Large national parks and wilderness areas are Class I areas, where very little deterioration of air quality (defined in terms of increments in ambient concentrations) is allowed.

• 大型国家公园和荒野地带属于第一类区域，在这类区域内，不允许有一点空气质量（以大气浓度增高表示）恶化现象，所有其他地区属于第二类。