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Data Centers and the Air District
Learn how the Air District regulates sources of air pollution at data centers.
What the Air District regulates at data centers
The Air District regulates stationary sources of air pollution at data centers, which are predominantly backup generators. The Air District does not regulate the data center as a whole facility.
A data center is a physical facility that houses and runs large, networked computer systems and servers to process, store, and distribute large amounts of data. Data centers support core applications like artificial intelligence (AI), e-commerce, online communication, cloud computing and storage, content delivery and streaming, and autonomous vehicles. Data centers often rely on diesel generators for backup power. Harmful emissions from diesel generators can pose health concerns, especially in communities overburdened by pollution.
Where the Air District fits in the process
Data center projects go through extensive local land use permitting and review under the California Environmental Quality Act (CEQA) before the Air District receives a permit application. The Air District’s role begins when an applicant submits a permit application for backup power equipment. As a result, the Air District’s review is one step near the end of a much longer local approval process.
The Air District does not decide whether a data center is built or where it is built. Site approval, zoning, and overall project approval are decided by local governments and other agencies. To learn how to apply for an Air District permit, visit the Permit Instructions page.
Which equipment needs an Air District permit
Most stationary sources of air pollution need an Air District permit. At data centers, this includes diesel and natural gas backup generators. The Air District requires permits for these engines because they emit pollutants, including diesel particulate matter and nitrogen oxides, that affect air quality and health. Diesel particulate matter is a toxic air contaminant that can increase cancer risk and contribute to heart, lung, and brain disease. It is soot created directly from combustion. Nitrogen oxides contribute to ozone and fine particle pollution, which can worsen asthma and other respiratory conditions.
Some backup power does not need an Air District permit:
- Fuel cells are generally exempt from permitting. Larger installations, roughly 20 megawatts (MW) and above, require a Health Risk Assessment to confirm the exemption still applies.
- Batteries and other zero-emission backup power are exempt from permitting.
What is required before the Air District issues a permit
An applicant must meet the following requirements before the Air District issues an authority to construct (approval to begin building the equipment):
- Emissions controls. The Air District determines whether Best Available Control Technology (BACT) is required, based on a 24-hour emergency operating scenario. If BACT is triggered, diesel engines must meet Tier 4 emissions standards, the lowest-emitting diesel engine technology available under federal emission limits.
- Health risk review. If the toxic air contaminant emissions exceed Air District trigger levels, the Air District completes a Health Risk Assessment. A Health Risk Assessment estimates the cancer and other health risks to nearby residents and workers from exposure to the project's emissions. The assessment not only accounts for the applied for project emissions but also accounts for all other sources at the facility permitted in the past 5 years, so the risk reflects recent additions and not only the new project. A facility includes all sources or buildings on contiguous or adjacent properties that are under common control and in the same major industrial grouping.
- More health-protective limit in overburdened communities. A more health-protective cancer risk threshold applies in overburdened communities.
- Emergency use, or stricter requirements for prime use. Backup generators are permitted for emergency use. Permits do not allow the engines to be used to support the electric grid. An engine that would run as a regular source of power, known as prime use, must meet stricter requirements.
- Public notice. The Air District issues a public notice when an application is for equipment within 1,000 feet of a K-12 school, or when it requires a Health Risk Assessment and is located in an overburdened community. The Air District posts notices on the Recent Permit Applications Received page, which explains how to comment. Anyone can also comment on any permit application, whether or not it requires a formal public notice and comment period, and the Air District responds to all comments before issuing it.
Ongoing requirements after a permit is issued
Owners must follow operating requirements for as long as the equipment runs:- Keep records of maintenance and testing.
- Keep records of emergency use and nature of each emergency.
- Stay within the limits on operating hours for maintenance and testing.Conduct periodic source testing to confirm compliance with emissions limits, unless the engine is EPA certified. Testing also happens at startup.
- Report annually the hours of maintenance and testing and of emergency use. This report is required to renew the annual Air District operating permit.
Have a comment?
General comments about data centers: Share your input with the Air District using the public comment tool.
Comments on a specific permit application: Comments on a particular project should go through that project's public notice so they become part of the permit record.
- See permit applications on public notice for instructions on where to submit comments.
- See permit applications received to sign up for notifications of new applications.
- Read the Air District's guide to making effective comments on permit applications.
Sign up for notifications and updates about rulemaking: To receive email notifications about rulemaking and related information from the Air District about backup generators, including those at data centers, please sign up for the Air District’s Rules and Regulations Email List below.
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Last Updated: 10/16/2026