Introduction

    This document serves as the Bay Area Air District’s methodology for estimating greenhouse gas (GHG) emissions over the nine-county San Francisco Bay Area. It presents emissions estimation methodologies for most major and minor GHG sources in the Bay Area including permitted stationary sources (often called 'point' sources), non-permitted stationary sources (often referred to as 'area' sources) and mobile sources (both on-road and off-road). The methodologies documented here can be accessed via the Table of Contents on the left side of the page. Methodologies are organized into individual chapters under the main classification sectors - Transportation, Industrial, Electricity Generation, Commercial + Residential, Waste Management and Agriculture.  Within a sector-type, different chapters represent methodologies for different process- and source-types. Certain processes and sources cut across economic sectors and their methodologies are covered under 'Multi-sector Sources' in the end. Each chapter in the Table of Contents details the specific methodology applied to individual source categories, following CARB’s guidelines for emission estimation documentation:

    • Scope – Defines the emission inventory codes (EICs) applicable to the source category covered in the chapter.
    • Introduction – Provides an overview of the emission source category and its significance within the inventory.
    • Methodology – Provides a written description of the emissions estimation calculation.
    • Activity Data – Describes the datasets and sources used to determine activity data or throughputs.
    • County Distribution/Fractions – Describes how activity data or throughputs are distributed to each county, including any methods used to estimate the fraction of Solano and Sonoma County activity occurring within the Bay Area Air District jurisdiction.
    • Emission Factors – Lists emission factors for each pollutant applied in calculations, including their sources and justifications.
    • Control Factors/Emission Controls – Lists applicable Bay Area Air District rules and regulations for the source category covered in the chapter, along with estimated emissions reductions by pollutant.
    • Sample Calculations – Provides a sample calculation to demonstrate the methodology’s application.
    • Assessment of Methodology – Summarizes the overall approach for the current and all previous base year emissions inventories.
    • Emissions – Includes a table showing base year emissions by EIC and county for each applicable pollutant.
    • Trends – Includes a timeseries figure showing estimated historical and projected emissions by EIC.
    • Temporal Activity – Includes a table on how emissions vary on an hourly, daily, weekly, and monthly basis.
    • Uncertainties – Identifies key uncertainties/assumptions and their potential impact on emissions estimates.
    • References – Lists the data sources, models, and literature used in the methodology.

    User Notes

    • To export the document as a PDF, use your browser’s Print function (Ctrl + P or Command + P) and select “Save as PDF” as the destination. Interactive elements, such as tables and figures, will automatically expand and reformat for optimal print layout.
    • Use the Table of Contents on the left side of the page to navigate between chapters. Each chapter header is a link that will direct the user to the selected chapter. The glossary contains common abbreviations used throughout the methodology document.
    • Alternatively, use the search bar above the Table of Contents to search by EIC, category description, or chapter name. Searches that match EICs, categories, or chapters covered in this document will appear in a dropdown list. Selecting an entry will direct the reader to the associated chapter.
    • A button located to the right of the Table of Contents allows readers to collapse and expand the Table of Contents panel. Clicking the button collapses the panel to maximize the space available for reading the main text. Clicking the button again re-expands the panel to allow users to navigate between chapters. The button also updates its direction indicator (left or right arrow) based on whether the panel is currently collapsed or expanded.
    • Each chapter page includes a collapsible floating navigation button located in the upper right corner of the screen. Clicking the button reveals a list of section headers specific to the chapter currently being viewed. Clicking on a header link will automatically scroll the page to the corresponding section. The list of section headers can be collapsed again by clicking the button a second time.
    • Tables for the Scope, County Distribution/Fractions, Emissions, and Temporal Profiles sections are rendered as interactive JavaScript data tables with the following functions:
      • Sorting: to sort by a specific column, click on the column header once to sort in ascending order (A-Z or smallest to largest) and twice to sort in descending order (Z-A or largest to smallest).
      • Searching: for tables longer than 10 rows, readers can use the search bar at the upper right corner of the table to search for specific category IDs or descriptions.
      • Pagination: for tables longer than 10 rows, only the first 10 rows show by default. To download the entire table as a csv file, click the button at the upper left corner of the table. To search the table for specific terms (e.g. EIC, description), use the search bar at the upper right corner of the table. To navigate to the next or previous page of the table, use the selections at the bottom right corner of the table. The bottom left corner of the table shows the total number of entries in the table and which entries are currently being shown.
    • The trends figure in each chapter is an interactive HTML element where users can hover the mouse cursor over trend lines to view additional details such as full EIC description and exact emissions values.

    Accessibility

    This document has been structured in alignment with the accessibility requirements of the Americans with Disabilities Act (ADA) and the Web Content Accessibility Guidelines (WCAG 2.1). It includes semantic HTML elements and ARIA landmarks to support screen readers and other assistive technologies, ensuring that all users can navigate and understand the content effectively. Headings follow a logical hierarchy to enhance readability, and tables are properly labeled with captions and scoped headers to provide clear context for tabular data.

    Images throughout the document include descriptive alternative text (alt attributes), making visual content accessible to users with visual impairments. All interactive elements are keyboard-navigable, and data tables use accessible JavaScript libraries that support screen reader compatibility, adjustable display options, and intuitive navigation. The visual design also adheres to recommended color contrast ratios to ensure readability for users with low vision or color blindness. These features work together to make the content inclusive and accessible to a broad audience.

    Contact

    For any questions regarding the contents of this document, please contact the Bay Area Air District’s emissions inventory team at aim@baaqmd.gov. For any issues regarding the website, please contact the webmaster at ntang@baaqmd.gov.