Satellite Analysis Suggests Nitrogen Oxide Emissions at Southaven Turbine Field Far Above Permit Levels

A newly revised arXiv preprint says NASA’s TEMPO air-pollution satellite estimated nitrogen oxides, or NOx, emissions from the Southaven, Mississippi, turbine plant serving xAI’s Colossus 2 data center at an average 870 kilograms per hour after February 2026, roughly 19 times the level implied by the site’s state permit.

The paper, posted on arXiv as version 3 on Oct. 19 by Kevin D. Gauld, Daniel J. Varon, Nicholas Balasus and Daniel H. Cusworth, is a preprint and has not been peer-reviewed. It uses hourly nitrogen dioxide observations from NASA’s TEMPO instrument, a geostationary air-quality sensor over North America, to identify a new local plume after the plant began operating in late 2025. The authors then estimated two-week-average NOx source rates from August 2025 through August 2026 and calibrated that satellite method against continuous emissions monitoring system, or CEMS, data from U.S. power plants.

The facility is the turbine field at 2875 Stanton Road in Southaven, just south of Memphis, that powers the Colossus 2 data center in the Memphis area associated with xAI. According to the paper, TEMPO first detected the source in December 2025 at 530 plus or minus 220 kilograms of NOx per hour. Emissions then increased, with the study reporting an average of 870 plus or minus 165 kilograms per hour after February 2026.

That comparison matters because the study ties its estimates to the site’s permitting record. The authors say the post-February average was “roughly 19±4 times higher than expected from the facility’s March 2026 permit for 41 turbines operating under best available control technology (BACT) requirements (~47 kg h−1).” A Mississippi Department of Environmental Quality agreed order dated July 30 adds a key piece of context. It says, “MZX operates sixty-nine (69) portable, temporary simple cycle natural gas-fired combustion turbines” at the Stanton Road facility. The order also says 14 SMT-130 units had selective catalytic reduction, or SCR, and oxidation catalyst controls, and notes that a March 11, 2026, Prevention of Significant Deterioration permit had been issued for 41 stationary turbines.

In plain terms, the permit comparison is significant because the state permit assumed a smaller fleet of controlled turbines, while the later agreed order documented a larger temporary build-out and said only some units had SCR, a common pollution-control system for NOx. The paper says nearby sources do not explain the plume it detected, including the adjacent Tennessee Valley Authority combined-cycle plant, whose emissions during comparison periods were roughly 20 to 25 kilograms of NOx per hour.

The authors also emphasize limits to what the satellite analysis can show. These are satellite-derived estimates calibrated against other power-plant data, not direct stack measurements at the Southaven site. The paper reports uncertainty ranges around its estimates, and it says emissions at the expected permit level would have been undetectable with this TEMPO analysis. That means the study is not evidence, by itself, of a permit violation or illegal operation. It is an atmospheric estimate of a source strong enough to stand out from space.

Even with those caveats, the findings point to a broader accountability shift. TEMPO measures NO2 every hour, a much higher frequency than older satellites that often passed over once a day. That makes it possible to combine repeated observations and spot persistent plumes from individual facilities that might previously have been hard to isolate. In this case, the paper argues that fast-built gas power infrastructure for an AI data center left a detectable atmospheric signal.

The Stanton Road site was already under legal and regulatory scrutiny before the revised preprint appeared. The NAACP and the NAACP Mississippi State Conference sued X.AI Corp. and MZX Tech LLC on April 14, alleging unpermitted turbine operation and seeking relief under the Clean Air Act.

But the larger takeaway from the new paper is not limited to one project. As AI data centers push demand for rapid, on-site or near-site generation, satellite instruments such as TEMPO are emerging as an independent way to track pollution from those power systems, even when direct on-site emissions data are not publicly available.