CA Mobile Source Emissions Inventory Modeling Tools
Description
CARB’s MSEI (Mobile Source Emissions Inventory) Modeling Tools page is a hub for California’s official mobile?source emissions models—including EMFAC (on?road vehicles), OFFROAD (off?road equipment), and related utilities. These tools estimate emissions of criteria pollutants, toxics, and greenhouse gases from cars, trucks, buses, construction equipment, lawn and garden equipment, and more, and are used for SIPs, conformity, CEQA, and other regulatory and planning analyses.
Questions this resource can help answer
What are current and future on?road and off?road emissions (NOx, PM, VOC, CO?e, etc.) in my region?
How will new regulations or control programs change mobile?source emissions over time?
Which vehicle or equipment categories are the largest contributors to a given pollutant?
How do emissions under different scenarios (e.g., with vs. without a clean truck rule, fleet electrification) compare?
What mobile?source emissions should be used as inputs to regional air quality or climate modeling for California?
How do I use this resource?
Go to the MSEI page and select the model that matches your need:
-EMFAC for on?road vehicles
-OFFROAD for off?road equipment
-Other listed tools/utilities as needed.
Download the model and documentation (user guide, tech support docs, release notes).
Configure according to the instructions (often Windows?based with specific runtime requirements).
Prepare inputs (calendar year, region, scenarios, activity/vehicle mix if you’re overriding defaults).
Run base and alternative scenarios and export emissions by pollutant, vehicle/equipment type, and geography for use in inventories, CEQA, or air quality modeling.
Pro tips
Use the latest version of each model; agencies generally require current versions for official work.
Start with default scenarios for your region/year and only override inputs when you have solid local data.
Carefully match geography and year (e.g., specific air district, county, or statewide; 2024 vs 2030).
Document every non?default assumption (fleet composition, activity modifiers, controls) for review.
For CEQA or project work, align your EMFAC/OFFROAD runs with CalEEMod or other tools if both are used.
If outputs will feed into dispersion or photochemical models, coordinate with modelers on the needed format and resolution.
Resource information
Technical specifications
Each model multiplies activity by emission factors for each source category and sums across types, pollutants, and regions. EMFAC covers on?road fleets by vehicle class and speed/road type; OFFROAD does the same for equipment categories. Inputs and assumptions are based on surveys, registration data, fuel usage, and test programs, and are periodically updated to reflect new regulations and data.
