How to build a smog sensor with a ESP8266 microcontroller: 
Stuttgart, Germany has, like many other cities, a smog problem—even if it may be less severe than in other cities. The European Union has defined a threshold of on average 50 micrograms of dust particles per cubic meter in a 24-hour window of air to be allowed for a maximum of 35 days a year. For the last few years, actual values have been much higher for more than 35 days. There are governmental stations that measure the air pollution, but they can’t be everywhere for obvious reasons.
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