[ 29 - dust (and cigarette smoke) ]
- http://aqicn.org/sensor/
- http://www.howmuchsnow.com/arduino/airquality/
- http://irq5.io/2013/07/24/testing-the-shinyei-ppd42ns/
- http://geojournalism.org/2014/04/dustduino-arduino-uno-edition/
- https://github.com/empierre/arduino/blob/master/DustSensor_Shinyei_PPD42NS.ino
- https://github.com/shadowandy/Arduino-Dust-Sensor/blob/master/ESP8266_DustSensor_ThinkSpeak_Interrupt/ESP8266_DustSensor_ThinkSpeak_Interrupt.ino
- http://wiki.seeedstudio.com/wiki/Grove_-_Dust_Sensor