In August 2015 we decided to test the PM 2.5 levels from a 2013 Ford Explorer with a V8 engine. The nephelometer (Radiance Research M90 ) 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. Paradoxically you would be safer (at least from a PM 2.5 perspective) breathing off this tailpipe like a snorkel than living near a wood fire like this where readings have sometimes hit 200 (ten times the provincial limit).