By Peter Adams, Carnegie Mellon University
With U.S. electricity demand starting to rise quickly and expected to continue rising, largely because of the power needed for data centers that process artificial intelligence, people are looking for almost any potential solution.
And people are warning that the full projected demand may not actually develop, which could make massive investments in power plants unnecessary, raising Americans’ electricity rates even more.
U.S. Secretary of Energy Chris Wright is among those who have been promoting what might seem to be an attractive idea: “We have 35 gigawatts of backup generators that are sitting there,” he told an audience of natural gas industry leaders in December 2025. He was referring to diesel-fired engines at hospitals, office complexes, corporate campuses and even data centers to provide electricity if the grid goes down.
That amount of power would be a significant step toward meeting the nation’s expected energy needs, without needing new long-term investments in power plants or transmission lines. But it’s also vital to know, as Wright went on to note, that “emissions rules or whatever” mean those generators can’t just be turned on and left running when there’s not a power outage or other emergency.
As an environmental engineer who studies air pollution from the energy system, I believe this proposal is concerning. Those emissions rules are in place because diesel-powered generators are among the dirtiest sources of energy, emitting fine particulate matter and related chemicals. That is a pollutant whose total emissions from all sources are estimated to cause about 100,000 premature deaths every year in the U.S. And in fact, emissions regulations on backup generators are less stringent than other power sources because they are intended only to run in emergency situations.
If Wright’s idea took hold, diesel fumes would pour into the nation’s air, often near major metropolitan areas that already have air pollution problems. To see more closely what would happen, John Allen, a research assistant at Carnegie Mellon University, and I projected the effects on public health and air quality of running backup diesel generators at data centers.
Simulating the emissions of diesel generators
Comprehensive data is hard to nail down about locations of data centers and which ones have how many diesel generators on site. Nobody has yet made a detailed proposal for which generators might be switched on, or for how long, so we did an exploratory analysis.
We started with an online database of locations of data centers. We also found documentation suggesting there is at least 35 gigawatts of diesel-powered generating capacity at data centers across the U.S., so we allocated that amount, which Wright had mentioned, proportionally to each data center’s size.
We looked at a scenario where these generators ran continuously throughout the year, generating 310 terawatt-hours of electricity. The generators might be used less – Wright himself talked about running them for only “a few hours per year.” But once they’re allowed to be turned on for regular power generation, people might get used to having that electricity available.
We assumed that all diesel generators are relatively new and comply with the Environmental Protection Agency’s most recent and stringent standards, which took full effect in 2015.
We compared the air pollution created from the diesel generators with a scenario where that same amount of power – 310 terawatt-hours – came from the existing mix of power plants in regional electrical grids. This could happen if utility companies built more generation capacity of the same types that already exist in the region or built new transmission lines to deliver more power from elsewhere.
Because no air quality model is perfect, we used three different computer simulations, each of which has been published in scholarly research journals, to simulate what would happen to the diesel pollution and how people downwind would be affected.
Diesel is dirtier
We found that using diesel generators rather than grid electricity would cause significant amounts of fine particulate matter pollution that would be dangerous to people’s health.
The exact results varied with each simulation and with a range of assumptions about emissions from diesel generators. But in general, we found that using backup diesel generators this way would cause about 500 more premature deaths per year in the U.S. compared with getting the same electricity from the central grid.
In a scenario where diesel generators were somewhat dirtier than the most recent standards, one air quality model had more than 800 additional people dying prematurely each year nationwide.
In the counties that would be hardest hit by the diesel generators’ pollution, the concentrations of fine particulate matter would increase by 0.25 to 2 micrograms per cubic meter of air, depending on the location and other assumptions for our calculations. This might not sound like a lot, but most urban areas in the U.S. already have fine particulate air pollution that’s close to the EPA limit of 9 micrograms per cubic meter. Adding that much more pollution risks tipping those communities beyond federal standards.
The Clean Air Act requires states to adjust their emissions to meet standards, so upping pollution from backup generators would require other cuts in emissions, such as at power plants and transportation.
Inspection and maintenance challenges
The results concern us, but reality might be even worse. We assumed that diesel generators would meet the most recent Tier 4 EPA emissions standards, but they may be older or exempt for other reasons.
For all our simulations, we assumed inspections and maintenance would keep emissions controls functioning properly at all generators. Modern diesel particulate filters are effective at reducing emissions, though not eliminating them entirely. When those filters fail, emissions skyrocket. Monitoring and maintenance at all of the generators, if they were running continuously, would be a logistical nightmare for regulators and the owners of the generators, and likely expensive as well.
Historically, centralized power plants that have thorough on-site monitoring are the most likely to have emissions control equipment running correctly to reduce emissions verifiably. Shifting to smaller generator units in a wide range of locations creates more potential points of failure and makes it harder to figure out that something has gone wrong, and where.
In our analysis, we compared backup diesel generators with the current electrical grid, where 60% of generation is still from fossil fuels. Increasing generation from renewable energy sources, such as solar panels and wind power, could help meet the rising demand for power without the additional emissions of dangerous air pollution.
Peter Adams is a professor of civil and environmental engineering, and engineering and public policy at Carnegie Mellon University.
This article is republished from The Conversation under a Creative Commons license. Read the original article. Banner photo: Diesel generators sit outside a data center in Ashburn, Va. (Amanda Andrade-Rhoades for The Washington Post via Getty Images).
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