This article was originally published by the Chesapeake Bay Journal, an award-winning nonprofit news organization that has been covering environmental issues in the Bay region for more than 30 years.
Over the past few decades, Cumberland Valley communities in southcentral Pennsylvania — home to the Interstate 81 corridor through Franklin and Cumberland counties — have seen rapid growth in the number and size of warehouses.
The industry, which includes fulfillment and distribution centers, has been a major economic boon. In those two counties, roughly 10% of workers are in the warehouse industry. But these massive facilities also draw air-polluting truck traffic.
Now, an analysis led by researchers at Shippensburg University reveals links between warehouse expansion, health risks and economic benefits within the Cumberland Valley.
The analysis shows that air pollution is higher within the valley, where warehouses are concentrated, than outside the valley. There have been improvements over the past decade, though, as clean air regulations reduced air pollution, even as warehouses and truck traffic increased. However, air pollution during some parts of the year still regularly hits the federal safety threshold and surpasses the stricter World Health Organization limit.
That means air quality is still a concern, said study author Tim Hawkins, a Shippensburg earth scientist. “But we’re allowing [warehouses] to be here as a society because there’s a lot of economic benefit,” he said.
The region became a draw for warehouses, in part, because of its geography. By way of Interstate 81 through the valley, trucks can reach about two-thirds of the U.S. population within about a day, Hawkins noted.
The area also boasts ample farmland adjacent to urban areas like Shippensburg and Carlisle — open space ripe for massive warehouse projects in close proximity to highways.
Amazon moved in, as did many retailers, such as Walmart, Target, Lowe’s and Home Depot, all of them building fulfilment centers for online shoppers.
Exhaust from diesel trucks stopping at these facilities contributes to a form of pollution known as particulate matter, or PM2.5. These tiny particles measuring 2.5 micrometers across or less can travel deep into the lungs and cause respiratory and even cardiovascular diseases.
To weigh the pros and cons of the warehouse boom, Hawkins, undergraduate researcher Grace Coffman and others collected data on the industry’s local expansion from the late 1980s through early 2020s. They also trained a computer model to identify fulfillment and distribution centers in aerial images of Cumberland and Franklin counties taken periodically from 2004 onward.
Records showed that there had been four such facilities in 1988. By 2022, there were about 200. The average size of new warehouses in the region doubled, from less than 10 acres in 2003 to more than 20 in 2022.
The team also tracked changes in truck traffic using PennDOT data on average daily tractor-trailer traffic surrounding Carlisle. From 2001 to 2023, that increased more than 20% on the Pennsylvania Turnpike and 43.5% on Interstate 81.
To gauge how air quality differs between the Cumberland Valley and the surrounding region, the researchers compared data from an EPA sensor in Carlisle with an EPA sensor south of the valley in Arendtsville. They also used readings from nine other sensors that generate publicly available data, eight of them within the valley and one just outside.
The two EPA sensors showed that average daily particulate matter levels are 14% greater, on average, in Carlisle than in Arendtsville. In winter, the particulate matter levels are 31% greater.
Of the nine additional sensors, the one outside the valley registered the lowest air pollution levels. Additional data from NASA satellites also suggested that particulate matter concentration is higher in the valley than in the surrounding area.
The authors attribute the heightened air pollution to the concentration of warehouses and associated truck traffic in the Cumberland Valley, as well as highway traffic in general. Valley geography also plays a role, Hawkins said. Mountains on either side of a valley often block wind that would otherwise carry pollutants away. And in winter, warmer air overtop a valley can act as a lid that traps colder air within the valley, along with pollutants.
The team also used an EPA model to predict the amount of pollution within the valley coming from warehouses specifically over time, based on emissions expected for a warehousing industry of a given size.
They found that PM2.5 emissions from warehouses declined in the Cumberland Valley by 45% between 2014 and 2020. Consequently, the monetized public health impacts associated with warehouses in Franklin County — a proxy for the valley as a whole — dropped by 66% over the same period.
Meanwhile, from 2017 to 2020, the local gross domestic product for the Franklin County warehousing industry grew by 30%.
Hawkins’ team attributes the decline in particulate matter to improvements in engine efficiency, as well as laws that prevent trucks from idling. “The Clean Air Act works,” Hawkins said. “Pollutants have come down at national levels, and so this is just a nice local example.”
Large drops in particulate matter levels over the past 20 years across the eastern U.S. are also linked to reduced emissions from coal power plants, said Daniel Goldberg, an air quality scientist at George Washington University in the District of Columbia, who was not involved in the study.
But despite improvements, summer and winter particulate matter levels in the Cumberland Valley still regularly bump up against the EPA’s limit for safe air and surpass the stricter World Health Organization limit, Hawkins said.
There are other environmental impacts of warehouses not captured in the study. In 2024, Goldberg and colleagues reported that concentrations of nitrogen dioxide, another diesel exhaust-related pollutant, are elevated by about 20% near warehouses across the country. But because the data was collected by satellites at a resolution of about 8 square miles, the authors do not know how pollutant levels may vary across individual neighborhoods. Some residents downwind of heavily trafficked warehouses may experience pollutant levels even higher than the estimate.
Warehouses, with their massive impermeable footprints, also create stormwater management challenges, Hawkins said. “You’re dumping warmer water, potentially, into the streams that historically have been groundwater fed.”
Kirk Stoner, director of planning for Cumberland County, said that the Shippensburg study “provides great information on air quality in our valley.” But as an advisor to the county’s 33 municipalities on zoning issues, he said he would be hesitant to use the study to make zoning guidelines for warehouses, or any other transportation intensive uses, because there are so many other contributors to air pollution in the valley, including highway traffic unrelated to the warehouses.
Cumberland Valley municipalities are now bracing for the next big development push: data centers, which can pollute the air with their backup diesel generators and, like warehouses, create stormwater management challenges.
Warehouse construction in Cumberland County, meanwhile, has slowed. Much of the available land close to interchanges has already been developed into warehouses, Stoner said. “Our municipalities don’t appear to be willing to rezone land that is farther away.”