The Environmental Protection Agency, together with other federal, state, local, and tribal agencies, developed AIRNow.gov, offering the public daily Air Quality Index forecasts and real-time Air Quality Index conditions for over 300 cities across the country as well as links to detailed state and local air quality cites.

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The government's Air Quality Index shows "unhealthy" pollution levels in much of Southern California.

CNN: Smoke a serious health threat as wildfires spread

An unofficial reading from the US embassy's air quality index recorded over 500 early in the morning, but changed to 168 as of 13:00 (05:00 GMT).

BBC: Smog and sandstorm engulf China's capital

Its report grades cities using, in part, the EPA's color-coded Air Quality Index, as well as its own weighting system that ranks the severity of pollution on a daily basis.

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But after just two nights, the government says the PM 2.5 air pollutant index has soared in Beijing, Shanghai, Nanjing, Hangzhou, Xian and other major cities, Southern Metropolis Daily reports.

BBC: China media: New Year haze

He and his colleagues have launched a new air-pollution index that he says captures health risks better than the official index, which has not kept pace with the latest science.

ECONOMIST: An encouraging appointment addresses an enduring problem

Loss of air conditioning creates big problems, this proven in the great Midwestern heatwave of 1995 (when the heat index reached a deadly 136 in southern Wisconsin).

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