I've just finished washing my bike after a rainy-night-ride and have noticed;

1. Air on Tokyo road is filled with exhaust fumes.
2. The right side of wheel rim is so much dirtier than the left side. Because cars always on the right side of me and my bike.
3. Those fumes sink and float on very near of the road. While my helmet and front bag were almost clean, wheel rims were perfectly painted with blacky stickies. It means that surface of the road and air near the ground are so toxic especially on rainy day.