CEPAM

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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 taken on March 9, 2022, from CEIDARS. 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.