35 Years


Air pollution has been a major topic and cause of concern for the residents of Salt Lake City. Known as “the inversion," the mountains surrounding Salt Lake City frequently disappear behind a curtain of smog during summer and winter seasons. The smog is a result of the pollution trapped by the unique topographic feature of the Wasatch area.

The Air Quality Index (AQI), developed by the Environmental Protection Agency (EPA), is often used to measure air quality. It is calculated based on the pollution levels of five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide (CO), sulfur dioxide(SO2), and nitrogen dioxide(NO2). AQI relates the general health effects associated with different pollution levels, as well as the necessary precautionary steps to take when the air pollution levels become alarmingly high. Starting from 1980, EPA has been calculating and publishing AQI, along with the pollution levels of the five major air pollutants. For each of these pollutants, EPA has established national air quality standards to protect public health. The AQI Levels and their color coordination are shown in the chart below.

This is a visual study of the air quality data of Salt Lake City published by the EPA (www.epa.gov) from 1980 to 2014. The purpose is to visually examine the air quality of Salt Lake City, and perhaps more importantly, its developing trend in the last decades.

Air Quality Index (AQI) Levels and Colors

Levels of Health Concerns



 Unhealthy for Sensitive Groups


 Very Unhealthy


Numerical Value

0 to 50

50 to 100

101 to 150

151 to 200

201 to 300

301 to 500

First, the color code used in the visualization is based on the standard established by the EPA. EPA developed a color-coded system to make it easy for the general public to understand how air quality relates to public health. Green means healthy air, yellow means moderate, etc. This colored AQI is then visualized on a yearly basis, demonstrating the seasonal changes of AQI from 1980. The EPA data also includes the major pollutant source on a daily basis. The composition of the pollution shows the amount of days for each pollutant being the main source of pollution within a year.

Then, to examine the long-term trend, the daily AQI is averaged over each year, resulting in yearly AQI. This is demonstrated in the yearly average graphic. It is clear that there has been a decline of the yearly AQI from 1980 to 1997, after which it remains roughly at a constant level. One can even argue another small decline trend starting from 2007. Since smaller AQI value means healthier air, this demonstrates that the air quality in Salt Lake City has become better from 1980 to 1997. After 1997, the air quality in Salt Lake City has remained roughly at the same health level, with even a small trend towards healthier levels from 2007 to date. This is contrary to popular public opinion -- the air quality in Salt Lake City has become steadily worse in the last decade. This visual study clearly demonstrates that this is not the case. Since the population and industry have been growing in Salt Lake City (population grew 5.2% between the year 2000 and 2013, according to city-data.com), especially after the 2002 Winter Olympics, this suggests that whatever counter measures that have been employed in Salt Lake City to create cleaner air have been having effects and offsetting the increasing pollution level. On the other hand, it should also be recognized that no clear improvement of the air quality has been achieved in the last decade.

The pollution composition is also demonstrated on a yearly basis, using the yearly averaged percentage levels of the five major air pollutants. Evidently SO2 was the major component of the air pollution during the 1980’s. From the early 1990’s, there was a sharp decline of SO2. This corresponds directly to the overall air quality improvement in the yearly AQI chart. Particle pollution, also known as particulate matter (PM), is visualized in a slightly different way. PM in the air includes a mixture of solid and liquid droplets. EPA only started to track PM10 (particles less than 10 micrometers in diameter) from 1987. And starting from 1997, the EPA began to track PM2.5 (particles less than 2.5 micrometers in diameter), along with PM10. From the chart, it is obvious that the air pollution composition has changed over the last decades. The major pollutant in recent years is ozone, as opposed to SO2 in the 1980’s. Another major pollutant is PM, which in recent years consists almost entirely of the smaller particles PM2.5. Although the relatively larger particles measured by PM10 have virtually disappeared, it should be noted that PM2.5 can have worse health effects than the bigger PM10. The smaller particles are lighter and they stay in the air longer and travel further. PM2.5 is made up things that are more toxic, and it may be the air pollutant that most affects people's health (source: airinfonow.org). Today, the air pollution in Salt Lake City is dominated by ozone, PM2.5 and No2.

Environmental policy involves the creation and the implementation of state and federal environmental laws to protect and improve air, land and water quality. Federal environmental policy is enforced by the U.S. Environmental Protection Agency (EPA), which regulates air and water quality, the U.S. Bureau of Land Management, the U.S. Forest Service and the U.S. Fish and Wildlife Service (FWS), among others. State environmental policy is made by the Utah State Legislature and enforced by state agencies through rules and regulations. Utah Environmental regulatory programs are mainly administered by the Utah Department of Environmental Quality (DEQ). DEQ administers environmental programs authorized by state statute as well as federal environmental programs for which the state has delegated authority from EPA under the Clean Water Act, the Clean Air Act and the Resource Conservation and Recovery Act.

Environmental legislation had huge impacts across America resulting in the cleaner air and cleaner water that we enjoy today. The visualization of pollution in Salt Lake Valley clearly demonstrates this. The timeline below highlights some of the major environmental policies between 1980 and 2015. Although the air quality has not been getting worse in the last decade, Salt Lake City is still facing a lot of air-quality related issues. Recently, "Utah ranks No. 2 out of 56 states and territories nationwide for total toxic releases per square mile", according to EPA (source: KSL, January 21st, 2015). The government, the corporations, and all residents of Utah still need to work hard to make this nature lover's heaven a better place to live.

Highlights of Utah Environmental Law
Environmental policy in Utah
Utah Environmental Handbook
Utah State Legislature Histories
EPA Laws & Regulations

  1. 1986

    [Utah]Limits on Stringency of Utah Environmental Regulations

  2. 1987

    [EPA]Water Quality Act (Clean Water Act amendments)

  3. 1989

    [EPA]Oil Pollution Act - Streamlined the EPA's ability to prevent and clean up catastrophic oil spills.

  4. 1990

    [EPA]Clean Air Act Amendments - Title V Permits / Congress required regulation for 194 toxic air pollutants / Acid Rain Program

  5. 1992

    Earth Summit - Signing of the Convention on Climate Change and the Earth Charter, a global pledge to control global warming.

  6. 1995

    [Utah]Utah Environmental Self-Evaluation Act

  7. 1996

    [Utah] Environmental Health Scientist Amendments signed by Governor Leavitt

  8. 1997

    [Utah]Utah Voluntary Cleanup Program

    [Utah]Utah Sales Tax Exemption for Pollution Control Expenditures

  9. 2003

    [EPA]Environmental Institutional Control Act

    [Utah]Final authorization for the revisions to Utah's Hazardous Waste Management Program

  10. 2006

    [EPA]Environmental Institutional Control Act Revision

    [Utah]The Utah Environmental Self-Evaluation Act

  11. 2007

    [Utah]Utah joined the Western Clilmate Initiative (WCI)

  12. 2009

    [EPA]Regulate greenhouse gases

  13. 2011

    [EPA]Cross State Air Pollution Rule - Required states to reduce power plant and fine particle emissions

    [Utah]Withdrew from the Western Clilmate Initiative (WCI)

  14. 2012

    [EPA]Set up mercury and air toxic Standards

  15. 2013

    [Utah]Utah government issued $450 million fund to handle nutrient pollution problems with water sources

  16. 2014

    [EPA]Clean Power Plan proposed

    [EPA]New ozone standards esbalished/

    [EPA]The Resource Conservation and Recovery Act

*The visuals are best viewed with non-mobile computers on modern browsers.
data source: epa.gov _ All rights reserved. ©2015