Now we move on to the topic of transportation emission sources, specifically exhaust and non-exhaust emissions. We will also look into efforts to regulate these different types of emissions.

Key takeaways:

1. Exhaust emissions are those caused by the burning of fossil fuels in combustion engines, most commonly gasoline and diesel.
2. Non-exhaust emissions are particles released into the air from brake wear, tire wear, road surface wear and the resuspension of road dust during on-road vehicle usage.
3. Non-exhaust emissions are far less regulated than exhaust emissions in most parts of the world.