1.   Because many diesel trucks travel across state lines and are registered outside Arizona, they are harder to regulate than gasoline-powered vehicles.

2.   Huge, ancient diesel trucks lumbered through the crowd between tractors and horse-drawn carts.

3.   As the diesel truck approached, I flagged the driver to stop.

4.   But diesel trucks have not been subjected to the same stringent requirements, in part because of the costs.

5.   But Whitman also angered the oil and trucking industries when she upheld a Clinton rule demanding cleaner diesel trucks and buses.

6.   Fumes from diesel trucks are important contributors to smog, which plagues New York City, and acid rain, which damages lakes and forests in the Adirondacks.

7.   In addition, nitrogen oxide from diesel trucks and buses is also a prime ingredient in smog, which has been linked with respiratory illnesses.

8.   It also was among the first to use diesel trucks.

9.   Smog and particulate matter, especially from diesel trucks and buses, remain problems.