But at that point it still wasn't clear whether those findings held for office workers too. Desk work is both indoors and far less physically strenuous than packing fruits and vegetables in a warehouse, so one might reasonably conclude that white collar workers are less vulnerable to the effects of air pollution simply because they're not breathing in as much air.
But that's not the case, as the latest study concludes. For the paper, Steffen Meyer and Michaela Pagel took data on stock trades made by over 100,000 private investors in Germany from 2003 to 2015, and paired it with data on air quality, weather and traffic from the closest of over 1,600 monitoring stations.
Why stock trades? “We interpret individual investor trading, an indoor activity that requires some skill and cognitive but no physical exertion, as a proxy for willingness and ability to engage in office work and thereby white-collar productivity,” Meyer and Pagel explain. The stock data is particularly useful because it allowed the researchers to measure human behavior at the individual level.
Outdoor air quality can fluctuate significantly from day-to-day. Meyer and Pagel wanted to know if these fluctuations had any effect on individual investors' propensity to log in and make a trade on a given day.
To isolate the effect of air pollution, they'd first need to control for a whole host of other factors known to affect trading behavior: day of the week (markets aren't open every day), day of the year (markets are busier at certain times of year), preceding market returns, changes to daylight saving time, weather and traffic.
With those other factors accounted for, Meyer and Pagel focused on the effect of particulate matter in the air, a measure known as PM10 — particles about 1/7th the thickness of a human hair, small enough to be inhaled deep into the lungs. These particles come from vehicle exhaust, construction dust, industrial sources, wood burning and other sources, and are linked to everything from asthma to general respiratory distress to heart attacks and even death.
They found that a modest increase in outdoor PM10 — 12 micrograms of the pollutant per cubic meter — reduced investors' propensity to trade by nearly 10 percent. They characterize that effect as “large and significant,” akin to the decrease in trading observed on a nice sunny day versus a cloudy one.
It's worth pointing out that a 12 microgram increase in PM10 is not a whole lot — on any given day in Germany, levels of the pollutant usually fluctuate between 0 and 40 micrograms, and often more than that.
“To the best of our knowledge, this paper is the first to test whether air quality affects investor willingness to sit down and trade, controlling for investor-, environment- and market-specific factors in a commonly found low-pollution environment,” the authors conclude. “The negative effects of pollution on white-collar work productivity are much more severe than previously thought.”
The finding comes at a time when federal authorities in the United States are working to undo certain air quality regulations. In particular, a number of President Trump's appointees to the Environmental Protection Agency have raised eyebrows for rejecting the broad scientific consensus on the effects of air pollution.
The University of California at Irvine's Robert Phalen, for instance, believes that “modern air is a little too clean for optimum health.” Michael Honeycutt, the new chairman of the EPA's Science Advisory Board, has written that federal regulations on ozone are unnecessary because “most people spend more than 90 percent of their time indoors.”
And as the research out of Germany shows, air pollution outdoors can have a significant impact on your ability to do your indoor job.