People exposed to fine-particulate air pollution caused primarily by vehicle exhausts, coal-fired power plants and other industrial sources could face the risk of developing heart disease, says a study.

The study by Joel Kaufman of the University of Washington and other researchers found that air pollution is a much bigger factor in deaths from heart ailments or strokes than has previously been recognised, reported an online edition of health magazine WebMD.

Researchers followed 66,000 women - aged 50-79 - living in 36 cities. All the women were enrolled in an ongoing health study, the Women's Health Initiative.

After adjusting for other risk factors for heart disease and stroke, the researchers in their study said that each 10-unit increase in air levels of fine particulate matter was associated with a 76 percent increase in the risk of death from cardiovascular disease.

Particulate matter is the general term used for a mixture of solid particles and liquid droplets in the air. It includes aerosols, smoke, fumes, dust, ash and pollen.

The composition of particulate matter varies with place, season and weather conditions. Fine particulate matter is 2.5 microns in diameter and less.

It is also known as PM2.5 or 'respirable' particles because it penetrates the respiratory system further than larger particles.

Earlier scientific studies have linked particulate matter, especially fine particles, with a series of significant health problems, including premature death, respiratory disorder, chronic bronchitis and decreased lung function.