Polycyclic aromatic hydrocarbons (PAHs) are pollutants released into the air from the burning of coal, diesel, oil and gas. Researchers from the Mailman School of Public Health at Columbia University in New York looked into the effect of PAHs on the IQs of children who had been exposed to them in the womb. They studied 249 children born to Black and Dominican-American women aged between 18 and 35. The women wore personal air monitors to measure their exposure to PAHs during their pregnancy and the children's IQs were measured when they were five. The study found that children exposed to high levels of PAHs while they were in the womb had IQs around 4.5 points lower than those who had been less exposed to the chemicals.