1.   In addition, diesels generally require less maintenance than petrol engines and can retain impressive emission levels over large mileages.

2.   In most cases, emission levels were orders of magnitude below standard recommended levels.

3.   They called for high power and torque, low smoke and exhaust emission levels, quiet, and good fuel economy.

4.   And the additional power comes with lower emission levels and more fuel efficiency.

5.   As a result, air emission levels tend to be highest in downtowns and other areas where congestion occurs.

6.   A new round of extremely stringent government exhaust emissions levels is coming up, requiring major expenditures in research and new tooling.

7.   Businesses are given emission levels and told how to reach their reduction goals and what equipment to buy.

8.   But the major manufacturers agreed with the EPA on a system under which they will reduce average emission levels sharply.

9.   Federal regulations permit a company that cuts pollution below federal levels to sell credits it has earned to a company unable or unwilling to meet those federal emission levels.

10.   For many years, SUVs and light trucks were considered work vehicles, and their heavier engines were allowed to meet less stringent emissions levels than passenger cars.