There's a profound truth to one of the mottoes of protesters in New York who are upset about a grand jury's decision not to indict an officer in the death of Eric Garner on Staten Island this summer. "We can't breathe," they have been chanting. And in New York, as in most American cities, the air itself has been tainted by decades of disparity in public policy.

The motto paraphrases Garner's words as Officer Daniel Pantaleo held him in an apparent chokehold on the sidewalk. Pantaleo told the grand jury he did not intend to choke Garner and tried to let go of him when Garner said, "I can't breathe," but the asthmatic Garner suffered a heart attack and died several minutes later in the back of ambulance. A medical examiner ruled the death a homicide.

We'll never know if Garner would have survived the altercation if he hadn't had asthma. We also don't know what caused the asthma, which he developed as a child. What we do know is that asthma is much more common among blacks than whites, and that air pollution is much worse in communities of color nationwide.

Asthma was one among many factors correlated with race in Garner's life that led to the fatal situation, said Eddie Bautista, director of the New York City Environmental Justice Alliance. "There are number of ways that racism plays out," he said. "The asthma is just one more example."

A recent study found that members of racial and ethnic minorities are exposed to levels of nitrogen dioxide, a common pollutant associated with asthma and heart disease, that are 38 percent higher than in the air whites breathe.

Advocates say that authorities often decide to dump waste in minority neighborhoods, and to locate highways and industrial facilities away from the higher-income areas where whites live.

Garner lived in Tompkinsville, a neighborhood on Staten Island's north shore where zoning regulations have concentrated shipping and industry, Bautista said.

The north shore of the island is one of six areas that New York City has designated for marine freight. Bautista's group analyzed the demographics of these zones and found that about two-thirds of the people living in them were not white.

Historically, he said, immigrants and people of color moved to these waterfront neighborhoods because they could live and find work there despite a lack of money and qualifications.

More recently, as the city has converted industrial land elsewhere into gentrifying residential and commercial neighborhoods, industry has further concentrated in the waterfront districts, likely leading to more asthma-causing pollutants.

"The more industrial land you take off the table, the less land you have, the greater the potential for clustering. It's a vicious cycle," Bautista said.

In one neighborhood, Hunts Point and Mott Haven in the Bronx, the rate at which children are hospitalized for asthma is about twice the city's average.

Pollution is not the only cause of asthma. Psychological factors play a role as well, including anxiety, stress and exposure to violence.

Children who live in neighborhoods where crime is high have been shown to have higher rates of asthma. For people living in old, poorly maintained houses, exposure to cockroaches is another risk: the insects produce allergens that might cause asthma in children.