They are mammoth warehouses large enough to fit football fields inside them, handling many of the more than 20 billion packages Americans send and receive each year.

But for people who live around them, the round-the-clock semitrailer traffic at these giant hubs significantly worsens air pollution, according to a new Nasa-funded study that tracked pollutants from space.

The research, led by scientists at George Washington University, is the first of its kind; it used satellite technology to measure a harmful traffic-related pollutant called nitrogen dioxide, zooming in on nearly 150,000 large warehouses across the United States. They found that nitrogen dioxide, which can lead to asthma and other health problems, jumped 20% on average near the warehouses. At the busiest facilities the increase was higher.

“The average warehouse built since about 2010 looks a lot different than the warehouses that were built prior to that, with lot more loading docks, a lot more parking spaces,” said Gaige Kerr, the lead author of the study and an assistant research professor of environmental and occupational health at the Milken Institute School of Public Health of George Washington University.

“They’re also increasingly being built in dense clusters next to other warehouses, and attract a lot more traffic, specially heavy-duty vehicles. And that’s very bad when it comes to pollution.”

The research underscores how logistics hubs have fast become a significant contributor to pollution as American heavy industry, a traditional source of pollution, has receded over the past decades and as the power sector has cleaned up its power plants.

Facilities like these have increasingly attracted regulatory and legal attention.

In one early case in 2011, Kamala Harris, then California’s attorney general, challenged a proposed million-square-foot warehouse complex in Southern California, saying communities around it were disproportionally affected by diesel exhaust.

That legal challenge resulted in a settlement in which developers of the warehouse agreed to reroute traffic, conduct air quality monitoring, plant trees and bushes to buffer against air pollution and install air filters in nearby homes.

E-commerce has only grown since the California case. That growth accelerated particularly during the Covid pandemic, prompting a new round of warehouse construction.

The researchers, who looked at traffic information from the Federal Highway Administration and demographic data from the Census Bureau, also found that communities with large racial and ethnic minority populations were often located near warehouses and inhaled more nitrogen dioxide and other pollutants.

They found, for example, that the proportion of Hispanic and Asian people living close to the largest clusters of warehouses in the study was about 2.5 times the nationwide average.

The study also found that a fifth of all of the warehouses were concentrated in just 10 counties, including Los Angeles County, California; Harris County, Texas; and Miami-Dade County, Florida.

The researchers said that nitrogen dioxide was only one of many pollutants that people who lived near ecommerce hubs were exposed to. Nitrogen dioxide is relatively easier to study from space than some others, Kerr said. “But in the future would be great to understand other pollutants that are relevant for health, like particulate matter or black carbon.”

California has moved to regulate pollution from warehouse hubs, adopting a rule in 2021 that would force facilities to clean up their emissions. The rule, affecting about 3,000 of the largest warehouses in the state, requires operators to slash emissions of nitrogen oxides and other harmful pollutants from the trucks that serve the sites, or take other measures to improve air quality. 

 - NY Times