In 2011 researchers at UC San Diego and Columbia University were the first to demonstrate a link between air pollution and reduced productivity among outdoor agricultural workers. Now those researchers are back with a new study, entitled “Particulate Pollution and the Productivity of Pear Packers.” The study shows, for the first time, a significant link between air pollution and the productivity of indoor workers.

The pollutant in question is fine particulate matter, or PM 2.5 . It’s notable for its tiny size (less than 1/30th the width of a human hair), which allows it to infiltrate deep into your lungs and potentially even your bloodstream, where it can cause all sorts of health problems. The authors note that PM 2.5 can easily enter buildings: “Unlike other pollutants, which either remain outside or rapidly break down once indoors, going inside may do little to reduce one’s exposure to PM 2.5 .”

To figure out how this affected indoor workers, the authors drew on data from an indoor pear-packing factory in northern California. “We focused on pear packing for this study since it was located near an air pollution monitor and paid workers piece rate, which allowed us to measure individual worker productivity on a daily level,” author Joshua Graff Zivin told me.

What they found was that every 10-microgram per cubic meter increase in PM 2.5 levels decreased worker productivity by 0.6%, as measured by the number pear boxes packed by each worker. Since workers were paid piecemeal, this translated to a decrease of roughly 41 cents per hour, per 10 micrograms of PM 2.5 .

Moreover, the effect increased at higher PM 2.5 levels: levels between 15 and 20 micrograms reduced earnings by $0.53 per hour, levels between 20 and 25 micrograms decrease earnings by $1.03 per hour, and when levels exceed 25 micrograms/cubic meter earnings shrink by $1.88 per hour. One key point is that these levels are all well below current U.S. air quality standards for PM 2.5 , which stand at 35 micrograms/m3. The U.S. didn’t even start regulating this pollutant until 1997.

Across the U.S., PM 2.5 levels routinely cross this 35 microgram threshold every day. Airnow.gov, an EPA website that tracks air quality in U.S. cities, is currently showing PM 2.5 levels of 69 micrograms in Atlanta, 72 in Cleveland, and a whopping 140 in Albuquerque, NM. If those figures seem high be thankful you don’t live in Beijing, where PM 2.5 levels topped 250 micrograms today.

One major implication of the study is that reductions of PM 2.5 can have significant economic benefits. The authors estimate that across the entire U.S. manufacturing sector, reductions in PM 2.5 since 1997 has led to an aggregate labor savings of $19.5 billion – a previously-unknown benefit of fine particulate regulation.

The larger question, of course, is whether these findings extend even to workers in retail and other regular office settings. “We are very curious about this,” Graff Zivin told me. “Whether more cognitive indoor activities are subject to similar effects is an important area for future research, but there is certainly a plausible channel through which these could occur.”