What is the relationship between ambient monitoring and PSD as described?

• A. PSD determines sampling locations.
• B. Ambient monitoring measures water quality.
• C. Ambient monitoring helps demonstrate air quality relative to PSD increments during permit determinations.
• D. PSD increments are unrelated to ambient monitoring.

Answer: (C)

Ambient monitoring provides the actual air quality data used to compare against PSD increments when deciding permits for new or modified sources. In the PSD program, certain pollutants have numerical increments that cap how much ambient concentration may increase without causing significant deterioration. When a permit is being considered, agencies use recent ambient monitoring data to see whether there is available increment and to gauge how much additional emissions the project could cause. This helps determine whether the project would exceed the allowed deterioration and what permit requirements or controls might be needed. Amb​ient monitoring isn’t about setting sampling locations or measuring water quality, and PSD increments are directly linked to the observed air quality data.