Pressure Points
MIR: What is it and
why should you care?
10 Spray July 2019
NICHOLAS GEORGES
HCPA Senior Director
Scientific & International Affairs
ngeorges@thehcpa.org
For all you space aficionados—no, I’m not discussing Mir, the
first modular space station. Sorry.
As readers of SPRAY, you are no doubt aware that the
California Air Resources Board (CARB) has initiated a new
rulemaking to achieve further reductions in volatile organic compound
(VOC) content from consumer products. These reductions
are necessary to meet California’s current State Implementation
Plan (SIP).
Why does CARB (and the U.S. Environmental Protection
Agency EPA, along with other states) regulate VOC content from
consumer products? You have no doubt heard about ozone—a gas
that is composed of three atoms of oxygen (O3). In the Earth’s
upper atmosphere, called the stratosphere, ozone forms a protective
layer that shields us from the sun’s harmful ultraviolet rays.
However, at ground-level (the troposphere), ozone is a harmful air
pollutant and can trigger a variety of health problems.
When certain VOCs react with oxides of nitrogen (NOx) in the
presence of sunlight and heat, ground-level ozone is formed. Not all
VOCs react with nitrogen oxides to form ozone; and various VOCs
don’t yield the same amount of ozone. The Maximum Incremental
Reactivity (MIR) value of a chemical informs us how much ground
level ozone can potentially be formed, provided that the other components
needed in the reaction to form ozone are present.
For their current rulemaking, CARB aims to reduce statewide
VOC levels between 2–4 tons per day (tpd) by 2023 and to 8–10
tpd by 2031. We fully support CARB’s efforts to improve air
quality and clearly recognize that we need to contribute our fair
share to help achieve this goal. However, the consumer and commercial
products industry also needs to manufacture products that
are effective and improve the daily lives of those that use them.
In many product categories, VOC limits have been decreased
to the point where additional lowering would negatively impact
the performance and efficacy of these integral products. After 30
years of regulating the VOC content of consumer and commercial
products, there are not many areas left for CARB to obtain the
reductions they are pursuing.
MIR is a potential solution. Reactivity-based limits could
provide more formulation flexibility while efficiently reducing the
ozone formed from these products.
You may wonder why we currently regulate consumer and
commercial products by VOC content when there appears to be
a better, more direct solution to lowering the amount of groundlevel
ozone. That answer is probably best summarized by a 1995
EPA report to Congress1 (emphasis added):
To be most effective, ozone control strategies ideally should be based
not only on mass VOC and NOx emissions but should consider the
relative photochemical reactivity of individual species, the VOC-to-NOx
ratios prevalent in specific airsheds, and other factors which could work
together to minimize the formation of ozone with minimum adverse
impacts. Reactivity data on VOC, especially those compounds used
to formulate consumer and commercial products, is extremely limited.
Better data, which can be obtained only at a great expense, is
needed if EPA is to consider relative photochemical reactivity in any
VOC control strategy. In the meantime, a practical approach is to act
on the basis of mass VOC emissions.
Before the EPA sent its report to Congress, the work was well
underway to measure the differences in reactivities of VOCs and
the potential amount of ground-level ozone. CARB and industry,
which included members of the aerosol industry, had recognized
this need. This led them to fund Dr. William (Bill) Carter’s environmental
chamber studies of the MIR of VOCs at the Statewide
Air Pollution Research Center (SAPRC) at the University of
California at Riverside. The experiments consisted of repeated
6-hour indoor chamber irradiations of a simplified mixture of
ozone precursors with NOx in excess, alternating tests of varying
amounts of an added VOC.
The results of Dr. Carter’s experiments paved the way for the
Regulation for Reducing the Ozone Formed from Aerosol Coating
Product Emissions2 to regulate products based on reactivity,
not mass-based VOC content and served as a model for EPA’s
National Volatile Organic Compound Emission Standards for
Aerosol Coatings.3
MIR-based limits are continuing to gain traction, and last summer,
CARB amended its Regulation for Reducing Emissions from
Consumer Products4 with an alternate compliance option for
multi-purpose lubricants5 based on reactivity. The alternate option
was added after industry demonstrated that meeting the 10%
VOC content limit for multi-purpose lubricants was not commercially
and technologically feasible.
CARB staff conducted technical assessments of multi-purpose
lubricants and found that certain products complying with the
25% VOC limit had on average a lower product weighted maximum
incremental reactivity (PWMIR), (0.44 g O3/g product),
than products with a 10% VOC content limit (0.49 g O3/g
product). So certain multi-purpose lubricants created less ozone,
despite having a higher VOC content, because they were using less
reactive chemistry. The alternate compliance option allows companies
to develop formulations that provide air quality benefits
equivalent to the original 10% by weight mass-based VOC limit.
The MIR-based option for multi-purpose lubricants has set a
clear precedent that could be applied to other consumer product
categories. While it may not make sense to move every category
to a reactivity-based control strategy, making the switch for some
may allow manufacturers to meet CARB’s limits more effectively.
While shifting certain categories to reactivity would be a complicated
and arduous process, using better science is always the right
choice that will enable us to find ways to further reduce groundlevel
ozone.
While all of this may seem daunting, at least it isn’t putting a
space station into orbit. Spray
1 Study of Volatile Organic Compound Emissions from Consumer and Commercial Products Report to
Congress. EPA-453/R-94-066-A. March 1995.
2 Cal. Code Regs. Title 17, §§ 94520-28
3 40 CFR Part 59 Subpart E
4 Cal. Code Regs. Title 17, §§ 94507-17
5 Cal. Code Regs. Title 17, §§ 94509 (r)