Air quality concerns raised over data centre plans

Kieran Molloy, Local Democracy Reporter

Concerns have been raised about the impact controversial plans for a data centre will have on the air quality for local residents.

In January 2026 Curtis Hall Ltd submitted plans to Cardiff Council to build a data centre on the site of the Cardiff East Park and Ride in Llanrumney.

In the application’s air quality assessment, under a section labelled “Use of the emergency backup generators for more than 30 minutes”, the application reads: “It is likely that the short-term impact of NO2 (nitrogen dioxide) emissions from the backup emergency generators, when operated more than 30 minutes, would result in the exceedance of the short-term NO2 air quality objective for the protection of human health.”

It continues: “Therefore, in case of the emergency use of the backup generators at the data centre, it is recommended that the operators take the additional precautions to limit exposure such as informing the neighbouring residents to stay inside and keep windows closed.”

In a further assessment from April 2026 guidance on the backup generators changed to say that each of the backup generators would be tested individually each week and the nitrogen dioxide levels emitted were “considered acceptable for the protection of human health”.

Despite this two members of the Senedd are still concerned about the impact the fumes could have on residents if the development went ahead.

In a joint statement to the Local Democracy Reporting Service (LDRS) MSs Nick Carter and Zaynub Akbar said: “People in Llanrumney should never be told that breaching air quality standards next to their children’s school is acceptable.

“But that is exactly what nearby homes and Glan-yr-Afon Primary School are facing even under the developer’s own revised modelling, which still predicts up to three breaches of safe nitrogen dioxide levels a year.

“The applicant’s original air quality assessment found that running backup generators for more than half an hour would likely breach safe nitrogen dioxide limits and their advice would have been that nearby residents should stay indoors with their windows shut.

“After questions from Cardiff council the applicant narrowed the testing conditions, testing generators one at a time instead of together, and revised the modelling to show the impact as ‘acceptable’.

“The developer says that is fine because it falls under an annual limit. We do not agree.”

Recently the Welsh Government issued a holding directive against the plans, which prevents Cardiff council from approving the application while the Welsh Government considered whether they should be the final decision-makers – a move welcomed by the two MSs.

The directive does not stop the council from debating or refusing the application.

The directive came after public outrage from the local community in which multiple campaigns against the data centre have been launched.

One campaign was led by Cllr Joe Carter who represents the ward the centre is planned in.

Regarding the original assessment the councillor for Pentwyn told the LDRS: “The proposed data centre is not only taking away a much-used hospital park and ride, removing open space, and creating water issues, it risks poisoning the air we breathe as well.

“The fact that the developers admit in their own documents that to use the diesel generators for more than 30 minutes would create a health risk is very worrying.

“This development brings no benefit to Pentwyn and surrounding communities and only brings potential harm to our health and our environment. It must be stopped.”

Curtis Hall Ltd has denied claims the data centre’s backup generators would pose a risk to the health of local residents.

‘Outdated’

A spokesman for the developer told the LDRS: “The suggestion that the current proposals acknowledge a health risk from operating the backup generators for more than 30 minutes is based on an outdated assessment from December 2025 and does not reflect the scheme currently before the planning authority.

“During the planning process the proposals were updated to use newer, lower-emission generators, supported by a further air quality assessment submitted in April 2026.

“That modelling assessed impacts at sensitive locations, including nearby homes, schools, and care homes, and concluded that the proposed scheme is acceptable in terms of protecting public health.”

They went on to say that it is “incorrect” to suggest the assessment was made acceptable by narrowing the testing conditions and the testing requirements have not changed with “routine testing” always having involved running one generator at a time for 30 minutes.

‘Lower-emission generators’

The spokesman added: “The key change was the use of newer, lower-emission generators. The national air quality standards have not changed either and the updated assessment demonstrates that the scheme meets those standards.

“These generators are for emergency backup only and would be used in the unlikely event of a grid failure. The updated assessment considered an extreme 72-hour outage, which National Grid data indicates might occur only once in 10 years.

“Even in that scenario the combined risk of exceeding the one-hour limit is around one in a thousand, which regulators regard as not significant.

“References to residents staying indoors with windows closed therefore relate to the earlier December 2025 assessment and should not be presented as advice applying to the updated scheme.”

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