1 | Page

Scientific Critique of South Coast Air Quality Management District Paper

“Non‐Volatile, Semi‐Volatile, or Volatile:  

Redefining Volatile for Volatile Organic Compounds”

October 2012

ABSTRACT

A draft paper entitled “Non‐Volatile, Semi‐Volatile, or Volatile: Redefining Volatile for Volatile

Organic Compounds” authored by Uyên‐ Uyên T. Võ and Michael P. Morris is subjected to a

scientific critique.  The paper presents ambient evaporation data for organic compounds of

varying volatility that is portrayed as drawing into question the regulatory criteria and test

methods used to determine what low‐vapor‐pressure compounds are exempted from the

regulatory definition of “Volatile Organic Compound” (VOC) for various uses.  The paper fails to

grasp the crucial differences between the technical term “volatile” and the regulatory term

“VOC”, which relates to the ability to contribute significantly to formation of ozone in

tropospheric ambient air through vapor‐phase photochemistry.  In this critique, the scientific

concepts and studies are noted that limit the ability of low‐volatility organic compounds to

contribute significantly to tropospheric ozone formation and refute the arguments in the draft

paper.

SCIENTIFIC CRITIQUE

“Non‐Volatile, Semi‐Volatile, or Volatile: Redefining Volatile for Volatile Organic Compounds”

authored by Uyên‐ Uyên T. Võ and Michael P. Morris was obtained from the authors in the form

of a draft paper dated August 31, 2012, as well as a presentation dated June 21, 2012, that was

presented at an Air & Waste Management Association meeting.  This scientific critique was

conducted by a number of chemists and environmental scientists in the consumer products

industry.1

                                                           

1

  Scientists involved in developing this critique included representatives from the Consumer Specialty Products

Association, Personal Care Products Council, American Chemistry Council, American Cleaning Institute, American

Coatings Association, Automotive Specialty Products Alliance, National Aerosol Association, International Sanitary

Supply Association, and International Fragrance Association North America.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
2 | Page

The abstract of the paper begins with the erroneous statement that, “The term volatile organic

compound (VOC) is poorly defined because volatility is subjective.” (Page 1)  Volatility is not in

any way subjective, but rather is a basic, measurable physiochemical property that is well

defined.  It is measured as the pressure exerted by molecules of a substance’s vapor (i.e., gas

phase) in thermodynamic equilibrium with its condensed phase(s) (i.e., liquid and/or solid) in a

closed system at a given temperature.2

  Vapor pressure is often measured at 20°C or 25°C in

units of either mm Hg or pascals.3

  As vapor pressure increases with temperature, it is closely

related to boiling point, which is the temperature at which the vapor pressure is equal to the

pressure exerted by ambient air.  Numerous physical laws have been established relating to

vapor pressure and boiling point, including the Clausius‐Clapeyron relation of vapor pressure

with temperature, Raoult’s Law for calculating vapor pressures of mixtures, and many others.  

All liquids (and solids) have vapor pressures, but they are often too low to be measured

accurately.

As to the contention that the term “VOC” is “poorly defined,” this appears to be caused by the

apparent confusion between the technical scientific term and the regulatory term.  The

technical scientific term “VOC” is a relative term for which there are no set criteria for the

relative volatility needed for a material to be considered “volatile” under conditions of interest.   

However, the regulatory definition of VOC is quite different (and indeed much more restrictive)

than the scientific use of the term.   The current U.S. Environmental Protection Agency’s

regulatory definition of VOC for the purpose of regulatory enforcement of the Clean Air Act is

as follows:

"Volatile organic compounds (VOC)" means any compound of carbon, excluding carbon

monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium

carbonate, which participates in atmospheric photochemical reactions.4

Atmospheric photochemical reactions occur in the vapor phase in the troposphere.  

Consequently, the final phrase in this definition excludes compounds that are either too low in

photochemical reactivity (which EPA has defined as lower in ozone formation potential than

ethane) or too low in volatility (or having other physiochemical characteristics) to have

significant participation in atmospheric photochemistry.  EPA specifically evaluates and lists

individual chemicals having negligible photochemical reactivity as exemptions to the definition

                                                           

2

For example, Chang, Chemistry, 9th Ed., McGraw‐Hill, pg 518.  The U.S. EPA defines volatility as being indicated by

a substance's vapor pressure. It is a tendency of a substance to vaporize or the speed at which it vaporizes.

Substances with higher vapor pressure will vaporize more readily at a given temperature than substances with

lower vapor pressure. http://www.epa.gov/iaq/voc2.html#4 accessed 9/26/2012) 3 Conversion factors: 1 pascal = 0.0075 mm Hg; 1 mm Hg = 133.3 pascals.  High vapor pressures are often

expressed in kilopascals (kPa).  1 kPa = 1000 pascals. 4 40 CFR § 51.100(s)

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
3 | Page

of VOC.5  For low vapor pressure (LVP) compounds that do not participate due to low volatility,

EPA relies on a variety of test methods designed for specific commercial products or operations,

or in the case of consumer products, a definition of LVP based on the vapor pressure criterion

of less than 0.1 mm Hg at 20° C (which is equal to 13.3 pascals).

The authors are correct in noting that the various test methods currently used to measure the

amount of “VOC content” in a material differ markedly. (Page 1)  However, they do not make a

compelling case in their contention that, “These differences lead to varying VOC content results

which may conflict with one another, resulting in regulations that can limit the environmental

benefits anticipated or unnecessarily exclude potential alternative formulations.” (Page 1)

Indeed, contrary to the author’s apparent contention, all of the current methodologies used for

the determination of VOCs probably overestimate to varying degrees what materials in

commercial products and operations actually participate significantly in atmospheric

photochemistry.6

The authors are correct in noting that, “The EPA exempts solvents in consumer products with a

vapor pressure of 0.1 mm Hg or less at 20°C, concluding that those compounds have little or no

volatility and that an exemption will not result in significant VOC emissions and contribute to

ozone formation.” (Page 2) They are less correct in observing that, “However, the measurement

for vapor pressure becomes difficult at values below 7.5 mm Hg and most vapor pressure

endpoints are ten to a hundred times lower.” (Page 2)  While this has been historically true, the

vapor pressure methodologies incorporated by CARB into Method 3107 are fully capable of

accurate and precise measurements needed for assuring compliance with the 0.1 mm Hg

criterion.  In addition, the carbon‐number and boiling point criteria were not added by CARB in

the 1990s due to inaccuracy or imprecision of the vapor pressure measurements, but to simply

minimize (in the case of carbon‐number) needless testing of known nonvolatile materials, and

(in the case of boiling point) to easily accommodate complex hydrocarbon mixtures that may

contain both LVP and more volatile constituents.  In addition, the criterion is not “12 or more

carbons” but rather “more than 12 carbons.” (Page 3)8

The European and Canadian 250°C boiling point criterion (Page 3)  is only found in their current

paint regulations, and is not relevant to other consumer products, which have yet to be

                                                           

5 Ibid, 51.100(s)(1) 6 For example, Mania, Daniel J., Bruck, Michele L, Fezzey, Sarah, Floyd, F. Louis —PRA Laboratories, Inc., "Sources

of Error in VOC Determination via EPA Method 24", Journal of Coatings Technology, 73, (919), August 2001,

http://www.eaglabs.com/cmss_files/attachmentlibrary/Source‐of‐Error‐in‐VOC‐Determination‐via‐EPA‐Method‐

24.pdf, accessed 10/1/2012. 7 Method 310 incorporates an improved version of ASTM D 2879‐97 (Isoteniscope) and ASTM E 1719‐97

(ebulliometry).

8 40 CFR § 59.203(f)(2) and 17 CCR § 94508(98)(B)

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
4 | Page

regulated in those jurisdictions; when Canada does adopt a consumer product VOC regulation,

they are currently planning consistency with USA regulations by CARB, OTC and EPA. The

authors are also not accurate about consumer products in stating that, “Green Seal exempts

solvents with a boiling point of 280°C.” (Page 3)  That criterion is also only relevant to the Paints

and Coatings standard; in all of the Green Seal consumer product standards, they use the same

LVP criteria as CARB (and all other consumer product regulations) and rely on Method 310.9

   

Much of the information and vapor pressure data on compounds in the “Evaporation Rate”

study shown in Table 1 (Page 4) appears generally accurate, and largely consistent with results

obtained in many laboratories for most of these materials, but it is important to note that those

reported as “<0.01” to “<0.001” are probably not quantitatively reliable.  (It is important to

note that the vapor pressures provided are expressed in mm Hg at 25°C instead of 20°C, which

makes comparison to values measured via Method 310 difficult.)  In addition, the MIR

(maximum incremental reactivity) data for the low volatility species cannot be considered

reliable.  Dr. William Carter included estimates for many of these materials in his lists of MIR

values despite an inability for these materials to remain in the vapor phase long enough to

participate in chamber photochemistry where reactivity is measured and photochemical

mechanisms determined.10  With materials like alkyl alkanolamine, methyl palmitate, soy oil,

and glycerol, Dr. Carter clearly indicates in footnotes that these data are highly uncertain.11  It is

indeed likely that some of these materials exhibiting vapor phase photochemistry were the

result of thermal degradation from the high temperatures at which they had to be injected into

the chamber.12

This problem of thermal degradation may indeed be a problem with most if not all of the

current test methods used to determine VOC content in various non‐consumer products.  (Even

Method 310 begins with a high‐temperature—100°C—gravimetric determination of total

volatiles that will quite often result in thermal degradation of some ingredients, and therefore

give inaccurate determination of total volatiles; Method 310, however, includes sufficient other

methodology to allow CARB’s laboratory to correct this error.)  

                                                           

9 See various Green Seal standards for consumer products at

http://www.greenseal.org/GreenBusiness/Standards.aspx?vid=StandardCategory&cid=3.   10 Carter, William P. L. Development of the SAPRC‐07 Chemical Mechanism and Updated Ozone Reactivity Scales,

Report to the California Air Resources Board, Contracts No. 03‐318, 06‐408, and 07‐730, Revised January 27, 2010,

http://www.cert.ucr.edu/~carter/SAPRC/saprc07.pdf, accessed 9/28/2012. 11Updated Maximum Incremental Reactivity Scale And Hydrocarbon Bin Reactivities For Regulatory Applications,

Prepared for California Air Resources Board Contract 07‐339 by William P. L. Carter, College of Engineering Center

for Environmental Research and Technology, University of California, Riverside, CA 92521, Revised January 28,

2010. 12Carter, William P. L. , Luo, Dongmin, Malkina, Irina L., Investigation Of Atmospheric Ozone Formation Potentials

Of C12‐C16 n‐Alkanes, Report to The Aluminum Association, Contract AA1345, October 28, 1996,

http://www.cert.ucr.edu/~carter/pubs/alkrept.pdf, access 9/27/2012

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
5 | Page

A more thorough analysis of the results shown in Table 1 (Page 4) reveals that the work actually

support the LVP exemption for consumer products.  The ambient evaporation results labeled as

“Time to 100% evaporation” in Table 1 correlate very well with their reported vapor pressures

at 25°C with the single exception being C9‐C16 Hydrotreated Light Distillate.13

The evaporation results also can be shown to properly predict the regulatory classification (LVP

versus VOC) when a cutoff value of ten days (rather than the 180 days reflected by the authors)

is used in the column labeled “Time to 100% evaporation” as shown in Table 1.  Three of the

four compounds with “Time to 100% evaporation” values less than ten days are classified as

VOCs; the single exception is Light Distillate which is classified as LVP.14  The other 17

compounds with “Time to 100% evaporation” values greater than ten days are classified as

LVPs.   

Thus, these results show that compounds that evaporate fast are VOCs and compounds that

evaporate slowly (if at all) are LVPs; VOCs therefore indeed can be classified by their vapor

pressure.  Correspondingly an LVP that is unlikely to enter the vapor phase will have a lower

potential for ozone formation (discussed in more detail below).  All this is consistent with the

current LVP exemption for consumer products.     

The “Overall Ambient Evaporation Results” in Figure 1 (Page 6) also appear generally accurate,

and largely consistent with results obtained in many laboratories for most of these materials.  

However, the assignments of “Volatile,” “Semi‐Volatile” and “Non‐Volatile” are purely

subjective, and not directly relevant to determination of which materials should be classified as

VOCs by the regulatory definition.  More specifically, the ability for a compound to temporarily

enter the vapor phase does not demonstrate the ability to persist in the vapor phase

sufficiently to make it available to significantly contribute to ambient atmospheric

                                                           

13 The chemical identity of light distillate referred to by the authors and corresponding data appears to be in

question.  The C9‐C16 carbon number range appears to come from the description of CAS# 64742‐47‐8 which also

includes a boiling range of 150‐290°C, while the authors cite a boiling range of 216‐278°C. It does not appear to

match any ASTM D86 boiling ranges for products on the Calumet website. Additionally a C9‐C16 carbon number

designation is inconsistent with a boiling range of 216‐278°C. Using the boiling points of normal paraffins to define

carbon number bins, as is customary for hydrocarbons, the carbon number range for 216‐278°C should be C13‐

C16. Boiling points above 216°C indicate that this particular material should be LVP‐VOC. It is possible to have

VOCs and LVP‐VOCs within the CAS# 64742‐47‐8 definition of light distillate, and determinations of VOC or LVP‐

VOC should be by the actual boiling range of each product, which is why the US EPA provides a range of vapor

pressures for light distillates.  CAS# 64742‐47‐8 is associated with three separate ingredients used in consumer

products in the CSPA Consumer Product Ingredients Dictionary (First Update, Second Edition, October 2012), and is

therefore not useful in specifying a specific hydrocarbon mixture. 14 USEPA reports Light distillate vapor pressure ranges from 0.03 to 5.4 mm Hg at 25°C, so it may be a LVP

depending on the particular mixture tested.  SCREENING‐LEVEL HAZARD CHARACTERIZATION

Kerosene/Jet Fuel Category, March 2011, pg. 9, http://www.epa.gov/chemrtk/hpvis/hazchar/Category_Kerosene‐

Jet%20Fuel_March_2011.pdf.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
6 | Page

photochemistry, nor is it indicative that a compound has a predominately atmospheric

environmental fate.15

The authors consider only pure solvents evaporating from open dishes or other methods

designed to aggressively evaporate solvents; that may not represent actual product formulation

and use which have very different conditions.  In most cases these solvents are combined with

other ingredients, such as surfactants, polymers and other lower vapor pressure analogues that

inhibit evaporation or the solvent may also react with other ingredients and remain locked in

the product.  During product use, the ingredients may be contained in such a way that

opportunities for evaporation are reduced or eliminated.  There may be retention of the spent

material in an applicator that is subsequently discarded and removed to a landfill or rinsed

down a drain.  Emissions from landfills and sewage treatment facilities are independently

calculated and these materials may be completely retained or degraded.  During use and

disposal these types of consumer products are not usually discharged directly into the air,

therefore a fugacity model must be used to demonstrate what component of the solvent might

escape to air when discharged to another medium.  Even for consumer products whose use

results in emission to air, fugacity modeling is needed to determine whether the LVP or VOC

compound remains in the air in the vapor phase and has the potential to engage in atmospheric

photochemistry, or partitions out into other environmental media where it will be biodegraded.

The following table shows the results of subjecting some of the compounds and materials from

“Overall Ambient Evaporation Results” in Figure 1 (Page 6) to evaluation using a Level III multi‐

media fugacity model (LEV3EPI) within the U.S. EPA EPI Suite v4.1.16  The environmental

distribution predicted in this model show that the materials considered LVPs in consumer

product regulations often have environmental fates predominantly in water and soil rather

than air, and therefore have limited availability to participate in atmospheric photochemistry

and thereby fail to significantly promote tropospheric ozone formation.  These data clearly

show that most LVPs, and many VOCs as well, do not contribute significantly to ambient air

photochemistry or formation of tropospheric ozone.

                                                           

15Final Proceedings Workshop on Combining Environmental Fate and Air Quality Modeling Organized by the

Reactivity Research Working Group's Atmospheric Availability and Environmental Fate Subgroup, June 27‐29, 2000,

Research Triangle Park, NC, http://narsto.org/sites/narsto‐dev.ornl.gov/files/Appendix_F_Vol%26Fate.pdf,

Accessed 9/25/2012   16 http://www.epa.gov/oppt/exposure/pubs/episuite.htm, accessed 9/26/2012

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
7 | Page

Table 1: Võ and Morris (2012) selected organic compounds sorted by “Time to 100% Evaporation” with added environmental

distribution results from the LEV3EPITM model.  *Non‐volatile (NV), semi‐volatile (SV), and volatile (V)17

Compound name Classification

based on

Evaporation

at 6 months*

Regulatory

Classification

in Consumer

Product

Regulations

Time to

100%

Evaporation

(days)

Vapor

Pressure

(mm Hg

@ 25

C)

Predicted Partitioning

Air (%) Water

(%)

Soil (%) Sediment

(%)

Isopropyl Alcohol

(IPA)

V VOC 0.9 33 4.58 45.2 50.1 0.0856

Ethyl Lactate V VOC 1.9 1.2 3.61 43.7 52.6 0.0818

C9‐C16

Hydrotreated

Light Distillate

(Light Distillate)

V Partial VOC/

Partial LVP  

1.9 <0.01 to

0.3

22.4 69 2.51 6.15

N‐Methyl

pyrrolidinone

(NMP)

V VOC 9.2 0.5 0.066 32.5 67.3 0.0697

Benzyl Alcohol V LVP   14 0.14 1.03 34 64.8 0.0929

Dodecane (C12) V VOC 16 0.3 22.4 69 2.51 6.15

Propylene Glycol V LVP 63 0.13 0.397 34.5 65 0.061

Ethylene Glycol V LVP 126 0.09 1.44 36.1 62.4 0.0638

2,2,4‐

Trimethylpentane

diol Diisobutyrate

V LVP 147 0.004 0.85 18.6 80 0.503

2,2,4‐Trimethyl‐

1,3‐Pentanediol

Isobutyrate

V   LVP 154 0.01 0.883 29.6 69.4 0.0906

Pentadecane

(C15)

SV LVP >180 0.01 11.1 72.4 5.61 10.9

Dipropylene

Glycol

SV LVP >180 <0.01 0.0771 38.4 61.5 0.0718

2‐Methyl

Hexadecane

SV LVP >180 <0.01 7.46 80.2 3.5 8.82

Hexadecane (C16) SV LVP >180 0.005 3.46 37.5 55 4.08

Naphthenic Oil

(Hynap N60HT)

SV LVP >180 <0.001 unknown unknown unknown   unknown

Heptadecane

(C17)

SV LVP >180 <0.001 10.4 78.4 5.72 5.44

Naphthenic Based

Metal Working

Fluid (MWF)

SV LVP >180 unknown unknown unknown unknown   unknown

Alkyl

Alkanolamine

NV LVP >180 <0.01

0.000728 37.8 62.2

0.071

Methyl Palmitate NV LVP >180 <0.001 1.96 20.5 73.5 3.97

Soy Oil NV LVP >180 <0.001 0.0103 17.8 82.2 4.97E‐09

Glycerol NV LVP >180 <0.001 0.484 35.3 64.2 0.0624

                                                           

17 The modeling study that provided the above partitioning data examined the environmental distribution of the

selected VOCs using a Level III multi‐media media fugacity model (LEV3EPITM) within the USEPA EPI SuiteTM (2012)

software package which is based on the work of Mackay et al (1996).   The model predicts the partitioning of

compounds among air, soil, water, and sediment under steady state conditions for a default model environment.  

The model default input values were used in this analysis; environmental emission rates were 1000 kg/hr to air,

1000 kg/hr to water, 1000 kg/hr to soil, and zero emissions to sediment.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
8 | Page

These data, shown in Table 1 above, clearly support the minimal potential atmospheric impact

for many lower volatility compounds, particularly those compounds with high water solubility.  

Even more volatile (but polar and highly water soluble) compounds such as isopropanol and

ethyl lactate (both VOCs) have only a limited percent of their emissions remain in the air, with

the balance partitioned out into water and soil, where it is readily biodegraded.  Even the non‐

polar hydrocarbon LVPs18 are partially partitioned into other environmental compartments

rather than remaining in the ambient air.  The media into which discharge occurs can have a

significant impact on the partitioning.  Therefore, for product uses that result in emissions

solely to other media (e.g., water or soil), even lower air fates can be expected for these

compounds.  

The modeling study data above predicts that only limited percent of the LVP masses stay

partitioned in the air, as shown in Table 1, not the 100% of the mass implied by the authors.  

LVPs prefer to partition into the water or soil environmental compartments.  Other multi‐media

modeling studies, such as the study by Foster, et al (2006) have also reported that the less

volatile chemicals partition into the soil and water, thus a lower fraction of the emitted mass

reacts in the atmosphere and a significantly lower fraction of the emitted mass is a potential

ozone precursor.19   The study by Foster clearly showed that at volatilities below 10 Pa (0.075

mm Hg), hydrocarbons begin to partition from air in the urban environment to water, soil,

vegetation and urban film.20  The important role of urban films in the sorption and removal of

organics from the air has been recognized more fully in recent years.21

The important question is “does the exemption of LVP solvents reduce ozone formation.”  A

careful scientific evaluation shows the answer to be yes: lowering volatility can be as important

as lowering reactivity in lowering VOC emissions and ozone impacts.  Several steps are required

to form ozone via atmospheric photochemical reactions.  The first step is that a consumer

product has to be used in a manner that results in a vapor phase emission, and the second step

is that the VOC has to remain in the vapor phase long enough to reach the ambient

atmosphere, and then remain available in the vapor phase long enough to become engaged in

tropospheric photochemistry.  LVPs have more time to biodegrade or to distribute into other

                                                           

18 The most non‐polar compounds are C9‐C16 Hydrotreated Light Distillate (Light Distillate), Dodecane (C12),

Pentadecane (C15), 2‐Methyl Hexadecane, Hexadecane (C16), Naphthenic Oil (Hynap N60HT), Heptadecane (C17),

Naphthenic Based Metal Working Fluid (MWF), Methyl Palmitate and Soy Oil. 19 The Role of Multimedia Mass Balance Models for Assessing the Effects of Volatile Organic Compound Emissions

on Urban Air Quality”, Karen L. Foster, et al, Atmospheric Environment 40 (2006) 2986‐2994. 20 Ibid. 21 “Modeling Urban Films Using a Dynamic Multimedia Fugacity Model,” Chemosphere 87 (2012) 1024‐1031.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
9 | Page

environmental compartments, such as water or soil, rather than distribute into the air and help

form ozone.

The authors could have performed a more relevant study, such as measuring concentration of

these VOCs in the air over time.  As noted by Carter in his MIR studies, many organic materials

are “sticky”22 and this is an indication of how likely both VOC and LVP are to become

incorporated in surface films and biological materials.23  The evaporation studies would have

been much more realistic had they included typical formulations and typical surfaces in the

chamber, and then evaluated ambient concentrations of organic materials in air samples taken

periodically.  This would have been a more appropriate means for determining the potential

vapor emissions of organic compounds in consumer products, especially in formulations in

conditions consistent with typical usage.

Many of the materials that the authors classify as “Volatile Compounds” (Page 6) because they

can evaporate within six months actually would not be expected to contribute significantly to

ambient air VOCs.  Even isopropanol and ethyl lactate, the most volatile compounds evaluated

(and both VOCs), only have limited air fates, with the balance being biodegraded in water and

soil.  Propylene glycol and ethylene glycol, classified as LVPs, demonstrate only very limited air

fate, again with most being biodegraded in soil and water.  The two isobutryates, both LVPs by

vapor pressure, also contribute little to air, and both have extremely low MIRs, near that of

ethane and acetone, considered negligibly photochemically reactive.  Benzyl alcohol, an LVP,

also contributes minimally to air emissions.

The authors correctly note that some of the materials tested are “Non‐Volatile Compounds,”

(Page 8) but the category of materials that the authors label as “Semi‐Volatile Compounds” due

to their ability to evaporate as little as 5% over six months (Page 9) is overly broad.  Dipropylene

glycol was included by the authors, a material that can be expected to contribute only minimal

emissions to the air (see data above).  Even the C15, C16, and C17 hydrocarbons partially

partition into soil and water, and also exhibit extremely low MIRs (0.50, 0.45 and 0.42),

approaching that of ethane (0.26) and acetone (0.35), both exempted from the regulatory

definition of VOC as negligibly photochemically reactive.  If the MIRs for consumer product LVPs

were attenuated by fugacity modeling, many LVPs could be shown to have ozone impacts

smaller than ethane.  (Indeed, many VOCs used in consumer products likewise would be

demonstrated as negligible in their ozone impact.)  In short, the exemption of LVPs in consumer

                                                           

22 Carter, William P. L. , Luo, Dongmin, Malkina, Irina L., Investigation Of Atmospheric Ozone Formation Potentials

Of C12‐C16 n‐Alkanes, Report to The Aluminum Association, Contract AA1345, October 28, 1996,

http://www.cert.ucr.edu/~carter/pubs/alkrept.pdf, access 9/27/2012 23 For example, Corsi, Richard L., Won, Doyun, Rynes, Mike, "Sorptive Interactions between VOCs and Indoor

Materials", Indoor Air, 11, 2001, 246–256.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
10 | Page

products is consistent with the intent of the U.S. EPA in exempting compounds as negligibly

photochemically reactive.

The results shown above are obtained from modeling wherein the materials are emitted into

the ambient environment.  If the environmental emission is solely in water or soil, with no

direct air emission, the percentage of a material staying in those other environmental

compartments is greatly increased.  In addition, for indoor air emissions, a significant

percentage of the emission of various materials might not reach ambient air due to sorption

and degradation indoors.24

The studies of evaporation reported by Morris and Võ fail to account for the mass balance of

materials.  As noted in the fugacity models above, there are many potential fates for organic

materials.  Unless that fate is availability in the vapor phase for atmospheric ozone reaction, the

materials should not be counted as VOCs by regulatory definition.  At minimum, the

evaporation studies should have been conducted in a closed space with sampling capability.  

Representative samples of air could then have been analyzed to demonstrate that the materials

could have reacted with NOx.  The difficulty reported by Dr. Carter, the principle atmospheric

reactivity researcher used by both SCAQMD and CARB, in volatilizing these “sticky” compounds

suggests that the materials are not likely to be available for atmospheric reactions.25

In comparing the use of various test methods to determine “VOC Content” of various materials,

the authors correctly conclude that differences exist. (Pages 9‐11)  It is clear that these

methodologies were designed for differing purposes.  One commonality that should be noted in

the three standard methods (GC, TGA and M24) is the use of high temperatures.  Few if any

consumer products are subjected to high temperatures during normal use, and tests using high

temperatures might not correctly simulate actual air emissions at ambient temperatures.  Many

materials degrade or otherwise react at high temperatures in ways not seen at the ambient

temperatures at which the products are designed to be used.  This effort to redefine LVP‐VOC

does not acknowledge the possibility of thermal degradation for the tested materials.

                                                           

24For example, see Springs, M., J. R. Wells, Morrison, G. C.. 2011. “Reaction Rates Of Ozone And Terpenes

Adsorbed To Model Indoor Surfaces.” Indoor Air 21 (4) (August 1): 319‐327. Weschler, Charles J., Nazaroff, William

W.. 2008. “Semivolatile Organic Compounds in Indoor Environments.” Atmospheric Environment 42 (40)

(December 1): 9018‐9040. Won, D, Rynes, M.. 2008. “Sorptive Interactions Between VOCs And Indoor Materials.”

Indoor Air (January 1). Jia, C., S. Batterman, C. Godwin, S. Charles, Chin, J‐Y. 2010. “Sources and Migration Of

Volatile Organic Compounds In Mixed‐Use Buildings.” Indoor Air 20 (5) (October 1): 357‐369. Weschler, Charles J.,

Nazaroff, William W. 2010. “SVOC Partitioning Between The Gas Phase And Settled Dust Indoors.” Atmospheric

Environment 44 (30) (September 1): 3609‐3620. 25 Carter, William P. L. , Luo, Dongmin, Malkina, Irina L., Investigation Of Atmospheric Ozone Formation Potentials

Of C12‐C16 n‐Alkanes, Report to The Aluminum Association, Contract AA1345, October 28, 1996,

http://www.cert.ucr.edu/~carter/pubs/alkrept.pdf, access 9/27/2012

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
11 | Page

The authors’ evaluation of boiling point versus “% Non‐Volatile” (as found in their evaporation

study) in Figure 8 (Page 12) clearly demonstrates the unreliability of their study in predicting air

emissions and ozone impacts.  Boiling point correlates well with vapor pressure, since they are

essentially the same attribute simply measured at different temperatures.  But even boiling

point and vapor pressure do not represent a straight‐line correlation.  It is important to

understand that the use of the alternative boiling point criterion in the consumer products

regulations is based on normal hydrocarbons, which have the highest boiling point for a given

vapor pressure of the materials at 20°C.  Polar organics of a given vapor pressure tend to have

lower boiling points.  The same is true of the carbon‐number criteria, which correlates only very

roughly with volatility when materials of very different chemistries are included.26  Normal

hydrocarbons have the highest carbon‐number (C12) that can demonstrate vapor pressure

above 0.1 mm Hg at 20°C.  Therefore the alternative carbon‐number and boiling point criteria

for LVPs simply serve to avoid unnecessary vapor pressure determinations and can be

permitted only when the vapor pressure is unknown or known to have correlation with a

known vapor pressure.

The data in Figure 10 (Page 14), presented as “Correlation of Vapor Pressure and Ambient

Evaporation Rates” does not show a correlation between “% Non‐Volatile” and “Vapor

Pressure” as the authors indicate, again demonstrating the unreliability of the authors’ “% Non‐

Volatile” criterion.  (Figure 8 shows that every material had either zero “% Non‐Volatile

Content” and/or zero vapor pressure.)  Vapor pressure is a basic physiochemical property of

every organic compound, and correlates significantly with atmospheric availability.   “% Non‐

Volatile” as defined by the authors appears to have no such correlation.

Despite the author’s errors previously mentioned regarding the Green Seal, EU and Canadian

VOC/LVP criteria, the summary in Table 4 (Page 16), in conjunction with the information already

noted above, provide clear evidence that the three test methods evaluated may be significantly

overestimating the VOC emissions and ozone impacts for the materials and operations with

which they are used.

The conclusions cited by the authors (Pages 17‐18) represent a failure to understand the basic

physical and chemical concepts that currently provide a scientific understanding of volatility,

environmental fate, and atmospheric availability that can be used to determine what materials

and uses can result in significant contributions to tropospheric ozone formation.  A careful

review and analysis of all data would show that lowering volatility is a valuable tool in lowering

ozone formation, both in terms of lowering air emissions (lower volatility materials generally

result in lower amounts of materials lost to evaporation during use), and lowering atmospheric

                                                           

26 Both boiling points and carbon‐number usually correlate well with volatility, however, within most closely‐

related groups of chemicals, e.g., linear alkanes, linear alcohols, etc.

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2
12 | Page

availability and increasing alternative environmental fates.  A major recommendation would be

for the authors to have allowed an external peer review to ensure the scientific validity,

completeness of contemporary review and improve the overall quality of the paper.

SUMMARY AND CONCLUSIONS

Our scientific critique of this SCAQMD paper on volatility has identified numerous flaws and a

basic misunderstanding of the environmental science and the atmospheric photochemistry, as

well as the regulatory definition of VOC.  Our critique uses publicly available and generally

accepted scientific models to demonstrate that consumer product LVPs (and indeed many

consumer product VOCs) do not participate significantly in atmospheric photochemistry or

tropospheric ozone formation.

Regulatory policies cannot be changed by a single study that provides no practical alternatives.  

The six‐month evaporation study is not a practical alternative to current regulatory criteria, nor

is it relevant to the goal of reducing the impact of VOC emissions or their impacts on

tropospheric ozone formation.

While the science is complex, and regulations need to be readily understandable to be

workable, the consumer products regulatory approach of lowering volatility through an LVP

exemption using a vapor pressure criterion is a valid and effective approach, and very

comparable to the way relative photochemical reactivity is generally considered through

exempting organic compounds with lower reactivity (i.e., lower ozone impact) than ethane.

###

Attachment D - CSPA Comments on ARB Agenda Item # 13-2-2