Examining Trends of Criteria Air Pollutants: Are the Effects of Governmental Intervention Transitory?

Despite its growth in other areas of economics,time series econometric methods have not beenwidespread in the area of environmental andresource economics. We illustrate one use oftime series methods by examining the time pathof US nitrogen oxide (NO_x) emission dataover the period 1900–1994. The analysishighlights that proper time series methods canaid in optimal regulatory policy as well asdeveloping empirical verification of theoriesput forth to explain economic phenomena. Inaddition, several interesting results emerge. First, we find that the emissions seriescontains both a permanent and random component. Second, if one attributed all of the emissionsreductions to regulatory policy, interventionanalysis suggests that the 1970 Clean Air Act(CAA) did not merely have transitory effects,but permanently influenced the NO_xemission path. In terms of total regulatoryimpact, an upper bound on the emissions saveddue to the 1970 CAA is in the range of27%–48%.