Printech Archive, February, 2000
Re: VOC content/photochemical reactivity

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Date: Fri Feb 25 2000 - 13:34:09 CST


I agree with your opinion that VOCs and VOC content determination is one
the more simpler, but confusing aspects of environmental regulation. The
you look into it, the more complicated it becomes. As Dave Salman point
in his response to your email, unless a chemical is placed on the list
exempt compounds, it is considered a VOC. In order to get on the list of
exempt compounds, a formal petition needs to be prepared and submitted
EPA. The petition needs to include the scientific data supporting the
for negligible photochemical reactivity.

In terms of determining VOC content, Method 24 is principal method for
materials, principally inks and coatings. Method 24 allows for the
subtraction of water and exempt compounds from the final VOC content

While the above seems straight forward, the confusion begins in the
determination of the photochemical reactivity of any given chemical. EPA
not published a formal protocol on this extremely essential subject.
appears to be current policy is that the reactivity of the chemical in
question needs to be compared to that of ethane. Those chemicals whose
reactivity is greater than ethane are VOCs and those, whose reactivity
less, can be placed on the exempt list.

Specifically, the reactivity is measured by how much ozone is produced
either a molar or gram basis. The gram basis looks at the weight of
produced per weight of test compound compared. The other measure is
which is best thought as a concentration and not weight. EPA has changed
position several times over the years on the on significance of the mole
gram basis and it appears to be shifting back to the mole basis.

As background, acetone was added to the list of exempt compounds based
on the
gram approach to measuring reactivity. When EPA delisted acetone and
who follow this issue realized the significance of the shift in policy
from a
molar to a weight basis, EPA was flooded with petitions, including the
petition submitted by the printing industry to delist ink oil. After the
acetone decision, EPA began to examine its revised policy and has
that a weight basis is far more difficult to defend and is not

In discussions with EPA on how photochemical reactivity is defined,
should be viewed as an anomaly. While it seems to be certain that ethane
be used as the benchmark for comparison, the measure of reactivity has
through some changes. Since the vast majority of chemical reactions are
examined on a molar basis, mole comparisons are more scientifically
acceptable. It is interesting to note that on a molar basis acetone
more ozone than ethane.

Therefore, in the methyl acetate decision, EPA stated that only those
compounds that produce less ozone than ethane on a molar basis would be
considered for delisting. The good aspect for methyl acetate is that is
reactive than ethane on both a molar and gram basis. EPA's position in
proposal to delist t-butyl acetate also further strengthens the molar
approach. However, EPA did solicit comment on how reactivity should be

The standard approach to measuring photochemical reactivity is to use a
chamber, which simulates what would happen to the test compound as it is
released into the air. There are two active smog chambers in the US, one
California and the other in North Carolina. Each smog chamber uses a
different approach to generate data. One uses a simpler urban air mix as
matrix and UV lights, while the other uses a more complex urban air mix
sunlight to drive the photochemical reactions. EPA generally likes to
data from both chambers in evaluating the reactivity of a chemical.

Computer models complimented with actual research data have not evolved
to a
point where a structure activity relationship can be easily predicted.
is some research being conducted in this area, but it is not sufficient
have definitive conclusion for the very near future. Some of the
research has
also indicated that the reactivity of any given compound is greatly
influenced by the "environment" in which it is emitted. Several studies
shown that the reactivity of ethane, which was once thought of being
actually varies.

It is also interesting to note that some of the older literature on
photochemical reactivity indicates that hexane along with other
chemicals is
not photochemically reactive. This conclusion was based on some early
performed in the 1960's and 1970's. The concept of just regulating
photochemically reactive chemicals was first incorporated into
regulation via
Rule 66, which was implemented in Los Angles. Other states quickly
suit and you still have today regulations on the books in certain states
limit the emissions of photochemically reactive chemicals as well as
These regulations, of course, add confusion to the entire topic of
air pollution emissions.

The last point to be made in this overall discussion is the role of
24. Method 24 has served as the backbone of VOC content determination
the early 1980's. However, it does have some limitations and has been
modified since its original release. The modifications have not kept
with evolutions in materials. More reactive cured (e.g., UV and EB) and
water-based materials are used today than in the 1980's and this has
demands on Method 24. While Method 24 has been modified, it needs to be
further modified. One good modification that occurred was to address VOC
content determination of reactive cured materials. The problem is that
modification only accommodates "thick film" inks, paints, and coatings.
method still can't be used for thin film materials, such as UV inks and
coatings used by printers. An ASTM subcommittee is currently working on
modification, but until one is designed, approved, and adopted, it could
years. In the interim EPA is working on some guidance.

The other major problem with Method 24 is that it can't tolerate
with high levels of water. While there are some precision adjustments
permitted, its precisions and reproducibility with water-based materials
leaves a lot to be desired. EPA has been working on this problem for
years, but has yet to find an appropriate solution. EPA does have some
existing guidance on precision adjustments.

To a lesser extend, there have been problems reported with precision and
reproducibility with solvent-based materials, which were the materials
the method was designed to measure. It seems that if the same sample is
to different labs, you can get different results. I only have a limited
amount of data on this topic and a thorough evaluation of this problem
graphic arts materials needs to be performed.

I hope that the above answer has shed some light on your question. If
have any more questions, let me know.

Gary Jones
Graphic Arts Technical Foundation
200 Deer Run Road
Sewickley, PA 15143
412/741-6860 x608 - Phone
412/741-2311 - Fax

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