Kids who live around heavy traffic pollution have lower IQs and score worse on other tests of intelligence and memory than children who breathe cleaner air, according to a new study.

According to Reuters Health, the new study says the effect of pollution on intelligence was similar to that seen in children whose mothers smoked 10 cigarettes a day while pregnant, or in kids who have been exposed to lead.

Dr. Shakira Franco Suglia of the Harvard School of Public Health in Boston and her team said that while the effect of pollution on cardiovascular and respiratory health has been studied extensively, less is known about how breathing dirty air might affect the brain, Reuters said.

Suglia and her colleagues studied 202 Boston children 8 to 11 years old who were participating in a study of maternal smoking. The researchers related several measures of cognitive function to the children’s estimated exposure to black carbon, a component of the particulate matter emitted in automobile and truck exhaust, particularly by diesel vehicles.

The more heavily exposed children were to black carbon, the lower were their scores on several intelligence tests.

When the researchers adjusted for the effects of parents’ education, language spoken at home, birth weight, and exposure to tobacco smoke, the association remained, Reuters said.

For example, heavy exposure to black carbon was linked to a 3.4-point drop in IQ, on average. Heavily exposed children also scored lower on tests of vocabulary, memory and learning.

“It’s within the range for in utero tobacco exposure and lead exposure,” Suglia told Reuters.

Suglia also said that exposure to traffic pollution has been associated with a number of other harmful effects and that, short of moving away from heavy traffic areas, there’s not much people can do to limit it.