The Alphasense OPC-N2 is a relatively inexpensive (~$450) optical particle counter that can be used as a proxy for particulate matter loadings in the atmosphere. It suffers many of the same shortcomings as other inexpensive particle measurements based on light scattering, but its optics are better than most alternatives (Dylos DC1100, Shinyei, Somyoung, Sharp, etc). One huge advantage is that it gives you 16 discrete size bins ranging from 380 nm to 17.5 um. This is quite a bit better than its competitors, although no where near ideal for particle measurements (I would like to see one < 100 nm to capture the mode).
I have used this device in my own work, and thus wrote a little python library so that you can easily interface the OPC with a Raspberry Pi over the serial interface to make it a bit more portable. The library is tested on both the OPC-N1 and OPC-N2 and logs the values that are recorded on the device using Alphasense' firmware.
You can find the library on github under an MIT license. Please use it and link back to it! Issues can be logged through github, and pull requests can be sent if you have improvements.
This article will be updated once I have time to write a proper tutorial..