简单的讲，就象高考标准分（倒过来）：

最低0分，空气完美；
100分，空气一般（正好达标，但标准是人定的，因时间而异，因国家而异,  美国趋势是往下修订）；
最高500分，空气糟透了。

AQI是对每种污染物而异。

AQI PM10;  

AQI PM2.5;

AQI NOx;

AQI SOx;

AQI CO;

AQI O3.  

全国城市空气质量实时发布平台

http://113.108.142.147:20035/emcpublish/

中国环境监测总站 http://www.cnemc.cn/

关于雾霾全面论述看:

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我在博客发表了一篇文章：柴静没有回答的问题，我来试试(二)

 http://blog.sciencenet.cn/blog-2470641-873291.html  

此文来自科学网洪建辉博客
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空气污染指数, 英文缩写：AQI, Air Quality Index，可分六档 (中国版)
0-50： 空气质量I级，优，无污染
51-100： 空气质量Ⅱ级，良，对健康无危害
101-200：空气质量Ⅲ⑴级和Ⅲ⑵级，轻微污染和轻度污染，对敏感人群有危害
201-300：空气质量Ⅳ⑴级和Ⅳ⑵级，中度和中度重污染。对健康有比较严重的影响
超过300：空气质量V级，重度污染。所有人的健康都会受到严重影响

美国版:

http://www.epa.gov/airnow/aqi_brochure_02_14.pdf

Each category corresponds to a different level of health concern:

• Good. The AQI value for your community is between

0 and 50. Air quality is satisfactory and poses little or no

health risk.

• Moderate. The AQI is between 51 and 100. Air quality

is acceptable; however, pollution in this range may pose a

moderate health concern for a very small number of individuals.

People who are unusually sensitive to ozone or

particle pollution may experience respiratory symptoms.

• Unhealthy for Sensitive Groups. When AQI values

are between 101 and 150, members of sensitive groups

may experience health effects, but the general public is

unlikely to be affected.

• Ozone: People with lung disease, children, older adults,

and people who are active outdoors are considered

sensitive and therefore at greater risk.

• Particle pollution: People with heart or lung disease,

older adults,1 and children are considered sensitive and

therefore at greater risk.

• Unhealthy. Everyone may begin to experience health effects

when AQI values are between 151 and 200. Members of

sensitive groups may experience more serious health effects.

• Very Unhealthy. AQI values between 201 and 300

trigger a health alert, meaning everyone may experience

more serious health effects.

• Hazardous. AQI values over 300 trigger health warnings

of emergency conditions. The entire population is even

more likely to be affected by serious health effects.