4.19 Rubber Manufacturing
Categories 46 and 1910
4.19.1 Introduction
Categories 46 and 1910 account for point and area organic emissions from the rubber fabrication industry, including vulcanizing, where raw rubber is compounded by additives and formed into desired shape and cured at required temperature. In the forming steps, large amounts of organic solvent are often used and therefore included in the emissions in this category. There two common ways in which rubber can be manufactured emulsion latex polymerization and emulsion crumb polymerization. It is assumed that the rubber fabrication industries in the Bay Area use emulsion latex polymerization.
4.19.2 Methodology
Point Sources
Point Sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, for which the Air District has issued a permit to operate, e.g. refinery cooling towers. These could also be a collection of similar equipment / sources located across multiple facilities, e.g. reciprocating engines.
During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g. EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.
Further speciation and quality assurance of emissions are performed as a part of the inventory process. The BAAQMD staff also perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids), which ensures consistency in the annual emissions reporting process (CEIDARS) to California Air Resources Board. The last part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes. For those years where no data is available, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using either interpolation or another mathematical approach (see Trends section). Finally, emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated for anomalies that are then investigated and addressed.
Category 46 is considered a point source category and follows the above methodology for emissions estimates.
Area Sources
Category 1910 is considered an area source category since it covers facilities / emission sources that are not directly permitted by the District, and hence not systematically cataloged. Emissions for area source categories are determined using the formula:
Current Year Emissions = Base Year Emission X Growth Profile, and,
Base Year Emission = Throughput X Control Factor X Emission Factor
where,
- throughput or activity data for applicable base year(s) is determined using a top-down approach (e.g. state-, national-level data);
- emission factor is derived from general literature, specific literature and reports, and/or source testing results provided by Air District staff;
- control factor (if applicable) is determined by District and state rules and regulations in effect;
- and, historical backcasting and forecasting of emissions is based on growth profiles as outlined in the Trends section of this chapter
More details on throughput, county distribution, emission factors and controls is provided in the following subsections.
(a) Activity Data / Throughput
Total rubber products production was estimated based on U. S. Census Bureau “Current Industrial Report on Rubber Products” 103. In 2015, it was estimated 16,600 tons were used by area sources (Category 1910).
(b) County Distribution / Fractions
The number of employees within the Rubber Product Manufacturing sector (SIC No. 3262) taken from the 2007 County Business Patterns was used to distribute emissions into the Bay Area counties.
(c) Emission Factors
The organics emission factor was estimated based on AP-42 Table 6-10, for emulsion styrene-butadiene copolymer production 104. The emulsion latex polymerization is done in via batch process, hence it has a smaller usage than emulsion crumb polymerization. An emission factor of 7.54 lbs./ton was derived.
(d) Control Factors
There is no specific District regulations or controls have been instituted on Rubber Products Manufacturing categories. However, the Rubber Products Manufacturing could be regulated under District Regulation 8: Organic Compounds, Rule 2: Miscellaneous Operations (Rule 8-2).
(e) Speciation
The total organic gas (TOG) emissions from Rubber Manufacturing categories are considered all reactive organic gas (ROG). The ROG:TOG ratio is equal to 1.
(f) Sample Calculations
Calculation: (Area Sources, Category 1910):
\[ 16,600\ \frac{\text{ton rubber}}{\text{yr}} \times 7.54\ \frac{\text{lb TOG}}{\text{ton rubber}} \div 2000\ \text{lb/ton} \div 365\ \text{day/yr} = 0.17\ \text{ton/day TOG} \]
4.19.3 Changes in Methodology
There are no changes to methodology for these Rubber Manufacturing categories.
4.19.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
4.19.5 Trends
(a) Historical Emissions / History
Historical emissions for point source emissions (category 46) are derived from source-specific throughput provided by the permitted facility, compiled/reported emission factors, and regulation-based control factors. This information is archived in the BAAQMD’s internal database which is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary, this is the case for years 1991-1992.
The historical growth profile for category 1901 was based on a combination of prior emissions data (back to 1990) and ARB’s Rubber Manufacturing Industry growth profile.
(b) Future Projections / Growth
Forecasting of point source emissions is done based on calculations as shown in the equation below using recently updated growth profiles and a base year of 2020. The growth profiles for the current base year inventory have been verified and updated to represent the most likely surrogate for growing emissions for a given category up to year 2040. Forecasting for point source emissions includes impact of in-place regulations, but does not include estimation of controls that will theoretically be implemented as part of future policy emission targets or proposed regulation and legislation.
\[ \text{PE} = \text{Gr} * \text{Ci} * \text{Ei} \] \(PE\) = projected emissions of pollutant i in a past or future year
\(Gr\) = growth rate by economic profile of industry or population
\(Ci\) = control factor of pollutant i based on adopted rules and regulations
\(Ei\) = base year emissions of pollutant i
Projections of emissions to 2040 for both point and area categories were based on ABAG’s 2017 Manufacturing & Wholesale Employment growth profile.
4.19.6 Uncertainties
The estimated emissions for Rubber Manufacturing area source category (Category 1910) were based on the “Current Industrial Report on Rubber Products”. The values in this report are U.S. totals and an assumed percentage is applied to obtain region specific values. This assumed percentage may not be inline with actual rubber manufacturing in the region and therefore may contribute to uncertainties of emission projections. Refinement of this percentage is planned as a future inventory improvement.
The estimated emissions for category 46 based on a large Rubber Products Manufacturing (Facility 110, Burke Industries) may contribute to an increased uncertainty of Rubber Products Manufacturing point source emissions.
4.19.7 Contact
Author: Michael Nguyen
Reviewer: Ariana Husain
Last Update: November 06, 2023
4.19.8 References & Footnotes
US Census Bureau. 2022. Current Industrial Reports, https://www.census.gov/manufacturing/m3/historical_data/index.html↩︎
EPA. 2020. Emulsion styrene-butadiene copolymer production, https://www.epa.gov/sites/default/files/2020-10/documents/c06s10.pdf↩︎