Analyze This: Not all races saw equal improvements in this air pollutant | Science News for Students

Analyze This: Not all races saw equal improvements in this air pollutant

Levels of NO2 in air fell overall from 2000 to 2010, but not equally for all neighborhoods
Nov 1, 2017 — 6:30 am EST
traffic pollution

U.S. levels of nitrogen dioxide (NO2), a common traffic-related air pollutant, have fallen. However, neighborhoods where most residents are people of color tended to see the smallest improvements, new data show.


On average, people in the United States were breathing lower levels of a common air pollutant in 2010 than 10 years earlier. That's the conclusion of a new study. It compared how pollution levels and the racial makeup of residents varied by neighborhood. And it did that for every neighborhood in the continental United States. To do this, scientists used data from the U.S. Census, from satellites and from air-quality stations.

The pollutant, nitrogen dioxide (NO2), can cause breathing problems. So a decrease is good news. However, the study also found that people of color tended to be exposed to more of this pollutant than were whites at both time periods.

Story continues below video.

This video shows how levels of one air pollutant (NO2) changed between 2000 and 2010 for different racial groups in the United States.
University of Washington

This surprised researchers. “There are [differences] in exposure to air pollution that are persisting over time,” says Lara Clark. She is a graduate student in engineering at the University of Minnesota in Minneapolis. Her team published its findings September 14 in Environmental Health Perspectives.

Air pollution can have a direct impact on health. NO2, in particular, irritates the lungs. So breathing it can worsen lung diseases, such as asthma. This pollutant also can cause coughing, wheezing and difficulty breathing.

The main source of NO2 in U.S. air is the burning of fossil fuels. Vehicles powered by gasoline or diesel fuel often are the most common source of this pollutant. This tends to be especially true in cities. Previous research had suggested minority groups and people in low-income households were most likely to live near roads with the most traffic, and therefore the most NO2.

Because NO2 can harm health, governments have acted to cut how much is emitted into the air. Clark’s team wanted to measure how effective U.S. programs had been.

They started by creating a computer program to estimate air pollution from 2000 to 2010 on the neighborhood scale. This computer model combined satellite, air-quality and land-use data (information on where there are roads, houses and businesses) to estimate local pollution levels. The program also used census data to identify the race of the residents in each neighborhood.

Exposure to NO2 decreased for all neighborhoods, the data show. However, neighborhoods that were majority white tended to see bigger reductions in NO2 levels than did those where a greater share of the residents were people of color.

“When it comes to how much NO2 a person breathes, it’s still race that matters most,” says study author Julian Marshall. He is a civil and environmental engineer at the University of Washington in Seattle.

Marshall says that this team’s work could provide the know-how to help provide environmental improvements that would help everyone equally.

NO2 concentration in parts per billion (ppb)20002010
People of color17.6 ppb10.7 ppb
Whites12.6 ppb7.8 ppb
bar graph showing air pollution inequality data
This graph is also a representation of the data from the table above. Both show how neighborhood NO2 concentrations dropped over a decade.
Source: L. Clark, et al/Environmental Health Perspectives 2017; Credit: L. Steenblik Hwang

Data dive: 

1. How did exposure to NO2 increase or decrease for each group of people from 2000 to 2010?

2 How much more NO2, by percentage, polluted neighborhoods in 2000 where a majority of residents were people of color? What about in 2010?

3. As seen in the video, researchers also studied variables such as age, education level, income level and race or ethnicity. Can you think of other variables that might be useful for comparisons in such a study?

Beyond the data:

1. Low-income people and people of color are more likely to live near major roads, with more traffic — and therefore more pollution. Why is this? In a group, brainstorm to come up with a list of at least three possible reasons.

2. The engine in an electric car does not produce the same air pollution that a gasoline-powered engine does. The number of electric cars is expected to increase in the future. How might this affect air pollution levels? Will the inequalities from one neighborhood to another that exist today still be likely to exist 10 years from now (assuming most people do not move)? Explain your reasoning.


Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Power Words

(more about Power Words)

asthma     A disease affecting the body’s airways, which are the tubes through which animals breathe. Asthma obstructs these airways through swelling, the production of too much mucus or a tightening of the tubes. As a result, the body can expand to breathe in air, but loses the ability to exhale appropriately. The most common cause of asthma is an allergy. Asthma is a leading cause of hospitalization and the top chronic disease responsible for kids missing school.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

combustion     (adj. combustible ) The process of burning.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

engine     A machine designed to convert energy into useful mechanical motion. Sometimes an engine is called a motor. 

engineering     The field of research that uses math and science to solve practical problems.

fossil fuel     Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed in the Earth over millions of years from the decayed remains of bacteria, plants or animals.

nitrogen dioxide     A gas ­— often abbreviated as NO2  — that has become an important pollutant in urban air. Most of this gas in the Earth’s lower atmosphere has been released by human activities. Gasoline- and diesel-fueled vehicles are among the most common sources of NO2 in cities. Coal- and natural-gas-burning power plants also can emit regionally high amounts. This pollutant can cause breathing problems and aggravate lung-related diseases such as asthma. NO2 is among the pollutants that contribute to the formation of smog and acid rain.

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

population     (in biology) A group of individuals from the same species that lives in the same area.

wheezing    The chest sounds associated with labored breathing. They can sound like a whistling or rattling, and develop when something obstructs some of the air passages.

Further Reading

WEBSITE: U.S. Environmental Protection Agency. Nitrogen dioxide (NO2) pollution.

WEBSITE: U.S. Environmental Protection Agency. Air quality guide for nitrogen dioxide. Last updated June 23, 2016.

JOURNAL: L. Clark et al. “Changes in transportation-related air pollution exposures by race-ethnicity and socioeconomic status: Outdoor nitrogen dioxide in the United States in 2000 and 2010Environmental Health Perspectives. Published online September 14, 2017. doi:10.1289/EHP959.