What percentage of airports in nonattainment areas must conform to State Implementation Plans (SIPs)?

• A. 10 percent
• B. 25 percent
• C. 50 percent
• D. 75 percent

Answer: (B)

Air quality conformity is about making sure airport development does not jeopardize the air standards set in the State Implementation Plan. In areas that don’t meet those standards (nonattainment areas), the rule specifies a minimum share of airports that must conform to the SIP. That minimum is 25 percent, meaning at least a quarter of airports in nonattainment areas must have projects evaluated to show emissions stay within the SIP’s budgets and align with the plan’s pollution-reduction strategies. This threshold helps protect air quality progress while keeping the process workable.