The Deadly Dust by Murray Leinster audiobook.
Murray Leinster does not disappoint with this gem of a story. The dust is deadly. It is slowly drifting down over the North American continent. Not ordinary dust, this dust is highly radioactive and silently deadly. Only one person sees too clearly that the USA is doomed and everyone in it unless this horrible, silent, death brining 'dust' can be stopped. And he, Doctor David Murfree, the only person to see the danger, cannot get permission from his superior to take leave from his civil servant job so that he can find the only man in America who might know what is causing this dust and perhaps even fix it. .