EPA targets hazardous emissions from tire rubber mixing

WASHINGTON—For the tire industry, the emissions associated with rubber processing haven't been subject to hazardous air pollution regulations—at least not specifically through National Emission Standards for Hazardous Air Pollutants, as required by the Clean Air Act.

That is changing.

The U.S. Environmental Protection Agency has proposed amendments to NESHAP, which would provide new hazardous air pollution standards for tire industry rubber processing. It is the only one of the four rubber tire industry sub-categories—rubber processing, tire production, tire cord production and puncture sealant applications—without emissions regulations of some kind.

The proposed rules, detailed in the Nov. 16 Federal Register, are both the result of a cyclical review dictated by the Clean Air Act, as well as litigation brought by environmental advocacy groups.

The proposals are under review, and the comment period for the proposed regulations runs through Jan. 2.

The EPA first established national emissions standards for hazardous air pollutants (HAP) related to rubber tire manufacturing in July 2009. The standards came under review following a lawsuit filed by environmental advocacy groups in 2016, the result of which led to a reevaluation of those standards in 2020.

In April 2020, a decision by the U.S. Court of Appeals in the District of Columbia held that the EPA was obligated to address unregulated HAP when it conducted its eight-year technology review, as required by the Clean Air Act.

That included ensuring regulations were in place for rubber processing within the tire industry.

To establish the proposed rules, the EPA in June 2022, sent a questionnaire to five parent companies operating in the U.S., seeking information related to:

• the rubber tire facilities (location, production background, etc.);
• process and control information for mixers operated at the facilities, including ingredients added and associated components for each combination of ingredients;
• mixer emission data for filterable particulate matter (fPM);
• mixing schematics; and
• emissions control usage.

Following this, the EPA requested emissions data on mixers used at the companies' facilities. Compounds selected for testing included polycyclic aromatic hydrocarbons (PAHs)—aniline, dibenzofuran, hydroquinone, naphthalene and o-toluidine. In addition, data on HAP metals, fPM, and total hydrocarbons were requested.

This data serves as a foundation for the EPA's proposal.

As proposed, the EPA would set maximum achievable control technology (MACT) emission limits related to total hydrocarbons, particulate matter and metal hazardous air pollutants.

For total hydrocarbons (THC), particularly, recently collected data from mixing sites across the U.S. indicate specific HAP are released during the process.

"The emissions data received indicate that THC is emitted from the rubber processing subcategory. Measured THC includes organic HAP, including but not limited to 2-butanone, acetophenone, cumene, hexane, isooctane, methylene chloride, phenol, toluene and xylene, which are the compounds identified by the rubber manufacturing association [sic] (now USTMA) as being emitted during rubber processing in original testing to determine emission factors for the Rubber Tire Manufacturing NESHAP," the EPA proposal states.

"Because the THC measurements, by definition, include all relevant organic HAP (as well as non-HAP), and considering the significant difficulty of measuring numerous individual, speciated organic HAP compounds, we are proposing a MACT standard in accordance with CAA section 112(d)(2) and (d)(3) to limit THC emissions as a surrogate for organic HAP emissions, as described further in section IV.A.2 of this preamble."

The EPA proposes a 15-day rolling average THC emissions limit for mixers of both silica-containing and non-silica-containing compounds. Additionally, an emission limit for THC as a surrogate for organic HAP emitted from rubber mixers for silica-containing and non-silica-containing compounds is proposed.

The proposal calls for a MACT floor THC limit for mixing silica-containing compounds of 9.4 grams per megagram of rubber produced—or about 18,840 pounds per million tons—based on a 15-day rolling average. This, EPA said, applies only to existing rubber processing sources as the costs for upgrades would make it difficult to achieve tougher standards.

For new rubber mixers, the standard would be more stringent.

For mixing silica-containing compounds, the proposed new source THC MACT floor limit is 2.1 grams per megagram of rubber produced—or about 4,210 pounds per million tons.

For non-silica-containing compounds, the EPA proposes a THC MACT floor limit of 45.4 grams per megagram—about 90,800 pounds per million tons. This, the agency said, applies to existing rubber processing sources.

The proposed THC MACT floor limit for new mixers is 17.2 grams per megagram, or about 34,400 pounds per million tons.

When it comes to particulate matter and metal HAP, the EPA data shows no significant difference in emissions between the silica- and non-silica containing compounds mixed. Therefore, for this regulation, there would be a single standard for both compounds.

The age of the rubber processing source also will not be a factor, EPA said.

As proposed, EPA calls for filterable particulate matter measurements of 1.70—or roughly 3,400 pounds per million tons of rubber produced.

For total metal HAP alternative, the EPA is proposing a MACT floor limit of 0.037—about 74 pounds per million tons of rubber produced.

Further details about the proposed regulations, including the data sets on which the standards are based as well as specifics on measurement methodologies, can be found in the EPA's filing.