严重的雾霾天气中大气的细颗粒物(PM2.5)，危及人们的身体健康和城市的正常生活。
O O O B-Thing I-Thing O O O O O O B-Thing I-Thing I-Thing I-Thing O B-Metric B-Thing I-Thing I-Thing I-Thing O O O O B-Person I-Person O O O O O O B-Location I-Location O O O O O O