those four protesters with the "ocean-going vessels on wheels" probably don't understand a few things, besides their overt hypocrisy...
The valley had ordinances in place as far back as the early 1980s that prohibit idling your vehicles more than 15 minutes (I think it was) and some other air quality related rulings. I found them hard to comply with when I had to be in the valley (I worked there and carried freight in and out for many years while working out of other places) especially during winter when I was in the valley because I was in a semi and needed to keep the engine running, especially in very cold weather because a) I had to keep warm while I was sleeping during mandatory time off and b) cold starting was not good for the engine and there was no place to alleviate that situation by plugging in the block heater or putting it indoors... I tried to take my time off beyond the valley. But I digress.
The other thing is that being a geographic basin in winter the "inversion" effect is what exacerbates the bad quality of air. Happens in most valleys in the west (I'm sure you know this) and any bad air gets trapped, sometimes for weeks continuously collecting all the pollution and concentrating it daily. I'm sure this was the reason for those ordinances mentioned above and there certainly could have been more regulation of industry, there are several refineries just north of the city proper... Woods Cross area, and all the exponential development... yikes.
Those drivers, as you pointed out, need to realize how much of the problem they participate in creating and I wonder how many of them vote in favor of their own interests.
Hope it didn't make you ill. I would like to see that camera when/if you get that set up.