660 data centers in Virginia.
21 NSR permits pending. Tier IV mandate hits July 1, 2026.

New Source Review (NSR) is a preconstruction permit. It governs whether a new or modified source of air pollution can be built and what control technology it must use. Title V is an operating permit. It rolls up all of a major source's applicable Clean Air Act requirements into a single document the facility operates under after construction. A new data center typically goes through NSR first to authorize the diesel generators and any other emission units. If the resulting potential to emit crosses Title V thresholds, the facility then needs a Title V operating permit to run.

A non-Title V air permit is a state-issued operating or construction permit for a source whose potential to emit falls below federal Title V major source thresholds. Many data centers, depending on generator count, generator size, and projected operating hours, are permitted as synthetic minor or true minor sources under state programs rather than as Title V majors. The choice has real consequences for monitoring, recordkeeping, and renewal cadence, and it should be modeled before generator counts are locked in, not after.

Data centers run banks of large diesel generators for backup power. Diesel combustion produces nitrogen oxides, particulate matter, carbon monoxide, sulfur dioxide, and air toxics, all regulated under the Clean Air Act. Even if the generators only run during outages and routine readiness testing, their potential to emit is calculated against permitted hours, not actual hours, which is enough to trigger NSR review and, in many cases, Title V operating permit obligations. Air permits are usually the slowest part of a data center build, slower than water or land use approvals.

New Source Review is the federal Clean Air Act preconstruction permitting program. For a data center, the NSR permit authorizes the construction of the diesel generator fleet and sets the emission limits, control requirements, monitoring conditions, and operating restrictions the facility must follow. Virginia DEQ currently lists 184 existing NSR permits and 21 active NSR applications associated with data centers. NSR is also where Best Available Control Technology determinations are made, which is the lever that the new Tier IV mandate pulls on directly.

Tier IV refers to the EPA non-road diesel engine emission standards, which are the most restrictive tier currently in force for new diesel engines. Tier IV-equivalent controls dramatically reduce nitrogen oxide and particulate matter emissions compared to older tiers, typically through selective catalytic reduction and diesel particulate filters. Virginia House Bill 507 directs Virginia DEQ to deny any air permit submitted for a data center generator on or after July 1, 2026 unless the generators are equipped with Tier IV emission controls or the environmental equivalent. Updated BACT guidance for both emergency and non-emergency diesel generator sets at data centers also takes effect for applications received on or after that date.

Timelines vary by state, by region within a state, and by how clean the application is on submission. Air permit applications are commonly the slow link in a data center schedule. The Northern Regional Office of Virginia DEQ has added requirements and new boilerplate language to the air permit application process that can extend review cycles when applicants do not account for them at the start of a project. The work that compresses the schedule happens before filing, not after, which is why pre-submittal scenario modeling and zone-of-impact analysis matter so much.

It depends on potential to emit. If the data center's permitted generator capacity, federally enforceable hour limits, and any other emission units sum to a potential to emit at or above the major source thresholds (typically 100 tons per year of any criteria pollutant in attainment areas, lower in nonattainment areas), it is a Title V major source and needs a Title V operating permit. Many large hyperscale campuses end up as Title V majors. Many smaller or capacity-restricted sites are permitted as synthetic minors under state programs to avoid Title V. The choice should be modeled, not assumed.

Community concerns about air quality, noise, water use, and cumulative impact have become a routine part of data center permitting in Virginia, Georgia, Texas, and several other markets. Public comment periods on draft NSR permits can extend timelines and can force additional dispersion modeling or health risk analysis if commenters raise specific receptor or environmental justice concerns. The defensible response is the same calculation the air district would run: a transparent zone of impact, an honest health risk assessment for nearby sensitive receptors, and a record that any reviewer can reproduce. That is the workflow LSARS is built for.