One of the air pollution detection machine in Beijing (at the American Embassy) is connected to Twitter and tweet about the air quality in real time. By default the machine in Beijing output the 24hr summary PM2.5 air pollution information. What is PM2.5 is define here
Next will be to compare the pollution level between different cities such as LA and Beijing. But it turns out the air quality data for California are not so easy to get programmatically.
Here is the code I used to produce this analysis:
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