Mercedes Benz Museum's ventilation system can form an artificial tornado
bldgblog.blogspot.com
bldgblog.blogspot.com
"Or perhaps horizontal tornadoes could roll through the New York subway system every night from 2-5am, cleaning out the underworld of its dust and potato chip bags"
This might be nice, except some people rely on the subways between 2-5 am (it doesn't help that most bars close at 3-4 am on the weekends). There are some periods where the trains run every 30-45 minutes instead of the every 3-5 minutes they do during rush hour, but they always run - so there would always be an obstruction. Subway tunnels are always blocked at some point, so this solution wouldn't really work to clean the tunnels.
If the tunnels were round and less historic, with smooth surfaces, it would be possible to build a robotic cleaning train. But with the current tunnels, there are just too many hidden surfaces for this to be worthwhile.
-- "Or your new house in the Chicago suburbs seems absolutely perfect for you and your family—till the first hot day of the year sets in and you turn on the A/C. Some sinister combination of ill-conceived vents and over-tall foyer begins to rope together winds—pulling in air from the living room, from the basement, from the kids' bedrooms—and within a mere twenty minutes a tornado-strength twister takes visible form.
It then spins for days, suffocating the residents in their sleep by robbing them of oxygen, and lifting their limp bodies into the air, where they turn in lazy circles like pirates drowned at sea. Their bodies dance aloft, as if caught in an aero-spirograph, eerily lit by dim suburban lamplight and visible through the front door windows—a vision of the vortex—accidentally killed by HVAC." --
This is why we can't have nice things.