Some motorist really do try to screw with cyclist
A couple of days ago on a rare warm day this spring, I was out riding my trike. I pulled up to a street crossing on the MUP and was waiting for traffic to clear so that I could cross. A jerk in a one ton diesel pickup went by, and just as he did he laid the throttle to the floor and belched out a huge cloud of black smoke. Since I was on the trike and at the level of the exhaust pipe, I got the full effect of the smoke. Im sure the idiot thot it was funny.
Health Effects of Diesel Exhaust
One thing not mentioned above is that diesel smoke has health effects. This soot is made up of extremely small particles which can get very deep into the lungs, into the air sacs themselves (alveoli) and then be absorbed directly into the blood stream. They have an effect on the heart, where if a person already has coronary artery disease, they can precipitate a heart attack.
Even without the underlying heart disease, diesel exhaust is bad for your health.
So if someone does this "smoking" to you, try to hold your breath and not breathe that stuff!