Statewide Emissions Inventory Program

Purpose and Method

Federal and state laws require the Utah Division of Air Quality to create a comprehensive emissions inventory for point, area, and mobile sources every three years, and annually for some large point sources.

The Statewide inventories summarize emissions for the following criteria pollutants, in tons per year.

• Ammonia (NH3)
• Carbon Monoxide (CO)
• Lead and Lead Compounds
• Nitrogen Oxides (NO)
• Particulate Matter (PM₁₀ & PM_2.5)
• Sulfur Oxides (SO₂)
• Volatile Organic Compounds (VOC)

Hazardous air pollutant emissions are reported for point sources only.

The Statewide Emissions Inventory is posted every three years on our website.  You can also find this information on EPA’s National Emissions Inventory website, along with data from all other 49 states.

Point Sources

Point sources are stationary, commercial, or industrial sources. Several criteria categorize a facility into point source emissions inventory reporting rather than being part of the area source emissions inventory. The point source annual emission inventory for criteria pollutants is collected under authority of Utah Administrative Code. The inventory information is required to track SIP progress, calculate the operating permit program emission fee, fulfill annual reporting requirements to EPA, and supply information to the general public. More information on reporting Point Source Emission Inventories.

Area Sources

Area sources are stationary sources that are too small or too numerous to be treated as individual point sources. The area source inventory is determined from local demographic information, state energy and agricultural statistical data, specific information surveys, and submitted inventories. Source categories range from agricultural dust and outdoor grilling to residential wood combustion, solvent use, and upstream oil and gas facilities. The oil and gas inventory is unique in the area source inventory as rather than using surrogate activity data and generic emission factors, oil and gas companies submit an inventory for their facilities.

Biogenic sources comprise the natural (non-anthropogenic, such as forests, vegetation, and soils) area sources contribution to VOCs and “event” emission sources, such as wildfires, contribute various pollutants to the airshed. Both of these pollution sources are also under the purview of area sources.

Note: The area source inventory remains in development and experiences significant fluctuations. Frequently one inventory is not readily comparable to another due to changing methods, new data sources and new emissions categories.

Mobile Sources

The mobile source inventory includes both on-road and non-road sources. Vehicles traveling on paved roads and highways comprise the on-road sector, which includes cars, light-duty trucks, heavy-duty trucks, and motorcycles. Non-road mobile sources include a wide variety of internal combustion engines and vehicles not operating on roads and highways, such as diesel locomotives, aircraft, airport ground support equipment, and eleven groups of motorized vehicles and equipment found in the non-road module of the current EPA emissions model “MOVES”. These groups include recreational, construction, industrial, lawn & garden, agricultural, commercial, logging, underground mining, miscellaneous oil field equipment, miscellaneous railroad equipment, and marine and pleasure craft.

Emissions are calculated in various ways.

Using MOVES, the user builds input tables that contain local data for on- and non-road mobile sources. Some important groups of input data include vehicle populations, vehicle miles traveled, fuel properties, vehicle age distributions and temperature and relative humidity data. For non-road motorized equipment, similar data is collected, including equipment populations, fuels, hours and months of operation, etc.

FAA’s Aviation Environmental Design Tool (AEDT) is used to estimate emissions for aircraft exhaust, ground support equipment (GSE), and aircraft auxiliary power units (APU) which are associated with aircrafts’ landing and takeoff (LTO) cycle. LTO data were available from both state, local, tribal agencies and FAA databases.

What is the difference between air monitoring data and emissions inventory data?

Air monitoring data shows air pollution levels collected from monitoring stations throughout the state, while emissions inventory data is a summary of pollutants released in Utah throughout the year. Air monitoring data is expressed as a concentration, such as µg/m3 (micrograms of pollutant per cubic meter of air) or ppm (parts per million), whereas emissions inventory data is expressed as tons/year.

Because the units of measurement are different, it is challenging to compare the two data sets; this means it is difficult to compare what we think should be in the air (inventory) to what is actually in the air (monitoring). While there is currently not a comprehensive comparison of the two data sets, in specific situations, the division’s air modeling team runs inventory data through complex computer models to simulate how it would look in real time.

Questions?

• Email airinventory@utah.gov