCs per gallon of paint that the imaginary formulation would contain.  Adding water or other non-VOC liquids to the paint wouldn't change the imaginary formulation at all, so you can thin all you want, but the "VOCs per gallon of paint, less water" number will not change.

The tricky part is determining the number.  How do you go about measuring the number of pounds of VOC solvent in a gallon of fluid that never really exists?

Let's start with what the manufacturer of the paint already knows (and you know by looking at the label on the paint can).  When the paint is formulated, the manufacturer typically combines known weights of VOCs, non-VOC liquids, and paint solids into the paint blend, mixes well, and measures (or knows from production data) the volume of the final mixture.  Dividing the weight of each ingredient by the number of gallons of the final mixture provides the weight per gallon of that ingredient in the actual formulation.  What you need is the weight per gallon of the imaginary formulation. 

Even though the imaginary formulation never physically exists, you can create it by mathematical alchemy based on what you already know.  The trick is to start with the fraction that represents the weight of VOC solvents per gallon of the actual formulation (weight of VOC in the numerator, gallons of actual paint in the denominator).  You leave the numerator alone, but you subtract from the denominator the volume of non-VOC liquids in the actual formulation.  The new denominator is the volume of the imaginary formulation -- it's the number of gallons of paint you would have produced if you had never added the non-VOC liquids in the first place.  The new fraction (same numerator, smaller denominator) will be a bigger number than the old fraction.  And, most significantly for our purposes here, it won't change if you add more non-VOC liquids to the mix.  The new fraction is the "VOCs per gallon of paint, less water and non-VOC solvents" number that you use to determine compliance with the regulations, according to this method.

Note that even though the new number avoids giving false credit for simply thinning the paint, it still rewards the manufacturer for replacing some of the VOC solvent in a formulation with non-VOC compounds.  The reason is that if less VOC solvent is used in the first place, the numerator will be smaller.  So the "VOCs per gallon of paint, less water" method provides a reasonably good measure of environmental impact, with the right incentives built into it. 

One complication should be mentioned, however.  The alert reader will have noticed that you need to subtract the volume of non-VOC liquids in the denominator.  It is more typical (in industry, if not in American kitchens) to measure the weight of ingredients being added to formulation.  That in itself poses no big difficulty.  It isn't hard to convert the weight of a given liquid to a volume if you know the density of the liquid.  But we are making a hidden assumption that chemists will be aware of.  If you add a pound of A to a pound of B, you will always get two pounds of mixture.  But if you add a gallon of A to a gallon of B, you might or might not get two gallons of mixture.  If there is a strong molecular interaction between the two substances (as there is, for example, between water and sulfuric acid), the molecules in the mixture will "stack" differently from the molecules of the two separate substances, and the final blend can be considerably less than two gallons.

How do the regulations deal with this complication?  They ignore it.  You can assume, for purposes of this calculation that volumes are strictly additive.  But before you start comparing this procedure to the famous legislation that decreed that, henceforth, the ratio of the circumference of a circle to its diameter ("pi") would be exactly three and one-seventh, we should note, in fairness, that for most liquids used in coatings formulations, the error due to non-additivity of volumes will be small.

For VOCs, the formula used by the Emissions Calculator is:

VOCs emitted per gallon of coating, less water

On the right hand side of the formula, "wt of X per gal" always means to the weight of component X in a gallon of the final coating mixture.

If HAPs rather than VOCs are specified in the rule, the same formula is used, but with the weight and density of the non-HAP volatiles replacing the corresponding terms for water.

HAPs emitted per gallon of coating, less water align="center" class="body10" style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"> weight of HAP₁ per gallon + weight of HAP₂ per gallon + ...

VOCs or HAPs per gallon of solids

In the previous section, we saw that simply measuring the environmental impact of a paint by the weight of VOCs it contains per gallon can lead to undesirable regulatory incentives.  A paint could, for example, be thinned with a non-VOC solvent to bring it into compliance, but more of the thinned paint would be needed to apply the same coating thickness over a given surface area.  The same amount of VOCs would be released in either case, even though the thinned paint would be in compliance, and the original paint would not.  Achieving compliance just by adding a thinner, without reducing the actual environmental impact, seems contrary to the spirit of the regulations, so a different measure of environmental impact must be used.

The "VOCs per gallon of paint, less water (and "non-VOC" solvents)" method gets around the problem, but in an indirect way that is somewhat difficult to understand, and that has technical complications.  Since in many cases (see the next section for exceptions) the bottom line is really the volume (thickness times area) of solids deposited on the surface to be coated, why not use that quantity directly in the measure? 

That is exactly what the "VOCs per gallon of solids" method does.  You simply take the ratio of the weight of VOCs per gallon to the volume of paint solids in that gallon.  In that case, neither the numerator nor the denominator depends on non-VOCs, so the ratio does not change when thinners are added.

This method has the virtue of being easy to understand, and does not rely on an "imaginary formulation" that never really exists.  The difficulty with this approach lies in measuring the volume of paint solids.  When added to the paint formulation, the solids are generally in powder or granule form, and a pile of such materials will always contain some air spaces.  So you can't just measure the volume occupied by a pile of granules.  The pile will occupy a greater volume than a single chunk of the solid material would.

So how can you get a good measure of the volume occupied by the paint solids from the information that you do know?  The trick in this case is to use the known volume of the formulated paint mixture.  Instead of the space between the granules being occupied by an unknown volume of air, in the formulated paint the space is occupied by a known volume of paint solvents.  (Even if the liquid components of the paints were measured into the formulation by weight rather than by volume, it is easy to convert the weight of each liquid component into a volume by dividing by the density of the liquid.  And you can always determine the density of a liquid simply by measuring the volume occupied by a known weight of the liquid.  Unlike granular solids, there are no air spaces to complicate the measurement.)  You (or the paint manufacturer) know what volume of liquids you added, and you know what volume of paint you wound up with.  By subtracting the total paint volume from the liquid volume, you have calculated the volume of solids in the paint.

Now you have everything you need.  Take the total weight of the VOC liquids (ignoring the non-VOC liquids in the formulation) as the numerator, and the total volume of the solids that you just calculated as the denominator.  That fraction represents the weight of VOCs per gallon of solids, the quantity we're after.

What about the complication mentioned in the last section, about volumes not being additive?  That is theoretically a complication for this method also, but in practice it will typically matter even less in this case.  We have been using the word "solvent" somewhat loosely -- most paint solids are not dissolved in the liquids, but are simply suspended.  Solid particles and paint liquids are only in contact at the surface of the granules, so there is much less chance for molecular interactions to change the molecular "stacking patterns" in the materials.  In this case, the error will be so small that one would expect non-additivity of volumes to be a non-issue in virtually all cases.

Only the VOCs appear in the numerator, but all of the liquids, VOCs and non-VOCs alike (and water, if present) appear in the denominator.  On the right hand side, "wt of X per gal" always means the weight of component X in a gallon of the final coating mixture.

For HAPs, the formula is:

Again, only the HAPs appear in the numerator, but all of the liquids appear in the denominator.

VOC Calculator 3

VOCs or HAPs per weight of solids

Another way to handle the presence of non-VOCs is to calculate the ratio of the weight of the VOC solvents to the weight of the solids, rather than to the volume of the solids.  Again, neither the numerator nor the denominator depends on non-VOCs, so the ratio does not change when thinners are added.  One advantage is that the weight of the solids is easily determined.   Rather than being indirectly calculated, like the solids volume as in the last section, the weight can be measured directly.  Another advantage is that, in some cases, it really is the weight, rather than the thickness, of the deposited coating that matters.  An example would be coating over porous or absorbent surfaces, where the coating does not form a well-defined layer.

It might be argued that there is still a loophole in this method.  Paint manufacturers could presumably formulate a paint which is in compliance, but which does not improve the environmental impact of the paint.  Manufacturers could increase the weight of the solids (for example, by adding heavier metallic compounds that don't significantly affect the performance of the coating), and thereby bring the formulation into compliance without changing the VOC content.  Whether any manufacturer would actually try to take advantage of this type of loophole is speculation at this point.  It might be easier in practice simply to find non-VOC alternatives for the solvents (which is, after all, the point of the regulation), rather than to tinker with the solids.

On the right hand side, "wt of X per gal" always means the weight of component X in a gallon of the final coating mixture.

VOC Calculator 4

What solvents are considered "non-VOC" solvents?

One of the main reasons that air emissions of organic solvents are regulated is to protect human health.  If some solvents are less harmful than others, it makes sense for the regulations to encourage their use in preference to more harmful alternatives.

The most serious health effects caused by low concentrations of organic compounds in the air do not result directly from the compounds themselves, but from products of reactions that the compounds can undergo.  Three ingredients make for a particularly unhealthy stew:  VOCs, nitrogen oxides, and sunlight.  In the presence of ultraviolet light from the sun, VOCs and nitrogen oxides will react to produce ozone, a very reactive form of oxygen that attacks lung tissue.  Nitrogen oxides are produced by high temperature combustion (such as from vehicle engines and power plants), and are therefore present in most populated places.  Any additional VOCs will lead to more ozone, and thus more respiratory problems.

But some organic molecules are either already highly oxidized, or are very stable, and do not participate in these reactions.  Although they may be volatile and organic, they are excluded from the regulatory definition of "volatile organic compounds".  They are the "non-VOC" liquids referred to above.  They go by several other names as well.  The federal regulation that applies to this case refers to them as compounds "which have been determined to have negligible photochemical reactivity".  They are also called "exempt compounds", "VOC-exempt solvents", and other variations on those themes.

Examples of compounds that are considered non-VOC solvents include:

The fact that these are exempt from regulation as VOCs does not necessarily imply that they don't have other problems.  For example, the use of CFCs is now severely restricted (CFCs destroy ozone in the stratosphere, where we want it, even though they don't create ozone down here at ground level, where we don't want it), and several of the chlorinated hydrocarbons have other undesirable health effects.

To find a complete list of non-VOC solvents, the most authoritative source is the Code of Federal Regulations, since that will always be kept up to date.  The specific reference is Chapter 40, Section 51, Paragraph 100(s), or 40 CFR 51.100(s) for short.  To find out if a specific solvent is classified as VOC-exempt, you can find a number of sources for this type of information on the web.  An example is SOLV-DB^®.

List of coatings MACTs and corresponding measurements

The calculation method to be used for your particular situation is spelled out in the MACT rule that applies to you.  In some cases, MACT rules apply to specific industry sectors (such as Auto and Light Duty Truck, Metal Furniture and Wood Building Products.  But in other cases the rules apply to the nature of the materials being coated (such as Metal Coil, Miscellaneous Metal Parts, and Plastic Parts), and can affect a variety of different industry sectors.

Determining which rules apply to your specific situation can sometimes be an involved process.  EPA has provided specific guidance material for each rule that can help you make those determinations.  The table below is primarily intended to indicate which calculation methods are called out by which rules.  But it also includes links to web pages that EPA has prepared to help you find all of the guidance material available for each specific rule.  (This table includes surface coating MACTs only.  EPA also provides an alphabetical index to all of their MACT "Rule and Implementation Information" pages, not restricted to the surface coating MACTs.  Another reference source from EPA, covering a somewhat broader list of processes relevant to surface coating, can be found on their "" page.)

This table was last updated on 1/20/04.  To find information on the current status of these rules, click on the individual links in the first column below, or check the overview table on the PCRC website.

Clicking on a rule name in the first column of the table will take you to the EPA's MACT "Rule and Implementation Information" page for that rule.

Clicking on a citation in the "Reference" column will take you to a copy of the rule as published in the Federal Register.  The page number (last five digits) in the reference column is the page on which you can find an explicit reference to the measurement units used to express the emission limits established by the rule.  In some cases, the rule has not yet appeared in the Federal Register.  The reference is then to the latest copy of the rule available from EPA.

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