Long-term exposure to traffic-related pollution may significantly increase the risk of asthma in early childhood, a study has warned.The findings, published in the Journal of Allergy and Clinical Immunology, showed that living close to a major road was linked to childhood asthma at all ages examined."Children living less than 100 metres from a major road had nearly three times the odds of current asthma - children who either experience asthma symptoms or use asthma medications daily - by ages seven to 10, compared with children living more than 400 metres away from a major road," said study co-author Mary Rice from the Beth Israel Deaconess Medical Center (BIDMC) in Boston, US.For the study, the researchers analysed data from 1,522 Boston-area children born between 1999 and 2002.The researchers used mapping technologies to determine the distance between each child's home address and the nearest major roadway. They also linked home addresses to census data and satellite-derived atmospheric data to calculate each participant's daily exposure to fine particulate matter (PM) -- tiny particles suspended in the air that when inhaled deposit in the terminal sacs of the lung. Fine PM originates from fuel combustion, including traffic, power plants, and other pollution sources, the researcher said.The research team also examined children's daily exposure to soot, a component of fine PM also known as black carbon.The researchers found that traffic-related pollutants appeared to increase asthma risk in childhood."Lifetime exposure to black carbon and fine PM were also linked to the asthma in early childhood (ages three to five years), but in mid-childhood (ages seven to 10 years), these pollutants were associated with asthma only among girls," the researcher noted.