6.16 Sterilizer Venting

Categories 92 and 1577

6.16.1 Introduction

Categories 92 and 1577 account for organic emissions (TOG and ROG) from medical sterilizers in the Bay Area. Ethylene Oxide is used extensively at large medical facilities in equipment sterilizers as well as in fumigators for the food industry due to its ability to kill microbes in difficult to reach places.

6.16.2 Methodology

Point Source

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-42214 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 92 is considered a point source category and follows the above methodology for emissions estimates.

Area Source

Category 1577 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

Most of these sources are now permitted sources due to the implementation of Regulation 11, Rule 9 in 1989215. Therefore, the amount of area source emissions is estimated to have dropped to 1050 pounds of sterilizer gas.

More details on throughput, county distribution, emission factors and controls is provided in the following subsections.

(a) Activity Data / Throughput

Throughput for Category 1577 or area sources is estimated to be at 1050 pounds of sterilizer gas used annually. Most of the ethylene oxide activity sources are now permitted sources due to the adoption of 1989 Regulation 11, Rule 9, by the Air District.

(b) County Distribution / Fractions

For area source category 1577, county usage distribution is based on population. For point source category 92, county usage distribution is determined by location provided by permitted sterilizer sources.

(c) Emission Factors

The emission factor used for ethylene oxide category 1577 is 1, assuming 100% of ethylene oxide evaporates during use. Emission factors for category 92 (a point source) are specific to source and facility and are provided either by the operator or estimated using published factors in literature such as EPA’s AP-42.

(d) Control Factors

Ethylene Oxide is suspected of increasing the risk of stomach cancer and leukemia in humans, because of this risk, the District adopted Regulation 11, Rule 9 on November 1, 1989. Based on the current base year emissions data, the overall emission control efficiency is estimated at 98.90%.

(e) Speciation

The ROG/TOG ratios applied to this category or this group of related categories are based on an Air District internal speciation profile. Multiple data sources have been used for developing speciation profiles, such as Air District-approved source tests, TOG speciation ratios used by other regional air quality agencies, and relevant literature including latest speciation profiles developed by CARB216 and the US Environmental Protection Agency217. For this category or group of categories, ROG constitutes 100% of TOG.

6.16.3 Changes in Methodology

No changes to methodology were made in this version of the base year emissions inventory.

6.16.4 Emissions

A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.

6.16.6 Uncertainties

Factors that can contribute to uncertainties for these categories are inaccuracies or errors in reporting of activity data by the individual operator or facilities that can intern lead to inaccurate emissions estimates.

6.16.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Update: November 06, 2023

6.16.8 References & Footnotes

  1. USEPA. Document AP-42. Compilation of Air Pollutant Emissions Factors. https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors↩︎

  2. BAAQMD. Regulation 11 - Rule 9. https://www.baaqmd.gov/rules-and-compliance/rules/reg-11-rule-9-ethylene-oxide-sterilizers↩︎

  3. ORGPROF. CARB. 2022. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎

  4. SPECIATE. USEPA. 2022. https://www.epa.gov/air-emissions-modeling/speciate↩︎

  5. The Association of Bay Area Governments (ABAG). Open Data Catalog. https://abag.ca.gov/↩︎