Improved Method for the Evaluation of Real-Time Biological Aerosol Detection Technologies

There is a growing need to evaluate bioaerosol sensors under relevant operational conditions. New methods are needed that can mimic the temporal fluctuations of ambient aerosol backgrounds and present biological aerosol challenges in a way that simulates a plausible biological agent attack. The Dynamic Concentration Aerosol Generator was developed to address this need. The authors developed a series of aerosol challenges consisting of Bacillus thuringiensis kurstaki (Btk) spores in the presence of background aerosols using a newly developed ramp testing method. Using ramping style tests, 5-min Btk releases were overlaid on top of a background aerosol that fluctuated at varying rates. Background aerosol compositions for different tests were designed to simulate the types of aerosol in the ambient environment. Background aerosol concentration was varied between 7.0 x 10(3) and 1.5 x 10(4) particles per liter of air (ppL). Aerosol number concentrations of Btk for the challenges were approximately 2.5 x 10(3) ppL and the culturable fraction of the collected Btk aerosol was estimated to be 1.25 x 10(3) colony forming-units (cfu)/L-air. Results of these experiments demonstrate a novel technique for dynamic aerosol generation that can be used to test biological aerosol sensors under controlled conditions designed to reproduce observed fluctuations in the ambient aerosol.