A method and apparatus for purifying air to deactivate toxic chemical and biological species such as Sarin, mustard gas, phosgene, cyanogen chloride, Anthrax spores, E. coli bacteria, Salmonella bacteria, Hepatitis virus, and Norwalk virus. The apparatus comprises a reaction chamber coupled to a counterflow heat exchanger. Incoming contaminated air is directed through a heating side of a counterflow heat exchanger to preheat it. The air is further heated to a temperature of at least 200.degree. C., which is sufficient to deactivate common biological toxic species. Optionally, the reaction chamber may include a catalyst on a surface area over which the heated air is directed, which enables a thermocatalytic reaction that is particularly effective in deactivating biological and chemical warfare agents, such as anthrax and Sarin. Portable embodiments of the invention are useful in both military and civilian air purifying applications, while fixed installation of the apparatus are useful in deactivating toxic species from the air in areas where food is prepared or stored, or in purifying air in the environment of a living space.