many types of aerosols become affixed to the soil once they fall to that level this is particularly true of biologically based aerosols including those that might be used for terrorist purposes the key for an early warning system is to detect the particles before they reach levels at which the local populations would be most affected the july august 1999 issue of the journal emerging infectious diseases published by the national center for infectious diseases center of the centers for disease control and prevention reprints key papers presented at the national symposium on medical and public health response to bioterrorism held in arlington va on feb 16 17 1999 among the papers presented are two that describe distinct attacks on population centers by deployment of a bio aerosol a paper by inglesby describes in considerable detail an attack using anthrax spores released by a truck driving along an elevated road near a stadium where 74 000 people are attending an evening football game u201c as it passes the stadium the truck releases an aerosol of powdered anthrax over 30 seconds creating an invisible odorless anthrax cloud more than a third of a mile in breadth the wind a gentle breeze blowing from west to east blows the cloud across the stadium parking lots into and around the stadium and onward for miles over the neighboring businesses and residential districts after the anthrax release the truck continues driving and is more than 100 miles away from the stadium by the time the game is finished the driver of the truck and his associates leave the country by plane that night u201d the author estimates that approximately 16 000 of.