国家环保部首次对灰霾污染日给出详细定义，并正在公开征求意见。未来该标准将适用于全国城市或区域范围内的灰霾污染日判别与预报。

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A girl reads a book on her balcony as smoke rises from chimneys of a steel plant on a hazy day in Quzhou, Zhejiang province. Air pollution has become a growing concern for most cities in China. Reuters

A haze pollution day occurs when the average concentration of PM2.5 is above 75 micrograms per cubic meter and visibility is less than 5 km for more than six consecutive hours due to an increasing concentration of fine particulate matter in the air.

灰霾污染日指细颗粒物(PM2.5)平均浓度大于75微克/立方米，且因空气中细颗粒物浓度增加导致能见度持续6 小时低于 5.0公里的空气污染天气。

此次国家环保部给灰霾污染日(haze pollution day)给出的详细定义表明，灰霾污染本质为细颗粒物(PM2.5)污染，灰霾污染应以颗粒物(particulate matter)为首要判别指标。灰霾污染颗粒物成分中，工业粉尘(industrial dust)、黑碳(black charcoal)、有机碳(organic carbon)、硫酸盐(sulphate)、硝酸盐(nitrate)等粒子增加，二次生成在颗粒物(PM10)中所占比重提高，已经明显有别于自然形成的霾(主要由土壤尘、沙尘和海盐粒子组成)。

近两年来，雾霾(smog)天气频频造访国内各大城市，防雾霾口罩(anti-smog face mask)一度成为热销品，有些保险公司甚至顺势推出雾霾险(smog insurance)，中国科学院甚至计划建设雾霾实验室，专心研究防雾霾技术。