index of atmospheric purity

例句：

1. 1.The index of atmospheric purity is a crucial factor in determining the health of the environment.
   大气纯净度的指数是决定环境健康的关键因素。
2. 2.The government has set a target to reduce the index of atmospheric pollution by 20% by 2025.
   政府已设定目标，到2025年将大气污染指数降低20%。
3. 3. The index of atmospheric purity is closely monitored by scientists and environmentalists around the world.
   大气纯净度的指数由世界各地的科学家和环保人士密切监控。