ATHLETES DON’T get advance warning of drug tests. Police don’t share schedules of planned raids. Yet America’s Environmental Protection Agency (EPA) does not seem convinced of the value of surprise in deterring bad behaviour. Every year it publishes a list of dates, spaced at six-day intervals, on which it will require state and local agencies to provide data on concentrations of harmful fine particulate matter (PM2.5), such as soot or cement dust.
In theory, such a policy should enable polluters to spew as much filth into the air as they like 83% of the time, and clean up their act every sixth day. However, this ill-advised approach does offer one silver lining: it lets economists measure how much businesses change their behaviour when the proverbial parents are out of town.
A new paper by Eric Zou of the University of Oregon makes use of satellite images to spy on polluters at times when they think no one is watching. NASA, America’s space agency, publishes data on the concentration of aerosol particles—ranging from natural dust to man-made toxins—all around the world, as seen from space. For every day in 2001-13, Mr Zou compiled these readings in the vicinity of each of America’s 1,200 air-monitoring sites.
Although some stations provided data continuously, 30-50% of them sent reports only once every six days. For these sites, Mr Zou studied how aerosol levels varied based on whether data would be reported.
Sure enough, the air was consistently cleaner in these areas on monitoring days than it was the rest of the time, by a margin of 1.6%. Reporting schedules were almost certainly the cause: in areas where stations were retired, average pollution levels on monitoring days promptly rose to match the readings on non-monitoring days.
The size of this “pollution gap” differed by region. It was biggest in parts of Appalachia and the Midwest with lots of mining, and in the northern Mountain West, where paper and lumber mills are common.
The magnitude of the gap also depended on the cost of being caught. Every year, the EPA produces a list of counties whose average air quality falls below minimum standards. The punishments for inclusion are costly: factories become subject to burdensome clean-technology requirements, and local governments can be fined.
When firms risked facing sanctions, they seemed to game the system more aggressively. In counties that exceeded the PM2.5 limit in a given month, the pollution gap in the following month swelled to 7%. In all other cases, it was just 1.2%.
The end of the one-in-six schedule is in sight. Thanks in part to a cash-incentive scheme for continuous-measurement systems, just 10% of stations now report every sixth day. However, PM2.5 are so dangerous that even this small share causes severe harm. If switching these stations to continuous reporting were to cause pollution on non-monitoring days to fall to the level seen on monitoring days, it would yield a 1.3% reduction in PM2.5 exposure for 10% of America’s population. Using a standard academic estimate of the impact of such particles on life expectancy, this amounts to just over one extra day of life per affected resident, for a total of 105,000 life-years. ■
Source: “Unwatched pollution: the effect of intermittent monitoring on air quality”, by Eric Yongchen Zou, 2021
This article appeared in the Graphic detail section of the print edition under the headline “We were expecting you”