MIR: What is it and why should you care?

Written on: July 1, 2019 by Nicholas Georges

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 ground-level 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 ground-level 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)