Part 1 of 13 in Thirteen Records. The long article, Data Centers Don’t Have an Environmental Record. They Have Thirteen of Them., rates thirteen kinds of environmental complaint against data centers. This series takes them one at a time.
I work at a local ISP in Northern Illinois and co-founded FD-IX, an internet exchange. I have no customer, vendor, or interconnection relationship with any facility or developer named here and no financial position in any of them beyond broad-market index funds. My industry grows with infrastructure investment in a general way, which is an indirect interest; the full disclosure is at the top of the complete article.
A data center burns nothing on a normal day. Its air quality record on that day is the record of the power plants that serve it, and those plants are not the same from one side of Illinois to the other. That is the first of the thirteen environmental records a data center carries, and it is the one most often argued from the wrong number.
The wrong number arrives two ways. The opposition carries a coal-heavy average north from a region that does not serve the site. The industry carries the state’s nuclear share, which does not serve the new load either. Both sides are using an average where the question is about a margin. This post sorts three versions of the grid claim against EPA’s own emissions accounting, with the Northern Illinois subregion numbers in a table, and says plainly what I could not find: a marginal-emissions profile for any proposed Illinois facility.
How the ratings work. Each complaint below is stated the way it usually arrives at a hearing and rated on the scale the full article uses. Systemic: documented at compliant facilities across multiple geographies. Regional: real, but only under specific geographic or operational conditions. Isolated: documented at one or few facilities due to misconduct or atypical design. Exaggerated: the concern is real but the figures are permit ceilings or worst cases, not operating norms. Selective: a legitimate concern applied only to data centers, not to comparable land uses. Misattributed: the harm is real but the source, geography, or cause is wrong. Contested: a plausible mechanism exists but causal documentation at compliant facilities does not. Fabricated: no credible evidentiary basis exists. Where I say I found no record of something, that means a search of public sources through October 2026, not paid databases or records requests.
Air Quality: The Grid
Claim: A data center brings its grid’s emissions with it. Tier: Regional.
True, and the size of it depends on which grid. eGRID 2023 shows a factor-of-four spread in NOx output across the subregions in the table below. [1] The subregion that includes ComEd’s Northern Illinois territory along with Ohio, Indiana, and parts of several neighboring states (RFCW) produces 0.422 lbs of NOx per megawatt-hour (MWh). The subregion that includes Missouri and Ameren’s downstate Illinois territory (SRMW) produces 0.787. Virginia’s subregion, SRVC, produces 0.282. The national average is 0.452. Across all subregions the range runs from 0.083 in upstate New York to 8.139 in parts of Alaska.
| Grid Region | Territory | NOx (lb/MWh) | Sulfur dioxide, SO₂ (lb/MWh) |
|---|---|---|---|
| SRMW | SERC Midwest (Missouri, downstate Illinois under Ameren) | 0.787 | 1.636 |
| RFCW | RFC West (N. Illinois under ComEd, Ohio, Indiana, parts of neighboring states) | 0.422 | 0.412 |
| U.S. National | National average | 0.452 | 0.359 |
| SRVC | SERC Virginia/Carolina (Virginia, Carolinas) | 0.282 | 0.152 |
| RFCE | RFC East (Mid-Atlantic, not Virginia) | 0.202 | 0.212 |
| NEWE | New England | 0.291 | 0.116 |
Source: EPA eGRID 2023 Summary Tables [1]; territory assignments from EPA Power Profiler [1a]
eGRID subregions are drawn for emissions accounting. They do not follow state lines, utility territories, or the footprints of PJM and MISO, the grid operators that actually dispatch the plants. EPA’s Power Profiler places Commonwealth Edison’s territory, which includes DeKalb, Kane, and most of Kendall County, in RFCW, Ameren Illinois territory downstate in SRMW, and the Quad Cities in MROW. For the Yorkville ZIP code it returns either RFCW or SRMW depending on which utility serves the parcel. [1a] One state carries three subregion averages.
Averages also are not the margin. The unit that serves new load varies by hour, node, congestion, and season, and I did not find PJM, MISO, EPA AVERT, or NREL Cambium data tying any proposed Illinois facility to a marginal-fuel profile, so I do not state one. Data center load growth as a grid planning and reliability problem is a separate question, covered in a separate piece on electricity.
Claim: Data centers here will emit like they do in coal country. The reverse claim: Illinois is mostly nuclear, so a data center here is clean. Tier for both: Misattributed.
Both carry the wrong average to a specific site. A site served by ComEd sits in RFCW at 0.422 lbs NOx per MWh; a site served by Ameren sits in SRMW at 0.787. [1][1a] An SRMW figure carried north is the wrong number in the wrong place. So is Illinois’s generation mix, 54.9% nuclear and 12.3% wind in eGRID’s 2023 state table, carried to any particular site. [1] Nuclear plants run as baseload, holding steady output around the clock rather than ramping to serve new demand, so the state’s clean production average is not what serves incremental load any more than the coal-heavy subregion average is.
Claim: On-site gas generation is cleaner than the grid. Tier: Contested.
This is the industry’s claim, and it has a real mechanism in the right place. In a coal-heavy subregion like SRMW, if a coal unit sets the margin at a given node and hour, a modern gas plant behind the meter can be cleaner than the unit it displaces. Establishing that takes hourly marginal-emissions data for the node, and I found no such analysis for any proposed facility. What holds without it is narrower: on-site gas puts a combustion source at the property line that grid service does not. That is a statement about where emissions land, not about the net total, and no party to an Illinois proceeding I reviewed has shown on-site generation reduces emissions relative to grid supply during the hours the facility would draw power. The Yorkville proposals avoid the question; Project Cardinal’s PUD agreement commits it to take all primary power from the ComEd grid. [11x]
What to ask for. A council cannot change the grid, but it can ask the applicant to say which utility serves the parcel and therefore which subregion’s average applies, and it can decline to accept either side’s statewide figure in the record. Where an applicant proposes on-site gas generation as the cleaner option, ask for the hourly marginal-emissions analysis for the node that would support the claim. If none exists, the claim is Contested, and the one thing on-site generation does for certain is put a combustion source at the property line. Project Cardinal’s agreement commits it to grid power, which takes the question off the table in Yorkville. [11x] Make that commitment explicit in any approval where it is being assumed.
What nobody knows. I found no hourly marginal-emissions analysis for any proposed facility in a coal-heavy subregion or in Illinois. With a facility’s load profile and generator emission rates, it would settle whether on-site generation is cleaner or dirtier than grid service at a given site, a question both sides argue from averages.
This is part 1 of 13 in Thirteen Records, a series that takes the long article Data Centers Don’t Have an Environmental Record. They Have Thirteen of Them. one topic at a time. Next: diesel generators, the part of the Northern Virginia air quality problem that does and does not transfer.
Cover photo: Wikideas1 / Wikimedia Commons, CC0
Citations
[1] U.S. EPA, eGRID 2023 Summary Tables, initial release January 15, 2025; rev2 released June 12, 2025 (summary tables PDF internal production date March 27, 2025). https://www.epa.gov/system/files/documents/2025-06/summary_tables_rev2.pdf (archived: https://web.archive.org/web/20261025155941/https://www.epa.gov/system/files/documents/2025-06/summary_tables_rev2.pdf). Three-decimal subregion output emission rates (Annual NOx and SO2, lb/MWh) as published on EPA’s eGRID Summary Data page, “eGRID with 2023 Data”: https://www.epa.gov/egrid/summary-data (archived: https://web.archive.org/web/20261017013542/https://www.epa.gov/egrid/summary-data). Table 4, “State Resource Mix (eGRID2023),” Illinois: total net generation 177,690,287 MWh; nuclear 54.9%, gas 16.0%, coal 15.3%, wind 12.3%, solar 1.1%.
[1a] U.S. EPA, Power Profiler (eGRID 2023 data), subregion lookup by ZIP code and utility, read October 23, 2026. ZIP 60115 (DeKalb), 60178 (Sycamore), 60506 (Aurora), 61101 (Rockford), and 61068 (Rochelle) return RFCW; 61820 (Champaign), 62701 (Springfield), 61602 (Peoria), and 62002 (Alton) return SRMW; 61201 (Rock Island) returns MROW; 60560 (Yorkville) returns RFCW for Commonwealth Edison and SRMW for Ameren Illinois and Corn Belt Energy. https://www.epa.gov/egrid/power-profiler (archived: https://web.archive.org/web/20261025155519/https://www.epa.gov/egrid/power-profiler)
[11x] United City of Yorkville, Ordinance No. 2025-77, approving the Planned Unit Development Agreement for Project Cardinal, passed November 10, 2025 (7-0), signed by the mayor November 13, 2025, published November 14, 2025; city-posted executed copy, mayor’s signature and clerk’s attestation dated November 13, 2025, Pioneer Development signature and date lines blank. Section 2.1: vesting applies “Upon commencement of the Project within three (3) years of the Effective Date.” Section 2.2: “Section 10-4-10 of the UDO is reserved for additional regulations applicable to Energy Industrial Uses. No new or amended standards, code provisions, or special regulations for Energy Industrial Uses shall apply to the Subject Property during the twenty (20) year vested term from the Effective Date of this Agreement, unless Developer agrees in writing or to the extent required by state or federal law.” No reference to Ordinance 2025-53. Section 2.14: “seventy-eight (78) feet, inclusive of any rooftop mechanical equipment or appurtenances.” Section 3.5: water obligations “addressed exclusively in the Utility Agreement.” https://www.yorkville.il.us/DocumentCenter/View/13587/Ordinance-2025-77—record?bidId= (archived: https://web.archive.org/web/20261025151237/https://www.yorkville.il.us/DocumentCenter/View/13587/Ordinance-2025-77—record?bidId=). Annexation agreement, Ordinance No. 2025-78: https://www.yorkville.il.us/DocumentCenter/View/13588/Ordinance-2025-78—record?bidId= (archived: https://web.archive.org/web/20261025151421/https://www.yorkville.il.us/DocumentCenter/View/13588/Ordinance-2025-78—record?bidId=). Packet version: City Council Packet, November 10, 2025 (ArchiveCenter Item 6499), Planned Unit Development Agreement between the United City of Yorkville and Pioneer Development, LLC (Project Cardinal), packet pp. 272 to 290. Section 2.1: entitlements “fully vested and protected from amendments and changes to City ordinances, codes, or regulations for a period of twenty (20) years from the Effective Date.” Section 2.2: “No new or amended standards, code provisions, or special regulations for Energy Industrial Uses shall apply to the Subject Property during the twenty (20) year vested term from the Effective Date of this Agreement, unless Developer agrees in writing or to the extent required by state or federal law.” Section 2.3: approximately ten-year build-out; Phasing Plan “advisory only and non-binding.” Section 2.4: “All data center buildings shall be at least five hundred feet (500′) from the nearest residential or commercial structure outside the boundaries of the Subject Property,” measured “from existing, occupied, residential or commercial buildings as of the date of PUD approval.” Section 2.10: 100-foot Transition Zone Type D buffer with a 12-foot berm facing residential properties and 8 feet elsewhere; “No additional berms or landscape requirements shall be imposed unless Developer agrees in writing.” Section 2.11: “the most appropriate location for Mechanical Equipment is on the rooftops; therefore, whenever practical, mechanical equipment shall be placed on the rooftops”; project subject to the City Noise Ordinance “as it existed when the PUD application was approved by the City Council.” Section 2.14: 78-foot maximum height including rooftop equipment. Section 2.17: “all primary power used for the data center campus on the Subject Property will be delivered from the Commonwealth Edison power grid” unless the City Council approves otherwise. Section 3.4: continuous noise monitoring devices at the onset of each construction phase, a preliminary report within 60 days after each building is operational, devices maintained for the life of the project. Section 3.11: operational testing of generators “during the hours of 11:00 a.m. to 5:00 p.m., Monday through Friday, and not on any Holidays.” https://www.yorkville.il.us/ArchiveCenter/ViewFile/Item/6499 (archived: https://web.archive.org/web/20261025154939/https://www.yorkville.il.us/ArchiveCenter/ViewFile/Item/6499)