A place I used to live, Fort Collins, Colorado, was the last city or civilization of any kind before the open prairie that led one to the Wyoming border, which was about thirty-some miles due north. 
Fort Collins, or 'FoCo', as the locals called it, was a college town. And into that town occasionally rolled The Carbon Boys from up Wyoming way. 
Down College Avenue they would roll, in their diesel pickups with big fat tailpipes, or 'smokestacks' even, rising up custom-made from out of the truck bed right behind the cab. Some had just one big fat exhaust pipe. 
It was a show of machismo, you bet, like driving a lifted truck with big fat tires but what was so startling about The Carbon Boys was their utter disdain for the environment because when their diesel pickups accelerated away from a traffic light that they had been idling at, a huge black cloud of diesel soot filled the air in their wake. I remember seeing a Toyota Prius being totally enveloped in one such cloud. 
This soiling of the environment was great fun for The Carbon Boys, who I learned to dread and avoid. Every time I saw one I would make damn sure I wasn't behind or near to them at the light and every time I witnessed 'the cloud' they left behind I thought "There oughta be a law against that!" but there wasn't. I never saw a cop pull one of these guys over. 
Fort Collins was part of Larimer County, and residents there had to get their cars smog checked every year in order to renew their registrations and I thought "Why do we have to get smog checks when people that own diesel trucks don't?!".
Well, two things. Number one, many diesels at the time were exempt from smog checks in Larimer County (not so anymore) and number two, The Carbon Boys always came from out of state. Typically windy Cheyenne, Wyoming, was where most of these trucks came from. Wyoming didn't have any vehicle emissions requirements, which certain counties in Colorado had, but more than that it was The Carbon Boys' 'in your face I'm going to pollute the air- your air'- mentality that was troubling. 
Why would anyone want to pollute the air around them to the extent that The Carbon Boys did was the question because even though the boys came primarily from Cheyenne, the majority of the people there didn't want bad air and drove nice clean running trucks and cars.

This phenomenon kinda came out of nowhere. The first time I witnessed it I was shocked but then it (unfortunately) became rather commonplace, especially on weekends when The Carbon Boys tended to roll on down to FoCo and cruise the streets. 
I wanted to study these people, like they were glaring anomalies of the tribe human (which they certainly were) but was turned off by the negativity that I was sure to encounter. Did they not love the environment like everybody else? No! They treated the environment with contempt bordering on the suicidal. That was what was so troubling about them. They were apocalyptic people and delighted in spewing filth into the air around them, filth that they wouldn't be breathing- at least not right away, but eventually they would. Did they not get that part of the equation? 
Not wanting to delve into the twisted psyches of the perps, I looked into the mechanics of diesel engines and exhaust instead, for at the time I occasionally drove a diesel bus at work and that thing ran clean as a whistle. 
There was an additive called 'DEF fluid' that I thought might be the culprit, but DEF (Diesel Exhaust Fluid) doesn't factor into the combustion process. DEF is made up of deionized water and urea and is injected into the exhaust to break down the Nox (Nitrous Oxide) in the exhaust stream and convert it to Nitrogen and water. 
Soot, on the other hand (the ominous black cloud), is chock full of nasty stuff. It is the actual visual representation of unburnt diesel fuel hanging in the air and if you've ever smelled diesel, it's not something you would choose to be breathing. Soot is primarily produced by the lack of oxygen during the combustion process and so, seeing as these clouds of soot appeared to be purposely generated by The Carbon Boys, I could only conclude that either they were dumping too much fuel at acceleration or that they were limiting their engines' oxygen intake in some way. 
Which oughta be illegal, right?
Again, never saw 'em being pulled over. 
Over time, it became rather an embarrassment to the citizens of FoCo to, due to the lack of any kind of governmental response, to have to endure the arrival, length of stay, and eventual departure of The Carbon Boys, who seemed to greatly enjoy polluting our air in this extraordinarily blatant way, as if they were thumbing their noses, giving the finger to, and farting right in the faces of the residents of our 'haughty university town'. 
Perhaps some day a study will come out. A FoCo PHD candidate's dissertation will be on this! (which a Carbon Boy would never, ever read or understand)

I think about this freaky phenomenon from the past from time to time, especially when the climate change reports come out about countries trying to reduce the amount of carbon in the atmosphere. Did The Carbon Boys want to die, and take everybody else with them? Were they so unconscious and unaware that they didn't know? I just can't go there. 

There are some things in life that amaze me because I just don't think those kind of thoughts and marvel at the people that do. The mindset of The Carbon Boys is an example of exactly that.