The following areas, by county, have been designated as nonattainment areas by the EPA in Arizona:
Cochise County
- PM10 — Paul Spur/Douglas
Gila County
- PM10 — Miami
- SO2 — Miami
- SO2 — Hayden
- Lead — Hayden
Maricopa County
- PM10 — Phoenix
- Ozone — Phoenix
Pinal County
- PM10 — Hayden
- SO2 — Hayden
- Lead — Hayden
- PM10 — West Pinal
- PM10 — Miami
Pima County
- PM10 — Rillito
Santa Cruz County
- PM10 — Nogales
- 5 — Nogales
Yuma County
- Ozone — Yuma
- PM10 — Yuma
Counties with no nonattainment areas at this time:
- Apache County
- Coconino County
- Graham County
- Greenlee County
- La Paz County
- Mohave County
- Navajo County
- Yavapai County
Given the geographic stipulations mentioned above, sources must obtain ERCs if they emit more than:
- 50 tons/year of NOx
- 50 tons/year of VOC (Volatile Organic Compounds)
- 40 tons/year of SO2 (Sulfur Dioxide)
- 50 tons/year of CO
- 25 tons/year of PM
Both the Arizona Department of Environmental Quality (AZDEQ) and the Maricopa County Air Quality Department (MCAQD) implement the emission reduction credit program. New or modified major facilities in nonattainment areas must obtain ERCs to satisfy the offset ratio (1:1 – 1.2:1) requirements for proposed increases. Qualifying emissions reductions can be banked for later use or sale.