California Air Resources Board

General Questions

What are the origins of the criteria pollutant emissions inventory program and why was it created?

The development and maintenance of the criteria pollutant emission inventory in California was initiated over a half century ago as a response to understand the emission source makeup that causes the renowned air quality problems in the state. This concentration on the emission inventory discipline in California was further heightened by the adoption of the federal Clean Air Act Amendments of 1990 and the tightened ambient air quality standards that coincided. Since that time, as the air quality standards have become increasingly more stringent, emission inventory science has had to mature accordingly, becoming more complex to meet the needs of the inventory clientele—specifically air quality planners and air quality modelers.  The methodologies used as the basis for the emission estimates have had to become more refined, and the systems we use to maintain the emissions data must incorporate state-of-the-art Information Technology to ensure sound data collection, management, processing, and reporting accuracy. On the whole, California has realized dramatic improvements in the air quality as a result of emission reductions resulting from control regulations on the industrial complex and tightened mobile source emission standards; however, there are parts of the state that have not yet met the federal air quality standards; thus the emission inventory will continue to serve as the foundational bedrock for determining key emission sectors of focus to construct the necessary control strategies to attain clean air.

What are different types of emissions sources?

There are stationary point sources, areawide sources, mobile sources, and natural sources of emissions. For more information on emission sources, view this page.

What are the National Ambient Air Quality Standards (NAAQS)?
The EPA sets NAAQS for six criteria pollutants to establish safe levels of air pollution for public health. The pollutants are particulate matter (PM), ozone (O₃), nitrogen oxides (NO_x), sulfur oxides (SO_x), carbon monoxide (CO), and lead. Learn more here.

What is a State Implementation Plan (SIP)?
SIPs are comprehensive plans that describe how an area will attain national ambient air quality standards (NAAQS). Click here for more information.

What is the National Emissions Inventory (NEI)?

The National Emissions Inventory is a comprehensive and detailed estimate of air emissions of criteria pollutants, criteria precursors, and hazardous air pollutants from air emissions sources required by the EPA and released every three years. The NEI is based primarily upon data provided by State, Local, and Tribal air agencies for sources in their jurisdictions and supplemented by data developed by the US EPA and is built using the Emissions Inventory System (EIS) first to collect the data from State, Local, and Tribal air agencies and then to blend that data with other data sources.

Emissions Inventories

What is an emissions inventory?

An emissions inventory is a comprehensive estimate of air pollutant emissions data by source for a specific geographic area during a given time period. 

For example, California Air Districts report stationary and area source data to CARB each year, and CARB reports statewide data to the EPA for the National Emissions Inventory (NEI) every three years.

To learn more about California Emissions Inventories, visit this page.

Why do we need emissions inventories?

State and federal law requires CARB to compile annual emissions inventories. To learn more about the specific laws, click here.

Why are emissions inventories important?

Emissions inventories provide insight into many aspects of air quality management and are used in a variety of applications. The data from emissions inventories helps identify pollutants, sources, and regions of concern. Emissions Inventories are used to develop and monitor pollution control strategies, assess health risks, track pollutant trends, and are also used as inputs in predictive air quality models.

What are speciation profiles?
Speciation profiles are estimates of the chemical composition of emissions and are used in air quality modeling and inventories. Click here for more information.

Where can I get more information on CARB’s area source methodology?

For more information on CARB’s area source methodology click here.

How are emissions inventories prepared?

CARB collaborates with Air Districts to maintain detailed emissions inventories categorized by source and pollutant type. Local air districts are responsible for compiling point source data from facilities and reporting that to CARB, who then performs quality assurance checks to validate the data.

Process for preparing emission inventories:

First, air districts collect data from facilities like industrial plants that emit air pollutants. Districts submit that data to CARB annually to maintain an updated emissions inventory for the state. CARB conducts quality assurance checks on the data and gives feedback to air districts if there are any mistakes or missing information. Once data is deemed issue-free, it gets added to the CEIDARS database by CARB and contributes to the statewide emissions inventory.

How can I view data from CARB’s emissions inventories?

CARB has three interactive web tools that pull and display user-queried data from emissions inventories.

• The Facility Search Tool can be used to query stationary point criteria pollutant and air toxics emissions in a given inventory reporting year, as well as information on facility risk. The tool contains historical and current criteria and toxics emissions data from 1987 and 1996, respectively. Access this tool and learn more here.
• The Pollution Mapping Tool allows users to locate and view emissions of GHGs and now, for the first time, also includes criteria pollutants from large facilities in California. The tool provides an interactive platform where users can select facilities by name, location, or industrial sector; view their reported emissions using maps, charts and tabular formats; and download data. Access this tool and learn more here.
• The CEPAM Standard Emissions Tool contains backcasts and forecasts of point and area emissions sources from 2000 to 2050 using the most current growth and control data available. Access this tool and learn more here.

Where can I find information on reporting requirements for criteria pollutant emission inventories?

For more information on Reporting of Criteria Air Pollutants and Toxic Air Contaminants (CTR), such as CTR facility applicability determination, click here.

Where can I find information on reporting requirements for air toxics emissions inventories?

For more information on AB 2588 Air Toxics "Hot Spots" Emission Inventory Criteria and Guidelines Regulation (EICG), such as Hot Spots Fees, EPA AirToxScreen Review, Toxic pollutants and Risk Information, or the California Toxics Inventory (CTI), click here.

Where can I find information on reporting requirements for greenhouse gas emissions inventories?

Learn more about the California Greenhouse Gas Emissions Inventory Program here.

CEIDARS

What is the California Emissions Inventory Data Analysis and Reporting System (CEIDARS)?

The California Emissions Inventory Data Analysis and Reporting System (CEIDARS) is a database management system developed to house statewide criteria pollutant and air toxics emissions data. The sources in CEIDARS are divided into reporting years and store discrete information about different emissions sources.

CEPAM

What is the California Emission Projection Analysis Model (CEPAM)?

The California Emission Projection Analysis Model (CEPAM) is a time series model projected off of a base year inventory, which is pulled from CEIDARS. It contains backcasts and forecasts from 2000 to 2050, derived from a 2017 base year inventory using a static snapshot taken on March 9, 2022, from CEIDARS. The most current publicly available version of CEPAM can be found here. For more information on CEPAM, click here (link under construction).

What does “growth and control” mean?

CEPAM forecasts emissions for point and area sources using both growth and control data. “Grown” data applies growth profiles which account for how socio-economic and/or demographic behavior has influenced emission changes historically and will influence them in the future. “Controlled” data applies control profiles which account for how regulatory actions affect emission categories or sectors over the implementation life of the rule. The standard emission tool defaults to “grown and controlled”. However, you may also look at emissions that are either only grown or only controlled (add links). 

Where can I find mobile source emissions data?

For mobile sources, CEPAM integrates the emission estimates from CARB's EMFAC2017 and OFFROAD mobile source emission models to produce a comprehensive emission inventory. 

How can I see trends for criteria pollutant emissions over time?

With the CEPAM standard emissions tool, you can view emissions data and filter by season, pollutant, year, source type, and geographic area from the years 2000 to 2050. You can also adjust control and growth constraints on forecasted emissions. Check it out here.

What’s the difference between CEIDARS and CEPAM?

CEIDARS is a database that houses criteria & toxic emissions data statewide. CEPAM is a model that projects emissions trends that pulls data from CEIDARS.

Contacts

I work for an Air District, where can I find more emissions inventory resources?

Please visit this page.

I have an emissions inventory question that isn’t answered here. Who can I reach out to?

Please email the contact email listed in this page for questions about the criteria pollutant emissions inventory. For large information requests, please see the Accessing Public Records page.