In a study of nitrogen dioxide (N02) pollution within vehicles, three models of cars were driven for 1 hr in a town area (A) and an adjacent country area (B). Triethanolamine disc was installed in each car to record the mean nitrogen dioxide concentration over the 1 hr period. Nitrogen dioxide (ppb) Vehicle model Area A Area B 1 17.4 12.3 1 11.8 18.2 1 12.5 19.0 2 32.3 21.8 2 38.1 41.0 2 34.2 38.6 3 21.6 16.4 3 36.0 19.8 3 23.0 15.7