In this investigation, an experimental facility was developed for quantifying the inactivation of viable bioaerosol particles in a controlled axially heated air flow. The tests were conducted with Bacillus subtilis var. niger endospores. The thermal inactivation of aerosolized spores was measured based on the loss of their culturability that resulted from a short-term exposure to air temperatures ranging from similar to 150 to >1000 degrees C. The cross-sectional and longitudinal temperature profiles in the test chamber were determined for different heating and flow conditions. The characteristic exposure temperature (T(e)) was defined using a conservative approach to assessing the spore inactivation. Experimentally determined inactivation factors (IF) were corrected to account for the temperature profiles in the axially heated air flow. The reported IF-values serve as the lower approximation of the actual inactivation. Two data sets obtained at different flow rates, Q=18 and 36 L min(-1), represent different exposure conditions. In both cases, the thermal exposure of aerosolized spores produced no effect or only a moderate inactivation when the T(e) remained below similar to 200 degrees C for 18 L min(-1) and similar to 250 degrees C for 36 L min(-1). The IF-values increased exponentially by about four orders of magnitude as the temperature rose by 150 degrees C. Depending on the flow rate. IF exceeded similar to 10(4) at T(e) > 320 degrees C (Q=18 L min(-1)) or > 360 degrees C (Q=36 L min(-1)). At T(e) approximate to 375-400 degrees C, the spore inactivation obtained at both flow rates reached the limit of quantification established in this study protocol, which translates to approximately 99.999% viability loss. The findings were attributed primarily to the heat-induced damage of DNA and denaturation of essential proteins. Up to a certain level of the thermal exposure, these damages are repairable; however, the self-repair capability diminishes as the heat rises and then the damage becomes totally irreversible. The data generated in this study provide an important reference point for thermal inactivation of stress-resistant spores in various biodefense/counterterrorism and air quality control applications. (C) 2010 Elsevier Ltd. All rights reserved.