Aqui

Frugal, portable air quality meter for your phone. Buy an SDS021 or an SDS011 and plug it in your phone using an adapter. This app will show you the PM2.5 and PM10 concentration levels.

SDS021 is USD20. and SDS011 and USD 17. A USB adapter doesn't cost more than two dollars. This makes it possible to have a very low-cost air quality monitor.

Step 1) Buy the sensor (SDS021) from AliExpress

Step 2) Buy the adapter (I bought it from eBay.in)

Step 3) Download the app

Step 4) Open the app

Step 5) Plug in the sensor

Step 4 and step 5 should not be interchanged!