4.1 Large and Small Bakeries

Categories 28 and 935

4.1.1 Introduction

Categories 28 and 935 account for particulate matter (PM, PM10, and PM2.5) and total organic gas (TOG) emissions from large commercial bakeries and small bakeries, respectively.

Bread is produced either by sponge-dough process, brews (or liquid sponges) process, or straight-dough process. Commercial bakeries more often use the sponge-dough process, where ingredients are initially mixed, bread dough fermented from 3 to 5 hours, and then baked in ovens at about 450 °F. Bakery products such as sweet rolls, crackers, pretzels, cakes, cookies, doughnuts, biscuits, etc. are either leavened by yeast or by baking powder. Yeast metabolizes the sugars and starches in the dough during fermentation process. The end product of this chemical reaction is primarily carbon dioxide and ethanol (TOG).

The major criteria pollutant emitted from bread baking is primarily ethanol, which is a by-product of the leavening process. Emissions of combustion products from the burning of fuel in the ovens stacks are not considered in this category. Carbon dioxide (CO2) is calculated from the combustion of the ethanol from the bread in an abatement device such as an afterburner. The abatement devices are used on the larger ovens. There is no CO2 emission data from the fermentation process available at this time.

4.1.2 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 final part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes.

Category 28 is considered a point source category and follows the above methodology for emissions estimates.

Area Sources

Category 935 is considered an area source category as it covers smaller, retail bakeries that are not explicitly permitted or individually cataloged by the District. 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

Emissions for category 935 were estimated using the base years of 2011-2015 and applying emissions factors based on compiled source test results from several facilities. Detailed background on the determination of throughput, controls, and emission factors is provided in the following sections.

(a) Activity Data / Throughput

For point source category 28, throughput information was collected from the District’s internal database.

Throughput from larger bakeries is assumed to make up the majority of the total bread market, approximately 63%. Using this assumption and the yearly throughput for point sources, throughput for category 935 on a yearly basis was determined.

(b) County Distribution / Fractions

The county locations and associated emissions of each of the large bakeries were used to distribute countywide emissions. For small bakeries, the number of employees in the large bakeries was subtracted from the total number of employees in each county’s bakeries. This data was found in the U.S. Census Department’s 2015 County Business Patterns22.

(c) Emission Factors

Emission factors for point source category 28 are specific to the facility and device and are provided by the owner/operator.

For those smaller bakeries in the Bay Area (category 935), source test results showed an emission factor of 5.4 pounds ethanol per ton of bread produced.

(d) Control Factors

District Rule 8-4223 was amended requiring control equipment for existing ovens, which commenced operation prior to January 1989. This became effective beginning January 1992. Currently, there is an estimated 90% overall control (for large bakeries) on TOG emissions because of this rule.

(e) Speciation

The speciation applied to TOG to determine ROG is consistent with the size fractions of speciation profiles developed by the California Air Resources Board (CARB) and published on their emissions inventory web-page 24.The total organic gas (TOG) emitted from these three categories is considered to be all reactive (i.e. TOG equals ROG).

The PM2.5/PM and the PM10/PM ratios for this category(s) are consistent with size fractions of speciation profiles made available by the California Air Resources Board (CARB) on their emissions inventory web-page 25. For this category(s), CARB profile number #900 is applied. PM2.5 constitutes 42% of the total PM for this profile, while PM10 constitutes 70% of the total PM.

4.1.3 Changes in Methodology

Emissions for category 935 were forecasted starting from year 2015 using a growth profile based on total population as opposed to a growth profile based on wholesale manufacturing employment.

4.1.4 Emissions

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

4.1.6 Uncertainties

The percentage of retail to commercial bakeries that is assumed is based on a 1987 survey. The amount of smaller bakeries may have significantly increased since this time and this number should be refined to reflect more recent trends.

4.1.7 Contact

Author: Ariana Husain

Reviewer: Sukarn Claire

Last Update: November 06, 2023

4.1.8 References & Footnotes

  1. U.S. Census Bureau: Data. [accessed 2023 Jan 30]. https://www.census.gov/data.html↩︎

  2. BAAQMD. 1994. Regulation 8, Rule 42 - Large Commercial Bread Bakeries. https://www.baaqmd.gov/rules-and-compliance/rules/reg-8-rule-42-large-commercial-bread-bakeries↩︎

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

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

  5. ABAG. Association of Bay Area Governments: Open Data Catalog. [accessed 2023 Jan 30]; https://abag.ca.gov/tools-resources/data-tools/open-data-catalog↩︎