When a mysterious odor swept through the city this week, Mayor Michael Bloomberg quickly appeared on television to reassure unnerved New Yorkers that the gas _ whatever it was _ was harmless, according to The Associated Press. The pronouncement was more than guesswork. Over the past three years, the U.S. government has deployed hundreds of air-sniffing sensors in at least 30 metropolitan areas in an attempt to create an early warning system for a chemical or biological attack. In some cities, the devices test the air 24 hours a day for traces of anthrax, smallpox and other deadly germs. Most of these monitoring networks are still in a fledgling stage, and authorities caution that they have their limitations. But the surveillance network has been steadily improving. In some big cities, including New York, Boston and Washington, monitors have been installed in major train and subway stations to sample the air for chemical poisons or explosive gases. Environmental agencies have been given portable air sensors that can be driven around in vans or carried by hand. Wireless technology may soon make it possible for the machines to do automatic testing on site and relay the results to a central monitor, eliminating the need to carry samples to a lab. «Our objective is to make it an almost instantaneous result,» said Christopher Kelly, a spokesman for the Department of Homeland Security's science and technology division. Researchers are also working on something called the Rapidly Deployable Chemical Detection System, portable devices that can search for deadly chemical agents from both ground level and airborne craft. The system has its limits. Among them, the devices are at the whim of wind patterns and can only detect substances that have already been released into that there are far too few monitors in place. A report by the EPA's inspector general raised questions in 2005 about the reliability and efficiency of what was then a $129 million (¤99.32 million) BioWatch program. Criticism of the system has lessened somewhat, however, as its technology has improved. The Metropolitan Transportation Authority, which runs New York City's subways, was pleased enough with the performance of the chemical and biological detectors it installed in Grand Central Terminal and Pennsylvania Station that it recently decided to spend an additional $3.9 million (¤3 million) on the system.
