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Expert warns diesel backup generators at AI centers could raise local PM2.5 and linger under inversion layers
Summary
The commission heard that backup diesel and natural-gas generators used to meet 99.999% uptime can emit locomotive-level pollution and that Sunnyvale currently lacks local air-quality monitors to track those emissions, which are exacerbated by frequent inversion layers in the Bay Area.
Meshika Allgood told commissioners that AI facilities aim for extremely high availability—"5 nines" or 99.999%—and that any variability in grid power is covered by backup generators that can match the pollution output of a diesel locomotive. "A single data center facility may rely on 40 to 53.25 megawatt diesel generators," she said, adding that generators emit PM2.5, NOx, CO and SO2.
Allgood also said the Bay Area Air District and state agencies have been engaged in petitions and rulemaking but that Sunnyvale has no local air-quality monitors; the nearest monitors listed by the Bay Area district are in Fremont and South San Jose. She noted that the region’s near-constant inversion layers can trap pollutants and extend exposure downwind.
The presenter cited the Great Oaks South case in San Jose where the California Energy Commission (CEC), as lead agency in a specific proceedings, overruled air-district modeling concerns and approved findings. Commissioners raised whether Sunnyvale could require co-located clean energy or ban continuously operating fuel-based generation; the presenter said city-level ordinances or permitting conditions are one path cities have taken.
