Purdue University (USA) has been working on a system that will track contaminants using mathematical models and sensors on aircraft. The idea is to isolate/locate infectious or dangerous chemicals and identify the passenger who could potentially cause problems.
In addition to the great value of stemming the movement of contagious viruses or explosives, this type of approach has a potentially troublesome downside in terms of privacy since the Government screening agency is going to be secretly collecting critical information from law abiding citizens. However as with most of these things you need to balance the benefits with the costs.
