Despite their invisibly small size, ultrafine particles have become a massive concern for air pollution experts. These tiny pollutants — typically spread through wildfire smoke, vehicle exhaust, industrial emissions and airplane fumes — can bypass some of the body’s built-in defenses, carrying toxins to every organ or burrowing deep in the lungs.����

New research from the 91���� found that those effects aren’t felt equitably in Seattle. The most comprehensive study yet of long-term ultrafine particle exposure found that concentrations of this tiny pollutant reflect the city’s decades-old racial and economic divides. ��

The study, ��in Environmental Health Perspectives, also found that racial and socioeconomic disparities in ultrafine particle exposure are larger than those observed in more commonly studied pollutants, like fine particles (PM 2.5) and nitrogen dioxide (NO2).��

The study used mobile monitoring — a car loaded with air pollution sensors driving around the city for the better part of a year — to examine long-term average levels of four pollutants: soot (or black carbon), fine particles (PM 2.5), nitrogen dioxide (NO2) and ultrafine particles. Researchers found the highest concentrations of all four pollutants on census blocks with median household incomes under $20,000 and those with proportionately larger Black populations. ��

Disparities in concentrations of ultrafine particles — which are less than 0.1 micron in diameter, or 700 times thinner than the width of a single human hair — were especially stark. Blocks with median incomes under $20,000 had long-term UFP concentrations 40% higher than average. Blocks where median incomes are over $110,000, meanwhile, saw UFP concentrations 16% lower than average.����

“We found greater disparities with this pollutant of emerging interest, a pollutant that hasn’t been well-characterized. That’s very interesting,” said senior author , a 91���� professor in the Department of Environmental and Occupational Health Sciences. “Our work has shown the highest ultrafine particle concentrations are north of the airport and below common aircraft landing paths, downtown, and south of downtown where there are port and other industrial activities.”��

The study also found that modern-day air pollution disparities mirror Seattle’s history of redlining, the racist practice that denied racial minorities and low-income residents access to bank loans, homeownership and other wealth-building opportunities in more “desirable” areas. The practice shaped American cities throughout the early 20th century, building a foundation of segregation and environmental racism.��

Today, neighborhoods once classified as “hazardous” are still exposed to higher concentrations of pollution than those once labeled “desirable,” the study found. This was true for all sizes of particles. The spatial disparities were largest, however, in Seattle neighborhoods that received no label because they were once considered industrial areas.��

In those previously industrial areas, ultrafine particle concentrations were 49% above average.����

“These results are important because air pollution exposure has been shown to lead to detrimental health effects, and these health effects disproportionately impact racialized and low-income communities,” said , the study’s lead author, who graduated from the 91���� in 2022 with a degree in industrial and systems engineering. “Notably, air pollution is just one factor, and there are plenty of other examples of how systemic racism is detrimental to people’s health and well-being.”��

Bramble said the results didn’t surprise her. She was raised in Tacoma, in a neighborhood near Interstate 5, where the constant crush of cars and diesel trucks spewed pollution into the air. And as a student journalist at the 91����, she researched the relationship between redlining, green spaces, heat and air pollution.����

“In the case of air pollution exposures, these policies affect the health of real people. I think at a time where the teaching of systemic racism is a controversial topic in this country, being ignorant is not going to reduce the number of children who suffer from asthma due to air pollution,” Bramble said. “Instead, I hope we can have conversations about how past policies affect us today, to drive efforts toward a healthier, sustainable society.”��

Bramble proposed and carried out this study for the grant program, which provides National Institute of Environmental Health Sciences funding and mentorship to undergraduates from underrepresented backgrounds to pursue research. She joined the program in June 2020 under Sheppard’s mentorship.����

Other 91���� authors are Magali Blanco, Annie Doubleday and Amanda Gassett of the Department of Environmental and Occupational Health Sciences, Anjum Hajat of the Department of Epidemiology and Julian Marshall of the Department of Civil and Environmental Engineering.����

For more information, contact Sheppard at sheppard@uw.edu.��

Most conscientious adults tend to avoid making biased or discriminatory comments in the presence of children.

But new from the 91���� suggests that preschool-aged children can learn bias even through nonverbal signals displayed by adults, such as a condescending tone of voice or a disapproving look. Published Dec. 21 in the journal Psychological Science, the research found that children can “catch” social bias by seeing negative signals expressed by adults and are likely to generalize that learned bias to others.

“This research shows that kids are learning bias from the non-verbal signals that they’re exposed to, and that this could be a mechanism for the creation of racial bias and other biases that we have in our society,” said lead author , a postdoctoral researcher in the 91����’s Institute for Learning & Brain Sciences.

“Kids are picking up on more than we think they are, and you don’t have to tell them that one group is better than another group for them to be getting that message from how we act.”

The research involved an initial group of 67 children ages 4 and 5, an equal mix of boys and girls. The children were shown a video in which two different female actors displayed positive signals to one woman and negative signals to another woman. All people in the video were the same race, to avoid the possibility of racial bias factoring into the results.

The actors greeted both women the same way and did the same activities with both (for example, giving each a toy) but the actors’ nonverbal signals differed when interacting with one woman��versus the other. The actor spoke to one woman��in a positive way — smiling, leaning toward her, using a warm tone of voice — and the other negatively, by scowling, leaning away and speaking in a cold tone. The children were then asked a series of questions — such as who they liked the best and who they wanted to share a toy with — intended to gauge whether they favored the recipient of positive nonverbal signals over the recipient of negative nonverbal signals.

The results showed a consistent pattern of children favoring the recipient of positive nonverbal signals. Overall, 67 percent of children favored the recipient of positive nonverbal signals over the other woman — suggesting they were influenced by the bias shown by the actor.

The researchers also wondered if nonverbal signals could lead to group bias or prejudice. To get at that question, they recruited an additional 81 children ages 4 and 5. The children were shown the same videos from the previous study, then a researcher introduced them to the “best friends” of the people in the video. The “friends” were described as members of the same group, with each wearing the same color shirt as their friend. The children were then asked questions to assess whether they favored one friend over the other.

Strikingly, the results showed that children favored the friend of the recipient of positive nonverbal signals over the friend of the other woman. Taken together, the researchers say, the results suggest that biases extend beyond individuals to members of groups they are associated with.

Skinner pointed out that many American preschoolers live in fairly homogenous environments, with limited ability to witness positive interactions with people from diverse populations. So even brief exposure to biased nonverbal signals, she said, could result in them developing generalized biases. The simulations created for the study represent just a small sample of what children likely witness in real life, Skinner said.

“Children are likely exposed to nonverbal biases demonstrated by multiple people toward many different members of a target group,” she said. “It is quite telling that brief exposure to biased nonverbal signals was able to create a bias among children in the lab.”

The study’s findings, she said, underscore the need for parents and other adults to be aware of the messages — verbal or otherwise — that they convey to children about how they feel about other people.

Co-authors are , co-director of the 91���� Institute for Learning & Brain Sciences, and , a 91���� assistant professor of psychology. Funding for the research was provided by the��91���� Ready Mind Project��Innovative Research Fund.

For more information, contact Skinner at 206-685-1310 or skinna2@uw.edu.

A 2012 by the Pew Research Center found that interracial marriages in the U.S. had doubled between 1980 and 2010 to about 15 percent, and just 11 percent of respondents disapproved of interracial marriage.

But new from the 91���� suggests that reported acceptance of interracial marriage masks deeper feelings of discomfort — even disgust — that some feel about mixed-race couples. Published online in July in the Journal of Experimental Social Psychology and co-authored by 91���� postdoctoral researcher , the study found that bias against interracial couples is associated with disgust that in turn leads interracial couples to be dehumanized.

Lead author , a 91���� postdoctoral researcher, said she undertook the study after noting a lack of in-depth research on bias toward interracial couples.

“I felt like the polls weren’t telling the whole story,” said Skinner, a researcher in the 91����’s .

The research involved three experiments. In the first, 152 college students were asked a series of questions about relationships, including how disgusted they felt about various configurations of interracial relationships and about their own willingness to have an interracial romance. The participants overall showed high levels of acceptance and low levels of disgust about interracial relationships, and pointed to a strong negative correlation between the two.

In the second experiment, the researchers showed 19 undergraduate students wedding and engagement photos of 200 interracial and same-race couples while recording their neural activity. The researchers asked the students to quickly indicate whether each couple should be included in a future study on relationships, a task that was intended to ensure participants were socially evaluating the couples while their neural activity was recorded.

Participants responded faster to images of same-race couples and selected them more often for inclusion in the study. More significantly, Skinner said, participants showed higher levels of activation in the — an area of the brain routinely implicated in the perception and experience of disgust — while viewing images of interracial couples.

“That indicates that viewing images of interracial couples evokes disgust at a neural level,” Skinner said.

As with all neuroscience studies, Skinner said, it is impossible to be certain whether the insula activation reflected a disgust response, since the insula is sometimes responsive to other emotions. But in combination with the other experiments, the authors believe it is evidence of a neural disgust response.

Lastly, the researchers used an , used to measure attitudes and beliefs people may be unwilling to acknowledge, to gauge whether feeling disgusted would impact more than 200 participants’ feelings about interracial couples. One group was first shown a series of disgusting images (a dirty toilet, a person vomiting), while the other was shown pleasant images of cityscapes and nature.

During the implicit association test, the two groups were tasked with categorizing photographs of same-race and interracial couples and silhouettes of humans and animals. They were first instructed to press one computer key if the image showed an animal silhouette or a mixed-race couple, and another key if it was a human silhouette or a same-race couple. Then the combinations were switched — participants were told to hit one key if the image was an animal silhouette or a same-race couple, and the other key if it was a human silhouette or mixed-race couple.

Participants were quicker to associate interracial couples with non-human animals and same-race couples with humans. That suggests that interracial couples are more likely to be dehumanized than same-race couples, the researchers write, and previous studies have shown that people tend to exhibit more antisocial behavior and are more likely to use aggression and even violence toward dehumanized targets.

Taken together, the experiments show that despite high levels of reported acceptance, bias against mixed-race couples persists in the United States, the researchers say. In 2013, they note, Washington Post columnist Richard Cohen caused a furor when he that New York Mayor Bill de Blasio’s interracial marriage incited “a gag reflex” among some people, prompting the Post to write a follow-up about the controversy.

Such sentiments, Skinner said, belie the notion that most Americans are ready to embrace mixed-race romance.

“Some people are still not comfortable with interracial relationships, or at least they’re a lot less comfortable than they would appear to be,” she said. “Acknowledging these biases is the first step to figuring out why people feel that way and determining what can be done so they won’t.”

For more information, contact Skinner at 206-685-1310 or skinna2@uw.edu.

Female college students are more likely to abandon studies in science, technology, engineering and math (STEM) disciplines than their male classmates, and new research from the 91���� suggests that those male peers may play a key role in undermining their confidence.

Published this week in the journal PLOS ONE, found that males enrolled in undergraduate biology classes consistently ranked their male classmates as more knowledgeable about course content, even over better-performing female students.

The over-ranking equated to males ranking their male peers smarter by three-quarters of a GPA point than their equally-performing female classmates, showing what researchers say amounts to a clear and consistent gender bias. Female students, on the other hand, repeatedly showed no significant bias in whom they picked as knowledgeable.

“This shows that there is a huge inequity in who male students think is strong in the class materials,” said lead author , a doctoral candidate in the 91���� Department of Anthropology.

“Males were consistently nominated as being more knowledgeable by their male peers, regardless of performance.”

The study involved surveying around 1,700 91���� students enrolled in the same undergraduate biology course. Students in three classes were asked to name the classmates they considered strongest in their understanding of class materials at multiple points in the course. Additionally, instructors were surveyed on which students were most outspoken in class — an effort to determine which students would be most visible to other students as knowledgeable, given the large class size. More males than females were considered outspoken by the instructors, the researchers found.

Even after accounting for differences in performance and outspokenness, male students got more recognition from other males than their female peers did, and the finding was consistent across 11 different class surveys. For an outspoken female student to be nominated by males at the same level as a male student, her performance would need to be more than three-quarters of a GPA point higher than the males.

“Using 91����’s standard grade scale, that’s like believing a male with a B and a female with an A have the same ability,” said co-lead author , who participated in the research as a 91���� postdoctoral biology researcher and is now a research scientist at the University of Texas, Austin.

On the other hand, females nominated their male and female peers almost equitably across all the surveys, after controlling for differences in performance and outspokenness. The researchers determined that the female bias was so small it could have arisen by chance, and they estimate that gender bias among male students was 19 times stronger than among females. The top three most-nominated students in all classes were male, even though there were also outspoken female students in the class with the same grades.

The findings are troubling, said Eddy, since peer support is a key factor in retaining women in STEM fields.

“To stay in STEM you have to believe you can do it, and one of the things that can convince you of that is your peers saying you can do it,” she said.

“Helping students find peers who believe in them is really important, especially for women, because they’re not likely to get that from males in their class.”

The paper grew from research Eddy and other 91���� biology colleagues were doing on gender disparities in biology education. A previous by the group found male students entering biology with the same GPA level as their female peers performed better in introductory biology. They also found that female students generally felt speaking up in class.

Grunspan, meanwhile, was doing research on how undergraduates form study networks. He initially wasn’t focused on the gender makeup of those networks, but noticed a pattern of male students viewing their male peers as being stronger in course materials. As he dug further into the data, that pattern became even more pronounced.

“I realized that there was a really big problem,” Grunspan said. “Something is going on in the classroom that is either being influenced by currently held implicit biases or that is helping build implicit biases. We need to be thinking about what that means for the future.

“Students are the future policymakers in the country,” he said. “They are the people who will someday be responsible for hiring and making other important decisions. Because these are millennials showing this pattern, it means the age-old problem of gender bias may not go away simply because we have a new generation in charge.”

Previous research has focused on gender biases among faculty in STEM disciplines, but less is known about how current college students perceive women in STEM and how their views might impact female students. The researchers focused on biology, since females and males enroll equally in biology courses at the undergraduate level. The gender bias their study revealed, they say, could be even more pronounced in other STEM disciplines.

“Given that we typically think of biology as a STEM field without a gender gap, you could imagine that other fields like physics or mathematics or engineering, which numerically are very dominated by males, would have an even stronger effect than what we’re finding,” Eddy said.

The researchers say gender bias in the classroom could be mitigated through simple measures such as fostering female study groups, using randomized class lists to call on students to participate and creating small-group discussions to establish a less intimidating environment for women.

But changing systemic gender biases, Eddy acknowledged, is a difficult challenge. The study’s authors and their colleagues are addressing that challenge through ongoing research that they hope will help inform inclusive teaching practices.

“As science instructors at the college level, you can only affect so much,” she said. “There’s been at least 18 years of socialization. You do what you can to interrupt that.”

Other co-authors are , an assistant professor of biology at Arizona State University, Tempe; , an instructional coordinator in the 91���� Department of Biology; , a member of the 91���� Biology Education Research Group; and , a 91���� associate professor of anthropology.

“We can produce discrimination without having any intent to discriminate or any dislike for those who end up being disadvantaged by our behavior,” said 91���� psychologist , who co-authored the review with of the University of California, Santa Cruz.

Greenwald and Pettigrew reviewed experiments and survey methods from published scientific research on discrimination from the last five decades. They were surprised to find that the discrimination observed in those studies occurred much more often as helping rather than harming someone. But they also found that most researchers defined discrimination as based on negative attitudes and hostility, only rarely treating favoritism as a component of discrimination.

That makes sense, Greenwald said, because most people think of discrimination as the result of hostility: a white person spouting anti-black rhetoric, or a homophobe yelling slurs at a gay couple. But, he argues, it’s more subtle acts, ones people don’t even recognize as causing disadvantage to anyone, that are likely to be much more significant.

Take this hypothetical scenario: When conducting reviews of two employees, a manager finds they both fall between two performance categories. The manager gives a higher category to the employee whose child is friends with the manager’s child, leading to a promotion and salary raise, while the other employee receives a smaller raise and no promotion.

Was the manager consciously discriminating against the second employee? Or did she simply give a boost to someone to whom she had an “ingroup” connection?

“Your ‘ingroup’ involves people that you feel comfortable with, people you identify with,” Greenwald explained. “We usually think first of demographic characteristics like age, race, sex, religion and ethnicity as establishing an ingroup, but there are also ingroups based on occupation, neighborhood and schools attended, among other things. Outgroups are those with whom you don’t identify.”

Greenwald and Pettigrew propose that unequal treatment in the form of doing favors for those like you, rather than inflicting harm on those unlike you, causes the majority of discrimination in the U.S.

“This is not to say that prejudice and hostility are not related to outgroup discrimination,” Pettigrew said. “But they are not as central to most discrimination as ingroup favoritism.”

Yet, historically, social scientists have emphasized prejudicial hostility as the root of discrimination.

“We looked at how prejudice has been defined in the history of psychology. It has generally been understood as hostility toward outgroups. That’s easy to do, because inter-group conflict is an obvious fact of life,” Greenwald said. “There are international conflicts, wars, gang battles, labor-management conflicts. When such conflicts are going on it’s natural to think of them as rooted in hostility.”

Greenwald hopes researchers will change how they study discrimination, because research results have substantial implications both for how discrimination is identified and how it can be ameliorated in employment, health care, education and daily life.

He said overt acts of discrimination began to decline starting in the 1960s following civil rights laws. But prejudicial attitudes didn’t necessarily change. What changed is that people were no longer legally allowed to act on their prejudices by, for example, denying housing to blacks or jobs to women.

The co-authors say that racial ingroup favoritism can be very subtle. For instance, if you work in an office that is mostly white and you’re asked to recommend someone for a job opening, you’re more likely to recommend someone who is like you and the rest of your ingroup.

This sort of ingroup favoritism happens at all ages and in different situations. Greenwald said it can happen on the playground, where children may exhibit ingroup favoritism based on race, economic class, or the same school or sports team.

“Hostility isn’t integral to the definition of discrimination; you can treat people differently without being hostile to anyone,” Greenwald said. “But it is societally important to understand how discrimination can occur both without hostility and without any intent to discriminate.”

# # #

For more information, contact Greenwald at agg@uw.edu or 206-543-7227, or Pettigrew at pettigr@ucsc.edu or 831-425-4777.

Note to media: For a PDF of the American Psychologist article, please contact Doree Armstrong, 91���� News Office, at doreea@uw.edu or 206-543-2580.