Not completely mad, but kinky anyway.

They have worse exposure from the diesel emissions they don't see, but look at that map: I5 (in a place that's LOS F most of the day and much of the evening ... trucks) and the 2 (not as bad, but bad enough), and several major streets (worse in some ways, because the truck traffic is closer to the receptors, even if the actual emissions are lower). Then, the rail yard has a lot less activity than when it was Taylor, and most of Metrolink's locomotives are Tier 0+ or better (newest F125s are Tier 4, but not many of those in service yet) running on ultra-low sulphur (meeting on-road standards) diesel fuel and the newer ones doing auto-shutdown/startup, rather than a bunch of Tier-nothing diesels running and smoking on the cheapest, highest-sulphur stuff SP could buy.

But then, a lot of the NIMBYs probably moved in to those areas long after the rail yards and freeways went in. They could see, and hear, and even smell what was in the vicinity; not all of them have physical disabilities preventing that. I'd have more sympathy for long-term residents who had the freeways imposed upon them, and especially those who might remain from when SP ran the yard.

Yes silica dust is a listed TAC. You can see the warning on most bags of cement, among other things. And a dust storm (as with heavy wildfire smoke) is a health-threatening that requires some kind of response (stay inside, wear respirators, etc.). A cloud of dust from reloading the sand dispensers is in fact an air quality violation if an inspector sees it, but long-term the residents have more to worry about from the freeways and locomotive exhaust.

Panic rules, though, on the internets.