Authorities are trying to gain more insight into how a possible environmental attack would impact the city.
The New York City Police Department and the Department Of Energy's Brookhaven National Lab have scheduled the largest-ever urban airflow study for July.
They hope to learn more about the risks of airborne contaminants, including what could happen in the event of a chemical, biological or radiological attack.
For three days, scientists will use a network of 200 detectors to track the movement of harmless tracer gases through the subways and on streets.
"The question is if some toxic material, or doesn't necessarily need to be some terrorist event, it can be caused by a lot of different things, but if we get that type of material dispersed in the city environs, where does it go?" Police Commissioner Ray Kelly said. "How do you track it? is it transported more rapidly if something is done in the subway system?"
The research will take place in all five boroughs, and will include 21 subway lines and dozens of stations along with street-level research.
Tests will be announced a day in advance.
Police say the study is designed to not interfere with commuting and other public activities.