Non-Toxic Gas to Be Deployed in 100 NYC Locations in Bio-Attack Readiness Test
nbcnewyork.com
nbcnewyork.com
https://en.wikipedia.org/wiki/Operation_Sea-Spray
The journalist in OP chose not to report on it, but the mystery gas is probably one of the candidates summarized on pp. 3-5 of this 87 page PDF, which shares acronyms with OP ("Urban Threat Dispersion"),
https://www.dhs.gov/sites/default/files/publications/ea_utd_...
The list includes perfluorinated gases (perfluorocarbons, SF6); several kinds of aerosolized microparticles with DNA sequence tracers; aerosols with amine dye or biological antibody tracers; and some proprietary fluorescent dye called "Visolite", "commonly used in HVAC tracing".
This sounds like a way to win the battle and lose the war.
[1] https://www.epa.gov/eps-partnership/sulfur-hexafluoride-sf6-...
Instead you could spend the money to build an accurate computer model and simulate hundreds of possibilities, different wind directions, traffic conditions etc.
There are over 100 NYC restaurants serving bean burritos, so it’s not like it’s the first time such experiments have been run.