Could you explain how it is that you can see how this is possible? I cannot see how diesel exhaust, which is made up of heavy particulate matter that falls to the ground rather than entering the air that people breathe, can cause harm to people.
It doesn't just stick to the ground, of course. It gets picked up and blown around by breezes and the wakes of passing cars. And, of course, the particulates can and do float in the air for quite a long time before they actually settle (as anyone who's watched truck exhaust can easily verify).
IOW, it'd be very easy to breathe this stuff in, and for people who are predisposed to lung problems it could aggravate their condition to some degree.
But the real question, as I noted earlier, is the risk factor associated with diesel exhaust. I suspect it's pretty small: first, because the story didn't mention it; and second, because the evidence (if any) is clearly not obvious to the casual observer.