Children exposed to higher levels of air pollution during the third trimester of their mother pregnancy face a higher risk of elevated blood pressure in childhood, according to a study. Fine particulate matter of 2.5 microns or less (PM2.5) is a form of air pollution produced by motor vehicles and the burning of oil, coal and biomass, and has been shown to enter the circulatory system and negatively affect human health. Ours is one of the first studies to show breathing polluted air during pregnancy may have a direct negative influence on the cardiovascular health of the offspring during childhood,\ said Noel T Mueller, an assistant professor at the Johns Hopkins University in the US.