In August 2015 we decided to test the PM 2.5 levels from a 2013 Ford Explorer with a V8 engine. The nephelometer was positioned 15cm away from the exhaust pipe on a calm day. After several minutes of readings on a warmed up engine, the PM 2.5 levels ranged between 8 and 11 with a modal response of approximately 8.5. Here's a photo of the experiment,
This shows us how clean vehicles emissions are when compared to woodsmoke fires.