The New York Police Department is teaming up with a national laboratory to study how chemical weapons could be dispersed through the air into the subway system.

Researchers will track the movement of harmless tracer gases. They’ll place air sampling devices in specific areas on the street and within the subway system. The gases mimic how a chemical or biological weapon may react if released.

Police Commissioner Raymond Kelly said the study will help safeguard the city against attacks.

The project with the U.S. Department of Energy’s Brookhaven National Laboratory was announced Wednesday. It will be funded through a $3.4 million federal grant.

The subway system is the nation’s largest with about 5 million riders per day.

The tests will be conducted in July in all five boroughs.

(AP)