I would suggest you to contact SeeedStudio, we’ve been looking for information on the Air Quality Index and the data that we found is different from the one used in their examples. You can check this website, http://waqi.info//, it shows data that is based on the US EPA Standard, however, if you compare it with the data from SeeedStudio the numbers are very different.
You can contact them following this link http://support.seeedstudio.com/knowledgebase/.
For those who are interested, here is the verbatim answer from Seed:
We associate the values with local air quality. The return value is voltage indicating the air quality, but not aligned with other common standards.
The output values will differ from different environment, like pressure, humidity and temperature.
==> So I am guessing that what they mean is that their example does not use specific thresholds because of the different environment variables. Our readings are (within reasons) aligned with other air-quality sensors near-by that are reported on Waqi so I'm tempted to say that they can be used with a similar scale but obviously don't rely on it if you're running something missing critical.
Thank you for the update. We encourage you to share your results here in the Community once you’re done with your project, I don’t recall seeing any other thread were an Air Quality sensor was used so it would be a great contribution. Hopefully this information will be useful for other users.