Older people living in cities with high levels of a particular type of air pollution are more likely to be hospitalized for heart disease, a new study reveals.

The type of air pollution in question is known as coarse particulate matter. Increased levels of this kind of air pollution have been linked to construction projects, desert winds and farming, according to the researchers.

These microscopic particles are larger than the air pollutants released by cars and power plants. Scientists say they can have a significant impact on people's health.

"We suspected that there was an association between coarse particles and health outcomes, but we didn't have the research to back that up before," said study leader Roger Peng. He is an associate professor of biostatistics at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

"This work provides the evidence, at least for cardiovascular disease outcomes. I don't feel like we need another study to convince us. Now it's time for action," Peng said in a university news release.

But, although the study found a strong link between coarse particle air pollution and heart disease hospitalizations, it wasn't designed to prove cause-and-effect.

The findings were published in the November issue of Environmental Health Perspectives.

The study involved data collected from an air-monitoring network established by the U.S. Environmental Protection Agency in 110 large urban areas. This information was linked to Medicare data on hospitalizations among people aged 65 and older in these regions between 1999 and 2010.

During the study, there were more than 6 million heart-related emergency hospital admissions and 2.5 million respiratory admissions. Respiratory diseases were not linked to high levels of coarse particles. However, admissions for heart-related emergencies were higher on days when levels of these air pollutants were elevated, the study revealed.

Where the participants lived affected hospital admission rates for heart problems. There were higher concentrations of coarse particles in the western United States, but heart-related hospitalizations were higher in the East, suggesting some particles are more harmful than others.

"Just because the particles are the same size doesn't mean they are made of the same material," Peng explained. "It's possible that the chemical composition of the particles in the east could make them more toxic."

Under the Clean Air Act, the EPA monitors finer particles, and states have taken steps to limit these pollutants with measures, such as stronger car emissions standards. Coarse particles may be more difficult to control since they often come from natural sources, the researchers noted.

How these airborne particles lead to health problems throughout the body isn't clear. The study's authors suggested a national monitoring network for these larger particles may be necessary.

"It's worth revisiting, given this new data," said Peng.