Processing biological agents into the right particle size and delivering them effectively requires expertise in a wide range of scientific disciplines. Terrorists can try to process biological agents into liquid or dry forms for release, but both forms pose difficult technical challenges. Experts told us that although liquid agents are easy to produce, it is difficult to effectively deliver them in the right particle size without reducing the strength of the mixture. Further, a liquid agent requires larger quantities, which can increase the possibility of raising suspicion and detection. Dry biological agents are easier to deliver, but they are more difficult to manufacture than liquid agents, are less stable, and are dangerous to work with.
Terrorists have additional hurdles to overcome.
Once released, an aerosol cloud gradually dissipates over time and as a result of exposure to oxygen, pollutants, and ultraviolet rays. If wind conditions are too erratic or strong, the agent might dissipate too rapidly or fail to reach the desired area. Indoor dissemination of an agent could be affected by the air exchange rate of the building. In addition, terrorists risk capture and personal safety in acquiring and processing materials, disposing byproducts, and releasing the agent. Many agents are dangerous to handle.