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  • July 19, 2021

To catch a polluter


Environmental regulators play a constant cat-and-mouse game with polluters. Federal agencies do what they can, but they don’t have the fiscal resources to perform continuous monitoring. This means that polluters have the opportunity to emit more when inspectors aren’t watching. 

In a paper that appears in the American Economic Review, author Eric Zou examines the extent to which polluters strategically respond to intermittent monitoring. Using satellite data measuring aerosol levels, Zou found that in a number of regions there were significant differences in pollution on monitored days versus unmonitored days.




Figure 7 from Zou (2021)


Figure 7 from the paper shows county-level data on “pollution gaps”—the change in pollution on days when regulators’ air quality monitors are operating versus when they aren’t. The warmer colors indicate regions with larger pollution gaps, with the largest gaps appearing in parts of California, Montana, southern Texas, and a group of states in the Midwest. The author defines “hotspot” counties (outlined in black) as those with the highest 10 percent pollution gap estimates.

The hotspot regions tend to be in areas that have  high aerosol levels and are subject to 1-in-6-day monitoring. These hotspot areas are also highly correlated with two specific industries—wood product manufacturing and mining.

Zou’s research highlights the challenges facing regulators seeking to crack down on high pollution emitters who are gaming the system.

“Unwatched Pollution: The Effect of Intermittent Monitoring on Air Quality” appears in the July 2021 issue of the American Economic Review.