Researchers used satellites to measure pollution near e-commerce warehouses. The results are alarming

Online shopping is booming—e-commerce sales in the United States reached $1 trillion-plus in 2023—and to fuel that business, retailers are building more and more gigantic warehouses. As these warehouses grow, traffic increases, with delivery fleets constantly driving in and out of logistics hubs. And as traffic increases, so does pollution.

A new study shows for the first time how people living in communities downwind of large warehouses are being exposed to increased levels of pollution because of all that traffic. Neighborhoods within 5 miles of those hubs saw, on average, a nearly 20% increase in levels of nitrogen dioxide (NO2)—a pollutant regulated under the Clean Air Act that has been linked to health issues including asthma, respiratory infections, and even chronic lung disease.

Though 20% may not sound like a lot, that increase is like reversing years of improvements in air quality through regulations such as the Clean Air Act, says Gaige Kerr, lead author of the study, published recently in Nature, and an assistant research professor of environmental and occupational health at George Washington University. “Their air is not necessarily the air the rest of us are breathing,” he says of these nearby communities. “It’s kind of stuck in a more polluted past.”

Uncharted territory

The research team wanted to look at warehouse pollution after hearing concerns from environmental regulators and community members about the warehouse industry, and how it doesn’t quite have the same level of oversight as, say, power plants or factories.

Though people know traffic is associated with pollution, and communities have fought the development of new warehouses, this study is the first nationwide effort to show that people living near warehouses are exposed to higher-than-average levels of damaging pollutants. “This is kind of uncharted territory,” Kerr says. “There’s not a whole lot of work out there on warehousing and air quality.”

This is partly because the industry is still fairly new; e-commerce has ballooned in the past few decades. The warehouses of today are also different than those of years past. From 1980 to 2010, warehouses stayed around the same size. But after 2010, there was a stark increase in square footage. Between 2010 and 2021, there was a 400% increase in the median number of loading docks at new warehouses, researchers found. “Increasingly, warehouses are capable of handling more and more heavy-duty truck traffic,” Kerr says.

The other reason this pollution may have been largely overlooked relates to how it’s studied. Nitrogen dioxide dissipates pretty quickly in the atmosphere (that’s why 10 to 15 miles downwind of warehouses, the concentrations really drop). Historically, scientists relied on air pollution monitors to study air quality; there are about 500 monitors around the country that measure NO2. But because levels can vary so much from block to block, that number doesn’t capture all NO2 exposure.

For this study, researchers used satellites to measure levels of nitrogen dioxide from space—thanks to an instrument that came out around 2018. They were able to map that data with the locations of nearly 150,000 large warehouses across the country, and see a broad overview of how NO2 levels vary from neighborhood to neighborhood.

The impact of warehouse pollution

Across the U.S., communities of color are disproportionately exposed to air pollution. That proved true when it came to e-commerce warehouse pollution, too. On average, warehouses are more commonly located in communities that have more people of color, specifically Black or Hispanic residents.

And the more warehouses there are in one area, the more people of color live nearby. If there were just a couple of warehouses in a region, the demographics of nearby communities were similar to the national average. But some communities have dozens upon dozens of warehouses. San Bernardino County in California, for example, has more than 3,000 warehouses, covering almost 37 square miles.

“We found that as the number of warehouses in a given community increases, there are really dramatic, stark increases in the percentage of the population that identifies as Hispanic as well as the percent that identifies as Asian,” Kerr says—up to 290% more. (Black Americans didn’t see that same surge, though they were more represented when there were three to seven warehouses clustered together; that population was less prevalent than Asian and Hispanic populations once the clusters reached eight, nine, or ten warehouses.)

Though there are warehouses throughout the country, just 10 counties are home to 20% of these facilities: Los Angeles, San Bernardino, Orange, and Alameda, California; Dallas and Harris, Texas; Cook, Illinois; Miami-Dade, Florida; Maricopa, Arizona; and Cuyahoga, Ohio.

When it comes to the type of pollution studied, the researchers looked at nitrogen dioxide in part because it’s regulated under the Clean Air Act, and also because it’s easy to see from space. But it’s not the only pollutant associated with traffic. Heavy-duty trucks are most likely also emitting black carbon and particulate matter—pollutants that can be trickier to measure but that are also associated with a slew of health impacts, including asthma and heart attacks. Going forward, Kerr plans to look at the concentration of those other pollutants near warehouse facilities.

What to do about warehouse pollution

Some e-commerce hubs have garnered attention from regulators. In 2011, Kamala Harris, then California’s attorney general, challenged a warehouse project based on the diesel exhaust it would expose community members to. (That ended in a settlement where the developers agreed to install air quality monitoring and take pollution mitigation measures, like planting trees and putting air filters in homes.) The California Air Resources Board (for which Kerr is a consultant) has continued to look to limit warehouse pollution.

More electric heavy-duty trucks could help, too. Amazon has released a fleet of heavy-duty electric trucks across Southern California to decarbonize more than just the last mile of delivery. If that’s not appealing to companies, or isn’t technologically feasible on a larger scale, Kerr notes that policymakers could adopt more strict engine standards to make diesel trucks “cleaner.” He’d also like to see corporations taking their own steps, like by phasing out their oldest, least-efficient diesel vehicles.

The research highlights yet another environmental impact from the surge in shopping beyond the massive waste it generates. As events like Amazon Prime Day continue to sell more and more items each year, there’s impact both from creating those items and from shipping them. In 2021 alone, the report notes, Amazon operated 175,000 delivery vans, and more than 37,000 semitrailers.

For many who make online purchases, that impact is largely invisible; Kerr hopes this work sheds light on those consequences. “We just click a button and something shows up at our doorstep a couple days later,” he says. “And what people might not realize is that there’s such an enormous transportation infrastructure that’s needed to move goods from point A to point B, and we don’t see the toll that takes on air quality and health. But it’s certainly there.”