Area Source Inventory Methodologies
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Area sources are small-scale industrial, commercial, and residential activities that individually emit relatively small amounts of air pollutants but collectively contribute significantly to overall emissions inventories. These sources are not tracked individually like large stationary facilities and are instead estimated using standardized methodologies.
The methodologies provided on this page are used to develop area source emissions inventories. While many methodologies remain consistent over time, updates are made periodically to incorporate improved data, updated emission factors, and revised assumptions. These updates may be implemented for specific inventory cycles, such as the 2023 base year inventory.
Updates for the 2023 Base Year Inventory
The methodologies listed below reflect updates made in support of the 2023 base year emissions inventory. These updates may include revisions to activity data, emission factors, control assumptions, or overall calculation approaches.
Not all area source methodologies are updated for each inventory cycle. Methodologies not listed below have not been revised for the 2023 base year and continue to be used as documented in their most recent available version.
| Category | Last Finalized Update | Update Status | Link |
|---|---|---|---|
| Agricultural Harvest Operations | April 2016 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Agricultural Land Preparation Operations | April 2016 | Updated 2026(documentation forthcoming) | Methodology Documentation |
| Livestock Husbandry and Dairy Cattle Population & Manure Land Application Updates | May 2004 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Livestock Husbandry and Dairy Silage Updates | May 2004 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Unpaved Road Dust, Farm Roads | April 2016 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Unpaved Road Dust, Non-Farm Roads | December 2012 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Entrained Road Travel, Paved Road Dust | March 2021 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Building Construction Dust | September 2002 | Updated 2026 (documentation forthcoming) | Methodology Documentation |
| Residential Wood Combustion | 2026 (Initial Release) | Updated 2026 (documentation forthcoming) | Pending Publication |
| Managed Burning And Disposal, Non-Agricultural Open Burning | 2026 (Initial Release) | Updated 2026 (documentation forthcoming) | Pending Publication |
| Commercial Cooking | 2026 (Initial Release) | Updated 2026 (documentation forthcoming) | Pending Publication |
| Domestic Ammonia | 2026 (Initial Release) | Updated 2026 (documentation forthcoming) | Pending Publication |
Major Categories
Major categories of area source methodologies are listed below. These categories organize related emission source types and provide links to the corresponding methodology documentation.
Misc. Processes, dust, combustion, and other sources
Appendix A Agricultural Activity Based Temporal Profiles
Other Links
Subject Matter Expert Review Panel on Nitrogenous Emissions from Soils
Meetings and Workshops
| Date | Location | Details | Materials |
|---|---|---|---|
| July 11, 2025 10:00 am – 11:00 am PDT | Virtual | The California Air Resources Board (CARB) hosted a public workshop on July 11th to review the Final Report for the Soil Nitrogenous Emissions "Subject Matter Expert Review Panel (SMERP)" Contract (23RD017). The recording of the public workshop as well as the SMERP responses to public questions & comments are now posted under Materials. | - Final Report |
| May 28, 2025 3:00 pm – 5:00pm | Virtual | The California Air Resources Board (CARB) invites you to participate in a public workshop to discuss proposed updates to several area source emissions estimation methodologies. These updates are part of CARB’s ongoing commitment to ensuring emissions inventory methods remain scientifically robust and reflective of the latest data. | - Register - Workshop Notice - CARB Presentation - Workshop Recording |
| May 7, 2024 | Virtual | The California Air Resources Board (CARB) invites you to participate in a public workshop to kick-off the Soil Nitrogenous Emissions "Subject Matter Expert Review Panel (SMERP)” Contract (23RD017). As part of the SMERP, Dr. William Horwath (University of California [UC] Davis), Dr. Whendee Silver (UC Berkeley), Dr. Xia Zhu-Barker (University of Wisconsin -Madison), Dr. Martin Burger (California Department of Food and Agriculture [recently retired]; UC Davis), and Dr. Viney Aneja (North Carolina State University) will conduct a comprehensive review of scientific literature, pertinent databases, and emission estimation methodologies that pertain to nitrogenous emissions from soils. Please join the workshop to find out more from the selected SMERP members discussing plans and process through end of contract in 2025. We welcome your feedback and engagement. | - Register - Workshop Notice - CARB Presentation - SMERP Presentation - Workshop Recording |
February 13, 2025 | Virtual | The California Air Resources Board (CARB) invites you to participate in a second meeting to discuss progress on the Soil Nitrogenous Emissions "Subject Matter Expert Review Panel (SMERP)” Contract (23RD017). The contract will provide CARB with guidance and information on the best scientific evidence for nitrogenous emissions from soils, and will inform the subsequent steps needed to refine the underlying data and methods currently used in our regional air quality modeling to support the State Implementation Plans. Please join the meeting to hear SMERP members discuss progress and plans through the end of the contract in May 2025. We welcome your engagement. | - Register |