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Northern Wasatch Front Ozone Emissions Inventory

Use the Interactive Inventory to explore different emission sectors and sources (SCCs).

Inventory address

Screenshot: Northern Wasatch Front VOC and NOx Inventories

What is summertime ozone?

You’re probably familiar with the Wasatch Front’s wintertime PM2.5 pollution, but Utah’s urban center also experiences harmful air pollution – ozone – during the summertime. Ozone is a highly reactive gas that causes damage to human lung tissue. Ground-level ozone is generated when precursor pollutants – Volatile Organic Compounds (VOCs) and Oxides of Nitrogen (NOx) – interact with sunlight. The Northern Wasatch Front region experiences ozone concentrations that exceed Environmental Protection Agency’s (EPA) air quality thresholds.

Bar Graph showing the Number of Days 8-Hour Ozone Daily Max Greater Than 0.070 ppm in Salt Lake City 2000-2022
zone exceedance days in the Wasatch Front.


What is Utah’s responsibility to mitigate ozone?

In August 2018, the EPA designated sections of the Wasatch Front as a nonattainment area for ozone based on the 2015 National Ambient Air Quality Standard of 70ppb. The area includes Salt Lake, Davis, as well as portions of Weber and Tooele counties. Since the Northern Wasatch Front failed to meet the 70ppb threshold by August 2021, the area was bumped up to “Moderate” nonattainment status. As part of this more stringent designation, Utah is developing and will submit a State Implementation Plan (SIP), which includes a description of how the state will reduce emissions in order to meet the air quality standard.

As part of the SIP process, the State of Utah has developed inventories of emissions in the Wasatch Front which can be used to explore and identify various emission sources. Rules can then be adopted to help reduce emissions from these sources, which would count towards reductions in pollutants required for the SIP. 

Utah map highlighting the Northern Wasatch Front Non-attainment Area

Why focus on VOC emissions?

For this round of the SIP the Clean Air Act requires us to focus on VOCs. DAQ has also identified VOC reductions as being very important for reducing ozone formation in the Wasatch Front when compared to NOx reductions alone. If the area is further designated from “Moderate” to “Serious” status, NOx reductions will be considered along with further reductions in VOC emissions.

Where do our emissions occur?

You can see in the video below VOC emissions are most concentrated in densely populated and urban areas, and peak during the day. Summertime NOx emissions are associated more with traffic corridors and the timing of traffic throughout the day.

What VOC reductions are required?

The Clean Air Act requires that we reduce our daily VOC emissions by 15% from our 2017 emissions inventory compared to 2023, when the area is supposed to attain the standard. This means that the State is aiming to reduce daily VOC emissions by ~7 tons per day during the summertime ozone season. Study of the 2017 emissions inventory is crucial to making accurate VOC emissions reductions.

What VOC controls already exist?

Many sources of pollution are already regulated through past SIPs and other rulemaking efforts.

Use this chart to explore different levels of emissions controls and reductions applied to area sources. Note that this chart only applies to area sources; nonroad mobile, onroad mobile, and point sources are not displayed.

  • Potential to Be Controlled: These emissions sources are not yet subject to emissions control measures or have the potential to be further controlled.
  • No Further Action: These emissions sources are already subject to the best available control measures or other emissions reduction rulemaking. No further action can be taken to reduce even more emissions.
  • No Feasible Controls Known: These emissions sources are either technologically impossible to control, or they are economically infeasible to control.

What is an Inventory?

An emissions inventory is a detailed accounting or estimate of air emissions from a wide array of sources. Our inventory is broken down into sectors of similar emission types: 

  • Solvents from area sources
  • On-road and non-road vehicles
  •  Nonpoint (area) 
  • Large point sources
  • Airports 
  • Rail and train emissions 
  • Agriculture and electric generating units 

Sectors are broken down further into individual emission types called Source Classification Codes (SCC’s) and can include things like lawnmowers, natural gas used in homes, and many more. It is important to remember an inventory is a snapshot in time, representing our best guess as to the emissions at the time the inventory was compiled. It is always improving and evolving.


Ryan Bares (rbares@utah.gov)
Lexie Wilson (lexiewilson@utah.gov)

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