Out of Africa.

M any studies from the west have implicated traffic pollution in respiratory disease, especially in children. Usually, these studies have been conducted in areas with high traffic densities such as inner cities, or areas near major highways. The daily number of vehicles passing on roads near residences or schools of study children have typically been in the tens of thousands, sometimes well over one hundred thousand. Air pollution studies conducted near such roads have shown relatively high concentrations of traffic related air pollutants, compared to sites away from the direct influence of busy roads. Typically, such contrasts were markedly larger for specific components such as NO2, soot, PAHs, and benzene than for particulate matter metrics of current regulatory interest, PM10 and PM2.5. 1 2