For geographic areas in which ambient pollutant levels are substantially below those prescribed by NAAQSs, the 1977 amendments asserted a congressional commitment to the principle of prevention of significant deterioration (PSD).

• 对那些大气污染物的浓度水平远低于《全国环境空气质量标准》的地理区域，1977年的修正案维护了国会防止显著恶化原则的责任。