The article “Exhaust Emissions from Four-Stroke Lawn Mower Engines” (J. of the Air and W...

The article “Exhaust Emissions from Four-Stroke Lawn Mower Engines” (J. of the Air and Water Mgmnt. Assoc., 1997: 945–952) reported data from a study in which both a baseline gasoline mixture and a reformulated gasoline were used. Consider the following observations on age (yr) and NO_x emissions (g/kWh):

Construct scatter plots of NO_x emissions versus age. What appears to be the nature of the relationship between these two variables? [Note: The authors of the cited article commented on the relationship.]