What are the NAAQS criteria pollutants?

The National Ambient Air Quality Standards (NAAQS) regulate six "criteria" pollutants: particulate matter (as PM2.5 and PM10), ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. The EPA sets a primary standard (to protect human health, with an extra margin for sensitive groups) and, for some pollutants, a secondary standard (to protect welfare — visibility, crops, buildings) for each one, and reviews the standards periodically as health science evolves.

What is the difference between a Title V permit and a minor source permit?

A Title V (operating) permit is required for "major sources" — facilities whose potential emissions exceed statutory thresholds (commonly 100 tons/year of a criteria pollutant, lower in some nonattainment areas, or 10/25 tons/year of hazardous air pollutants). It consolidates all applicable federal, state, and local air requirements into one comprehensive, publicly reviewable document with ongoing monitoring, recordkeeping, and reporting obligations. Facilities below the major-source thresholds instead need a simpler minor-source (or synthetic minor) permit with fewer ongoing obligations.

What triggers New Source Review (NSR)?

New Source Review is triggered when a facility is newly constructed or undergoes a "major modification" that would significantly increase emissions of a regulated pollutant above defined thresholds. In attainment areas, this brings Prevention of Significant Deterioration (PSD) review, requiring Best Available Control Technology (BACT) and air-quality modeling to show the new emissions will not violate the NAAQS. In nonattainment areas for that pollutant, the stricter Nonattainment NSR applies, requiring the Lowest Achievable Emission Rate (LAER) and emission offsets from other sources.

What does an engineer typically do in air quality permitting work?

Engineers supporting air permitting calculate potential and actual emissions for each process (using AP-42 emission factors, mass balances, or stack testing), determine which permitting thresholds and applicable requirements are triggered, evaluate and select control technologies to meet those requirements, and prepare the technical permit application, including any required air dispersion modeling to demonstrate NAAQS compliance at the facility fence line and beyond.

Engineering·12 min read·July 12, 2026

🏭 Air Quality Permitting & NAAQS Compliance for Engineers

A practical guide to U.S. air quality regulation — the NAAQS criteria pollutants, how Title V and New Source Review permitting work, and the engineer's role in emissions calculations and control technology selection.

📖Environmental & Water Resources Engineering Handbook (Full Access)

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Why Air Quality Is Regulated

Unlike a discharge pipe into a river, air pollution has no fence — emissions from a single stack disperse over an entire airshed and mix with emissions from every other source nearby. Regulating air quality therefore requires two linked tools working together: national health-based standards for what the ambient air should contain, and a permitting system that controls how much any individual source is allowed to emit. Environmental engineers sit squarely in the middle of both, translating a facility's processes into emissions numbers and a permit application that regulators can act on.

Topics covered

air quality permittingNAAQScriteria pollutantsTitle V permitNew Source ReviewPM2.5PM10ozonecarbon monoxidesulfur dioxidenitrogen dioxideleademissions calculationscontrol technologyClean Air Actattainment area