California Air Resources Board

Description

This page provides resources for Air Quality Management Districts and Air Pollution Control Districts working with the California Air Resources Board (CARB) on emissions inventory data collection, reporting, and management.

District Resources SharePoint

CARB maintains a dedicated SharePoint site with criteria emission inventory resources for Air Districts. 

The site contains resources such as:

• Emission inventory reporting (e.g. utility tables)
• Contact information
• Growth & control (e.g. growth & control submission guidelines)
• Hotspots Analysis & Reporting Program Emission Inventory Module (HARP EIM)
• Emission Inventory Technical Advisory Committee (EITAC)

Note that you're required to be logged in to your Air District email in order to access the site. You can request access directly through the SharePoint site. CARB staff will review requests to verify district affiliation before granting access.

Emission Inventory District Resources SharePoint

HARP Training Course

A guided course dedicated to learning about the HARP EIM and how to use it is available in the CARB Learning Management System (LMS). The name of the course is “HARP: Air Toxics Reporting”.

To access the course, select the “My Account” button, enter your sign in credentials, and click on “External Student Log-In”. If you do not have an account, select the “Create New Account (External Students)” button. 

Air Quality Training | California Air Resources Board

CEIDARS liaison

CEIDARS liaisons are the main point of contact between the Air Districts and CARB for CEIDARS emission inventory related issues. To find your liaison, click here.

EIC codes

Emission inventory codes (EICs) categorize emissions by economic sector, source type, material use, and sub-categories. Click here to view CARB's EIC table.

Emission Sources in California

California's diverse landscape, industries, and population contribute to various sources of air pollution. CARB, in cooperation with local Air Quality Management Districts and Air Pollution Control Districts, categorizes emission sources into six major sectors:

Stationary Point

Stationary point sources are most often individual facilities that have specific locations. These sources are typically permitted by Air Districts.

Examples: power plants, oil refineries, manufacturing facilities, food processing plants

Stationary Aggregated

Stationary aggregated sources groups sources based off similarity

Examples: gasoline stations, dry cleaners, agricultural pumps, small engines and generators

For more information on how we estimate stationary aggregated emissions, visit Index of Methodologies by Major Category.

Areawide

Areawide sources do not have have a specific location and are spread over large areas.

Examples: consumer products, paved and unpaved roads, fugitive windblown dust 

For more information on how we estimate areawide emissions, visit Index of Methodologies by Major Category.

On-Road Mobile Sources

On-road mobile sources are vehicles that typically operate on roadways.

Examples: passenger cars, light and heavy-duty trucks, motorcycles, buses, motor homes

For more information on the on-road emission inventory, visit the EMFAC page.

Off-Road Mobile Sources

Off-road mobile sources are vehicles and equipment that operate off roadways.

Examples: aircraft, trains, ships, boats, construction equipment, farm machinery, airport ground support equipment

For more information on CARB off-road inventory, visit the OFFROAD page.

Natural Sources

Emissions that are not a result of human activity.

Examples: vegetation, petroleum seeps, wildfires

For more information on CARB off-road models, visit the Natural Source Methodologies page.

What Are Criteria Pollutants?

Criteria pollutants are six common air pollutants that the U.S. Environmental Protection Agency (EPA) regulates under the Clean Air Act. The California Air Resources Board (CARB) works to monitor, control, and reduce these pollutants throughout the state.

Particulate Matter (PM)

Particulate matter (PM) are tiny particles suspended in the air that vary in size, composition, and origin.

Human health effects include respiratory issues, heart problems, and decreased lung function.

Major sources include construction sites, unpaved roads, fires, vehicle exhaust.

Total PM refers to all all particulate matter in the air. PM10 includes particles with a diameter up to 10 micrometers. PM2.5 includes particles with a diameter up to 2.5 micrometers

Carbon Monoxide (CO)

Carbon monoxide is a colorless, odorless gas produced by incomplete combustion of carbon-containing fuels.

Human health effects include reduced oxygen delivery to organs and tissues

Major sources include vehicle exhaust, industrial processes, and residential wood burning

Sulfur Oxides (SOx)

Sulfur oxides are gases produced primarily from fossil fuel combustion at power plants and industrial facilities.

Human health effects include respiratory effects and increased asthma symptoms.

Major sources include fuel combustion, industrial processes, and shipping

Lead (Pb)

Lead is a toxic metal found in older products and some industrial processes.

Human health effects include neurological disorders, particularly in children

Major sources include metal processing, aviation fuel, and waste incineration

Nitrogen Oxides (NOx)

Nitrogen oxides are highly reactive gases formed from emissions from various combustion sources. Nitrogen oxides are precursors to the formation of ground-level ozone.

Human health effects include respiratory inflammation and aggravated respiratory issues

Major sources include motor vehicles, power plants, and industrial boilers

Reactive Organic Gases (ROGs)

Reactive organic gases evaporate into the air and react with other air pollutants. These gases are precursors to the formation of ground-level ozone.

Human health effects include aggravated respiratory issues, throat irritation, reduced lung function

Major sources include motor vehicles, industrial processes, and some consumer products (e.g.paints, cleaning products)

What is CEIDARS

The California Emissions Inventory Data Analysis and Reporting System (CEIDARS) is the database used by the California Air Resources Board (CARB) to store and maintain criteria and toxic pollutant emissions statewide.

This data management system serves as the foundation for the state's air quality planning efforts.

How CEIDARS works

CEIDARS integrates emissions data from multiple sources, which is then utilized for various air quality planning purposes. The system:

• Collects data from local air districts, state agencies, and other sources
• Validates data through quality assurance procedures
  • Automated and manual validation checks
  • Cross-referencing with other data sources
  • Historical trend analysis
• Stores emissions inventories for current and historical years
• Serves the following purposes:
  • Fulfills reporting requirements for state and federal programs
  • Supplies emission data for public-facing tools (e.g. facility search tool)
  • Internal and external data requests
  • Air quality planning
    • CEPAM
      • Supplies emission data to the CEPAM model, which is used for regulatory planning and modeling
    • State Implementation Plans (SIP)
      • Supplies emissions data for demonstrating compliance with federal air quality standards
    • Health Risk Assessment
      • Supplies emission data to evaluate potential health impacts of air pollution
    • Regulation and Progress Tracking
      • Evaluates effectiveness of control measures and provides information for development of new measures

What information does CEIDARS maintain

• Criteria pollutant emissions
  • Particulate Matter (PM)
  • Carbon Monoxide (CO)
  • Sulfur Oxides (SOx)
  • Lead (Pb)
  • Nitrogen Oxides (NOx)
    • Ozone precursor
  • Reactive Organic Gases (ROGs)
    • Ozone precursor
• Toxic pollutant emissions
  • More information
• Temporal profiles
  • How emissions vary by season, day of week, and hour of day
•  Spatial allocation
  • Where emissions occur across the state
• For stationary point sources, CEIDARS maintains the following:
  • Facility identification and location data
  • Device information
  • Process information
  • Control equipment specifications
  • Stack parameters for dispersion modeling

How is CEIDARS structured

The following documents provide information on the structure of CEIDARS: 

• Database Structure
• Data Dictionary

How can I access CEIDARS data

Emissions data from CEIDARS is available through the Facility Search Tool. 

For specific data needs that aren't available through our public tools, interested parties can submit a Public Records Act (PRA) request to access CEIDARS data. For more information on accessing emissions data or submitting a PRA request, please visit our Guidelines for Accessing Public Records page.

Emission inventory reporting

CARB provides annual reporting guidelines for the Air Districts. The following document provides guidelines for the reporting of stationary point criteria and toxic emissions:

• 2025 Emission Inventory Reporting Guidelines

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 is the criteria & toxic emission inventory prepared?

First, Air Districts collect criteria & toxic emission data from facilities like industrial plants. Second, Air Districts submit this data to CARB annually. Third, CARB conducts quality assurance checks on the data and works with the Air Districts to update any data issues. Once the data is issue-free, the data gets added to the CEIDARS database, contributing to the statewide emissions inventory.

Where can I view a map of the 35 Air Districts?

You can view Air District map here. Clicking on a particular Air District will direct you to that District’s landing web page.

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.

Overview

The California Emission Projection Analysis Model (CEPAM) is a sophisticated analytical tool developed by the California Air Resources Board (CARB) to project future emissions of criteria pollutants across the state. CEPAM serves as a critical component in California's air quality planning process.

What is CEPAM?

CEPAM was created to support State Implementation Plan (SIP) development, air quality modeling efforts, and the tracking of SIP progress. It takes baseline emissions data from CEIDARS and projects future emissions based on anticipated growth, control measures, and regulatory impacts. These projections help air quality planners evaluate the effectiveness of existing and proposed control strategies and determine whether California will meet air quality standards in the future. CEPAM is also generally useful for assessing emissions trends for criteria air pollutants over time.

How CEPAM Works

CEPAM uses a comprehensive methodology to develop emissions projections:

1. Baseline Data Integration: Incorporates the most recent quality-assured emissions inventory data from CEIDARS
2. Growth Factors Application: Applies sector-specific growth factors based on demographic and economic forecasts
3. Control Factor Application: Accounts for emission reductions from adopted regulations and control measures
4. Projection Calculation: Calculates future year emissions based on baseline emissions, growth, and controls
5. Scenario Analysis: Develops various scenarios to evaluate different policy options and control strategies

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

Seasonal Attributes

In order to characterize emissions during typical air quality exceedance periods, seasonal adjustment factors (a.k.a temporal factors) are used to apportion emissions into the periods under consideration for air quality planning purposes.

Stationary Point & Area Sources

The following equation is used to calculate the Temporal Factors (TF) that are then used to calculate the summer and winter average daily emissions when applied to the total annual emissions for stationary and areawide sources:     

TF_(r,x) = SEAS_FRAC_(r,x) / (# days/season)

Where:

• SEAS_FRAC: the sum of fractional monthly throughputs for the emission process
• Summer: May – October (184 days)
• Winter: November – April (181 days)
• r: denotes the region
• x: denotes the source category resolution
  • for point sources
    • the resolution is at the FACILITY/DEVICE/PROCESS level
  • for area sources
    • the resolution is at the EIC level

For a summer day:

SUMEMS = EMS × SUMMER_TF

Where:

• SUMEMS: summer average emissions (tons/day for the summer season)
• EMS: annual emissions (tons/year_season)
• SUMMER_TF : temporal factor (summer_season/day)

On-Road Mobile Sources

EMFAC considers tons per day emissions that are impacted by different seasonal conditions. Conditions that change with each season in EMFAC include ambient temperature and relative humidity, summer vs. winter gasoline blends having different Reid Vapor Pressure (RVP), as well as vehicle air conditioner and heater usage. These factors impact pollutant emission rates.

•  Annual Average represents average conditions over an entire year. 
•  Summer and Winter average represent average conditions in these respective seasons.

Off-Road Mobile Sources

For off-road mobile sources, seasonal average inventories are generally calculated from the ground up and the methods differ slightly depending on the emission category.  

Example 1: Ocean-Going Vessels (OGVs)

CARB obtains day to day emissions for all 365 days, based on vessel Automated Information System (AIS) data. 

This allows CARB to simply calculate the annual average and summer and winter seasonal averages in tons per day for OGV.

Example 2: Agricultural Equipment

For tractor category/engine groups, CARB obtains activity data such as the number of hours that the tractor engine groups operate per day throughout the year; for example, operating ~11 hours/day in a given summer month and 3.85 hours/day in a given winter month

From these operation parameters the emissions for (1) annual average; (2) summer average and (3) winter average are compiled directly by summing up the daily emissions for each season.

The associated Temporal Factors (TF’s) that result from these emission estimates are the following ratios:

SUMMER_TF = SUMEMS / AAEMS

WINTER_TF = WINEMS / AAEMS

Where:

• AAEMS: annual average emissions
• SUMEMS: summer average emissions
• WINEMS: winter average emissions

These TF’s are often used for modeling purposes.

CEPAM Tools and Data Access

Current CEPAM Version

The most current publicly available version is CEPAM2019v1.04, which contains backcasts and forecasts from 2000 to 2050, derived from a 2017 base year inventory using a static snapshot of CEIDARS taken on March 9, 2022. The 2017 base year aligns with EPA’s National Emissions Inventory (NEI) reporting year and represents the base year for emission projections that served the SIPs developed for the 2015 70 ppb National Ambient Air Quality Standard (NAAQS) for ozone. This version of CEPAM integrates the emission estimates from CARB's EMFAC2017 and OFFROAD mobile source emission models to produce a comprehensive emission inventory.

View Data by Pollutant Across Year (Standard Emission Tool)

CEPAM’s Standard Emission Tool presents emissions by pollutant across year, which is useful for conducting trend analysis. 

Using CEPAM

The CEPAM tool allows you to explore and analyze emissions data through a user-friendly interface. Here's how to effectively use the tool:

• Select Analysis Parameters: Start by choosing your analysis criteria from the dropdown menus:
  • Season: Choose between annual average emissions or seasonal averages (summer: May–October; winter: November–April)
  • Pollutant: Select one criteria pollutant at a time (TOG, ROG, CO, NOx, SOx, PM, PM10, PM2.5, or NH3)
  • Growth/Control Options: View emissions under different scenarios:
    • "Grown and controlled" (default): Shows projected emissions with both growth factors and control measures applied
    • "Grown only": Shows what emissions would be with growth but without control measures
    • "Controlled only": Shows the effect of control measures without growth factors
• Refine Your Analysis:
  • Time Period: Select specific years or ranges between 2000–2050 to view historical trends or future projections
  • Source Types: Filter by emission source categories (all sources, anthropogenic sources only, stationary, mobile, areawide, or natural)
  • Geographic Area: Narrow down to specific regions (statewide, air district, air basin, or county)
• Viewing Results: Once parameters are selected, the tool generates tables and charts showing emissions data in tons per day based on your criteria. You can:
  • Export data tables for further analysis
  • Compare emissions across different years
  • Identify major contributing sources
  • Evaluate the effectiveness of control measures by comparing "grown only" vs. "grown and controlled" scenarios

View Data by Year Across Pollutant (Source Category and/or Region Tools)

Emissions broken down by source category and by geographic region at the links below are presented by year across pollutant, with the default year set to the 2017 base year emissions. There is an option to start a new query to view emissions for different years, by source category, available in 5-year increments from 2000-2050. If you are interested in viewing emissions for multiple pollutants for a single year, use this tool.

Statewide

The above link presents the CA statewide total emissions of TOG, ROG, CO, NOX, SOX, PM, PM10, PM2.5, and NH3 by source. Data defaults to the base year of 2017 unless you change the inventory year.

District

Air Districts, the regional governing authorities primarily responsible for controlling air pollution from stationary sources, are shown overlayed on a map of California at the link above. Emissions of TOG, ROG, CO, NOX, SOX, PM, PM10, PM2.5, and NH3 are broken down by source for each specific air district. Data defaults to the base year of 2017 unless you change the inventory year.

Air Basin

Air Basins, generally categorized as having similar meteorological and geographic conditions throughout, are shown overlayed on a map of California at the link above. Emissions of TOG, ROG, CO, NOX, SOX, PM, PM10, PM2.5, and NH3 are broken down by source for each specific air basin. Data defaults to the base year of 2017 unless you change the inventory year.

County

The 58 CA counties are outlined on a map of California at the link above. Emissions of TOG, ROG, CO, NOX, SOX, PM, PM10, PM2.5, and NH3 are broken down by source for each county. Data defaults to the base year of 2017 unless you change the inventory year.