This study investigates the impacts of the Automobile NOx Law of 1992 on four pollutants in Japan. By utilizing monitoring data between 1897 and 1997, we found that the regulation decreased the level of SO2 by approximately 12.4%. The improving effects on the levels of NOx, Ox, and suspended particulate matter are estimated at 5.8%, 3.1%, and 3.5%, respectively. The result from our flexible specification suggests that, although the regulated areas experienced improvements in concentration, the neighboring effects might have been negligible.
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