Air pollution is a universal problem in industrialized nations, and particulates typically found in air pollution have been implicated in chronic diseases. Robert D. Brook, from University of Michigan (USA), and colleagues tested 83 people as they breathed levels of air pollution similar to those in an urban city near a roadway.  The air pollution caused diastolic pressure (the second number in a blood pressure reading) to rise within two hours.  Further, blood vessels were impaired for as long as 24 hours.  Testing showed that particulates in the air, rather than ozone gases, caused the rise in blood pressure and impaired blood vessel function.  Dr. Brook observes that: While the diastolic pressure increase may not be problematic for healthy people, "this small increase may actually be able to a trigger a heart attack or stroke” in compromised or older individuals.   He recommends that: "If air pollution levels are forecasted to be high, those with heart disease, diabetes, or lung disease should avoid unnecessary outdoor activity.”