High levels of traffic exhaust even at one's residence increases the risk of stroke according to a study published in the journal Environmental Health Perspectives. Researchers in the study suggested that it is mainly black carbon from traffic exhaust responsible for causing stroke and not particulate matter emanating from other sources. Black carbon is the sooty black material emitted from gas and diesel engines coal-fired power plants and other fuels. In city environments emissions come mainly from road traffic. These particles have previously been linked to negative health effects especially in studies of heavily polluted environments. Researchers at Karolinska Institutet