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 [the link may be paywalled]. From a report: 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.
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