Urban ecologists say it is difficult to measure the ecological impacts of cities, but they are working on a way to quantify the number of humans who live there.
That is the focus of the first National Urban Ecological Footprint Survey.
In the study released Wednesday, researchers estimate that there are more than 100 million people in the U.S. who live in cities.
About 40 percent of them live in areas where the population exceeds 1 million.
The researchers looked at how many of those people were exposed to the pollutants that are contributing to climate change and other environmental problems.
The survey will be the first large-scale urban ecology survey, using a wide range of data sources to estimate the impact of cities on the health of their people.
The study will be presented at the annual meeting of the American Association for the Advancement of Science in Orlando, Florida.
The report, released by the National Urban Ecology Association, found that a third of the cities studied had pollution levels greater than 100 micrograms per cubic meter, the U,S.
Environmental Protection Agency defines as the smallest detectable amount of a pollutant in a given cubic meter of air.
A third of these cities had concentrations of PM10, a particle with a 10-nanometer diameter that is dangerous to breathe, greater than the EPA limit of 10 microgram per cubic foot.
The average concentration of PM2.5, the second largest pollutant, was 10 microg per cubic inch.
The results show that cities that have more people have more pollution, said James Glynn, a professor of urban and regional planning at Arizona State University.
That’s because more people are moving into these cities, and so they are more susceptible to pollutants.
The research team looked at data from the EPA’s National Ambient Air Quality Index, a database that records pollution from sources such as cars, buildings, trucks and power plants.
They compared the data to the EPA data and found that cities with more people had more pollutants.
These cities include New York, Los Angeles, San Francisco and Washington, D.C. In addition to PM10 and PM2, the researchers found pollutants like carbon monoxide and benzene in more than half of the areas.
It is also important to look at pollution that doesn’t cause symptoms, said Michael Shaffer, a senior scientist at the Urban Ecology Center at the University of Michigan who was not involved in the study.
It’s not the type of pollution that causes the symptoms, he said.
Cities are also contributing to CO 2 emissions that are a major contributor to climate warming, he added.
He said that in addition to CO2, there are other pollutants that contribute to climate changes, such as nitrous oxide and sulfur dioxide.
The polluters include the chemicals used in factories, the construction industry, and agricultural and forestry activities.
It also takes into account the number and type of people living in the areas that are exposed to pollutants, said Shaffer.
Some cities are having a positive effect on health, but others are causing health problems, he noted.
The EPA will update the national survey to reflect the data from more cities over time.
Shaffer said he believes the report will help inform public policy makers about the impacts of the urban environment.
The National Urban Ecosystems Survey was funded by the U of M’s Institute for Urban Ecology.
For more information on the National Environmental Science Program, visit nsep.umich.edu.