31.   Van de Brooke said the samples may have detected normal background levels from car exhaust.

32.   Analysts say most of the pollution comes from car exhaust.

33.   During the hot summer months, air pollution in the mountain-ringed Athens basin often soars beyond danger levels and car exhausts are mostly to blame.

34.   Environmentalist say the elevated system will trap car exhaust.

35.   Natural gas vehicles cut toxic car exhaust as well as carbon dioxide emissions, compared to regular gasoline and diesel engines.

36.   Nitrogen dioxide, which is mainly emitted by car exhausts, hovered close to warning levels in central Athens, the environment ministry said.

37.   Some environmentalists say the elevated system will trap car exhaust.

38.   The converters, while breaking down smog-causing nitrogen and oxygen from car exhaust, are also rearranging the compounds to form nitrous oxide.

39.   The main pollutant is nitrogen oxide from coal-burning and car exhaust, the reports said.

40.   The other main source is air pollution from car exhaust, industrial exhaust and burning garbage.