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 NYPD works for the best but plans for the worst when it comes to potentially catastrophic attacks such as ones employing radiological contaminants or weaponized anthrax," said Police Commissioner Raymond W. Kelly, adding that, "This field study with Brookhaven's outstanding expertise will help prepare and safeguard the city's population in the event of an actual attack."

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.

It is the first of its scale to study airflow in a dense, complex urban environment both below and above-ground. Researchers from Argonne National Laboratory and Los Alamos National Laboratory, along with additional meteorologists and engineers, will support Brookhaven's scientists as they track the movement of harmless tracer gases detected by air sampling devices placed in select locations on the street and in the subway system.

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

"This study will bolster the NYPD's understanding of contaminant dispersion within the subway system as well as between the subway system and the street, thereby improving its ability to better protect both our customers and the city population at large," said MTA Acting Chairman Fernando Ferrer.

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