The NYPD is once again conducting air sampling throughout the city today as part of the largest urban airflow study ever conducted.
During the study, which is being conducted by the NYPD and Brookhaven National Laboratory, officials will disperse low concentrations of harmless gases called perfluorocarbons at select subway and street-level locations. Researchers will then study the movement of those gases.
The study will help police and researchers understand how a chemical or biological attack would affect the city and the subway system.
Air sampling equipment was installed at about 6 a.m. this morning. Testing is expected to conclude around 3 p.m.
The final day of the three-day study will take place before the end of the month and will be announced one day in advance.