Ok, the saturation argument is certainly viable, as it would be the only way to generate continuous exposure. But saturating a closed environment such as a fume hood is difficult enough. You have to remember that though molecules are tiny, they don't neccesarily stick together. They behave as any gas would, by filling the container that holds them. Sure this works fine in the hold of an airborne tanker, but once they release an aerosol, you would have continuous dispersal in every direction, influenced by nothing other than gravity and the prevailing winds. Now, we have to do a little calculation to figure out how much "chemical" would be needed. Of course the molecular weight of the agent and the square milage of Santa Cruz would have to be taken into account, and since I have neither number, I can't do it, but for the purposes of argument, lets assume a hypothetical. You mentioned aluminum. So we have a chemical agent with an active ingredient of aluminum, and its probably organic, otherwise it would be difficult to engineer something to only target humans. (If it was anything more common, all your beautiful redwoods would be dead, along with your kelp forests and your dog.) So we have a highly engineered, pretty heavy molecule here. This is good for your theory in that a heavier agent would be less affected by air currents, easier to control. This is also bad for your theory because heavy metals dont make very good aerosols. Especially to a saturation point. They like to precipitate out and form other nasty things. Remember the toxic avenger? You'd look like that if your air really was completely saturated with an organic heavy metal compound, complete with melting skin. Also you would suffocate because this wonder drug is also taking the place of all that oxygen you are addicted to. Finally, and this is the math part, we have to estimate how much of this agent (which will be impossibly expensive to produce, and they haven't offered me that job yet) would be needed to saturate Santa Cruz. Well thats easy, multiply the molecular weight by the space (moles/square inch) and you'll realize that to saturate an area that large, you'd need more aluminium than has ever been produced on the planet earth. Also, the tankers would have to be the size of the Death Star, and I doubt you'd miss that thing on the approach. I have some friends at the aquarium, and they tell me you folks have quite a large ocean next door. If you think the effects of this agent in a terrestrial setting would be bad, don't even think about what would happen to our friends in the Pacific. But they say everyones doing fine, if you could get rid of those damn snails. So I'm skeptical to say the least, but I am also quite entertained. Honestly thats all I really want from life anyway, so thanks for putting this here, whoever did it.

One last thing, mists are caused by condensation, I can say without any doubt that if you are being sprayed, you would never see it. Scary.