Qualité de l’air à Detroit

How polluted is Detroit?

Detroit is an industrial city located on the Detroit River in the southeastern area of Michigan. It is that state’s largest city. Like other areas of Michigan, Detroit's climate is influenced by the Great Lakes, exhibiting a humid continental climate featuring cold winters and warm or hot summers. Detroit often appears near the top of the list of most polluted cities in Michigan when ranking real-time air quality index (AQI) data, but the degree of air pollution in Detroit varies depending on pollutant and location in the city.

Detroit air quality improved steadily during the 2000s. During the first half of the decade, overall air quality was in the healthier end of the “moderate” AQI range and crossed over into the “good” range by the middle of the decade. Improvements were seen in average total suspended particulates (TSP), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), PM10 (particulate matter 10 micrometers in size or less), and PM2.5 (particles of 2.5 micrometers or less). However, two key pollutants (carbon monoxide and the amount of elemental lead in TSP) did not show any significant improvement, and ozone, while it did improve slightly during the decade, tended to swing between lower and higher levels.¹

Rankings published by the American Lung Association (ALA) illustrate how polluted Detroit is today. In the State of the Air report, metrics for PM2.5 and ozone pollution are examined to provide a general picture of a city’s air quality compared to other cities. In 2020, the Detroit-Warren-Ann Arbor area ranks number 34 out of 228 metropolitan areas for high ozone days: 56 out of 217 for 24-hour particle pollution and 10 out of 203 for annual particle pollution.² This ranking indicates that annual particle pollution in Detroit is in the top five percent of all the cities measured.

Much of the attention given to pollution in Detroit focuses on the southwest section of the city. This area has a reputation for being not only the most polluted region of Detroit but also one of the worst locations for pollution in the entire state of Michigan due to its dense concentration of heavy industry that emits higher levels of harmful particulate matter than in other areas. In particular, environmental studies found the Boynton neighborhood to be the most polluted in Michigan due in part to the presence of an oil refinery there.³

Since Southwest Detroit tends to have the least healthy air in the city, people who are sensitive to air pollution should be especially careful when visiting.

Why is Detroit air quality bad today?

Detroit's nickname, the Motor City, indicates why certain sections of this metropolis have endured poor air quality for years despite signs of improvement compared to decades ago. A combination of pollution sources all converge in Detroit, including heavy industrial facilities, plants powered by coal, and a nexus of transportation corridors. These persistent daily emissions tend to prevent Detroit air quality from reaching healthier levels on the AQI scale.⁴

A pair of coal-fired power plants in Detroit are among the city’s heaviest emitters of sulfur dioxide (SO₂), a harmful air pollutant made up of sulfur and oxygen. Annually, these two plants alone release a combined 34,000 tons of sulfur dioxide into Detroit’s air.⁵ Sulfur dioxide is a by-product of the burning of fuel that contains sulfur (coal, diesel, and oil being common examples). SO₂, a dangerous gas in its own right, converts to sulfates in the atmosphere when gas particles collide and coagulate, contributing to fine particle pollution that causes harm to the lungs.⁶

What causes air pollution in Detroit?

Pollutants emitted by the heavy concentration of factories and vehicles in the southwest section of the city have been cited as a major factor contributing to a reduction in overall Detroit air quality. Southwest Detroit is home to:⁷

• an oil refinery
• a steel mill
• a wastewater treatment plant
• two power plants (one coal-fired, one gas-fired)
• three heavily-trafficked highways
• a six-lane bridge.

Each of these individually contribute high levels of air pollution by themselves, and their combined emissions can lead to unhealthy concentrations of particulate matter in the air. In fact, four of Michigan’s highest emitters of sulfur dioxide and nitrous oxides are clustered primarily around Boynton in Southwest Detroit.⁸ These two oxides sometimes exist as harmful airborne particulate matter that can irritate the lungs and lead to respiratory issues as well as other health problems. In 2014 alone, the oil refinery in that area emitted 430 tons of nitrous oxide, 83 tons of PM2.5, and 211 tons of sulfur dioxide.⁹

Heavy industrial and transportation activity also has an effect on the levels of nitrogen dioxide (NO₂) and volatile organic compounds (VOCs) in the air. When heat and sunlight cause NO₂ and VOCs to react, they create ozone. Ozone is a highly irritating gas pollutant with significant adverse health effects. In general, as levels of harmful gas pollution (NO₂ and VOCs) increase, so too does ground-level ozone, especially during weekdays when industrial and transportation activity are at their busiest.¹⁰

Wood burning can be another factor that causes increased air pollution in Detroit. Many homes burn wood in fireplaces to generate heat, especially during colder months. While this can help reduce heating bills, it can unfortunately cause particle pollution levels to rise. The chillier climate in northern Midwestern states, especially those bordering the Great Lakes like Michigan, Minnesota, Wisconsin, Illinois, Indiana, and Ohio, leads to a greater tendency to burn wood for heat, which can have a negative effect on air quality in Detroit as wind moves pollution around the region.

Is today an Ozone Action Day in Detroit?

Ozone, one of the key components of smog, is a highly reactive and irritating gas pollutant formed in the atmosphere when precursor pollutants, such as NO₂ and VOCs, are present in the air and react after exposure to heat and sunlight.

The majority of ambient NO₂ comes from:

• fossil fuel combustion
• factories
• power plants

Sources of VOCs include not just industrial activity and fuel combustion but also:

• dry cleaners
• chemical solvents
• aerosol sprays
• cleaning products
• stored fuels

The declaration of an Ozone Action Day in Detroit typically comes when weather conditions have a strong probability of resulting in higher ozone, which can be harmful to people’s health.¹¹ An important distinction to remember is that while ozone can be helpful to human health when present high in our atmosphere, as the ozone layer protects our planet from UV radiation), the presence of ozone at ground level is undesirable since it is toxic to breathe and especially dangerous for people sensitive to airborne pollutants.

Instances of Ozone Action Days in Detroit has gone down over the past quarter-century. In total, Detroiters experienced just over three weeks of healthier ozone levels in 2020 compared to 1996, as there have been 22.5 fewer high ozone days.

Note, however, that data from the past two years shows a slight increase in the incidence of high ozone days in Detroit in comparison to other large cities. In 2018, the greater Detroit area ranked 40 out of 227 metropolitan areas for high ozone days, while in 2020, Detroit ranked 34 out of 228.¹² Moving up six spots on this list may not seem like a huge jump, but this indicates that Detroit must still take action to improve ozone pollution.

Is air quality in Detroit improving?

Improvements in Detroit air quality have been inconsistent.

Progress in regards to air pollution has been evident over the past half-century. University of Michigan public health researchers state that air quality in southeast Michigan, where Detroit is located, has undergone significant improvement since the passage of the Clean Air Act five decades ago.

Looking at the most recent 25 years, air pollution levels in Detroit have improved along three important measures. First, Detroiters did not experience frequent unhealthy levels of ozone in 2020 compared to a quarter century ago, with the city experiencing 22.5 fewer high ozone days in 2020 versus 1996.

Two other important measures of Detroit air pollution have also improved. There has been a decrease in 24-hour particle pollution measures, with 23.3 fewer days of high Detroit particle pollution this year compared to the year 2000. Similarly, annual particle pollution levels have decreased as well; this year, compared to two decades ago, has seen a decrease of 8.6 µg/m³. These latter two measures deal with particle pollution – tiny solid and liquid particles in the air that can negatively impact our health and put sensitive individuals at risk if inhaled in high enough amounts for sustained periods of time and even if high concentrations are inhaled during short periods of time, resulting in acute exposure to harmful airborne particulate matter.

Despite improvements, there is still cause for concern. When comparing air quality in the US for over 200 cities, Detroit ranked in the top five percent for annual particle pollution this year. Moreover, four of the highest emitters of harmful oxides in Michigan are located there.

Some measures of Detroit’s air pollution data have seen positive developments compared to decades ago, with levels of ozone and particle pollution improving along three key metrics since the turn of the century. However, certain areas of the city, especially Southwest Detroit, remain troubled by poor air quality. The continued presence of multiple emitters of harmful oxides means that Detroit air quality still faces an uphill battle, and further improvement is needed.

+ Article Resources

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[2] American Lung Association. (2020). State of the Air -- report..
[3] Stateside Staff. (2014, April 15). Southwest Detroit is Michigan's most-polluted area. Michigan Radio.
[4] Ellison G. (2020, April 27). Detroit air pollution levels drop amid coronavirus shutdown. M Live.
[5] Schlanger Z. (2016, March 29). Michigan's air pollution problem is much bigger than the water in Flint. Medical Daily.
[6] American Lung Association. (2020, February 12). Sulfur dioxide.
[7] Searcy S. (2019, April 18). Heavy pollution in southwest Detroit will worsen with the Gordie Howe Bridge. EcoWatch / Nexus Media.
[8] Costley D. (2020, January 9). The blackest city in the US is facing an environmental justice nightmare. The Guardian.
[9] Abdel-Baqui O. (2018, February 9). Pollution and southwest Detroit. Detroit Journalism Cooperative.
[10] Humphrey A. (2020, June 18). Metro Detroit weather: Air Quality Alert as today becomes a scorcher. WDIV ClickOnDetroit.
[11] Public Citizen. (2018, May 17). What is ozone pollution and what is an Ozone Action Day?
[12] CBS News. (2018). U.S. cities with the worst air pollution.