Diesel fumes appear to combine with artery-clogging fats to raise the risk of heart disease, research suggests.
Scientists found the two act in concert to switch on genes that cause potentially dangerous inflammation of the blood vessels.
They hope their work will lead to a simple blood test enabling doctors to evaluate the impact of air pollution on a person's health.
The UCLA study appears in the online journal Genome Biology. Lead researcher Dr André Nel, an expert in nanomedicine, said the impact of diesel particles and cholesterol fats combined was much greater than the impact of each in isolation.
He said: "Their combination creates a dangerous synergy that wreaks cardiovascular havoc far beyond what's caused by the diesel or cholesterol alone."
The researchers focused on the interaction between diesel exhaust particles and fatty acids found in low-density lipoprotein (LDL) cholesterol - the "bad" type of cholesterol that leads to artery blockage.
Both are sources of molecules called free radicals which cause cell and tissue damage, and can trigger the inflammation that leads to artery disease.
Source - BBC