Which statement best describes ambient air monitoring and how the data are used to evaluate compliance with the National Ambient Air Quality Standards (NAAQS)?

• A. Monitoring indoor air quality at buildings to assess occupant comfort.
• B. Ambient monitoring data are used only for historical archival purposes and not for compliance decisions.
• C. Ambient monitoring is used to adjust industrial emission permits directly at source.
• D. Measuring outdoor air pollutants at fixed stations or mobile platforms; data used to determine exceedances, trends, and to inform SIP development and compliance decisions.

Answer: (D)