Had a look at sample code of groove dust sensor

Products & Technology Grove
2

Hi there,


Grove-Dust sensor uses counting method to measure dust concentration, not weighing method, and the unit is pcs/L or pcs/0.01cf. It measures PM whose size is around 1 micro meter
or larger.

For PM2.5, please refer to http://wiki.seeedstudio.com/Grove-Laser_PM2.5_Sensor-HM3301/ thanks.

best rgds
Bill