Apparatus and methods for detecting the presence of an airborne chemical or biological analyte utilize: a substantially gas- and liquid-impermeable container; means for introducing a substantially analyte-free collection liquid into said container; means for rapidly sampling ambient air and transferring said analyte therefrom into said collection liquid, said sampling means comprising an air intake means and and an air venting means; and means for removing from said container an analyte-enriched collection liquid; wherein said volume of air passes through a substantially horizontal air inlet and downward through a substantially vertical collector electrode tube with means for applying an electric field between said tube and a co-axial spiked wire- or rod-shaped discharge electrode. Efficient wet electrostatic precipitation with efficient collection of captured particles into a tiny liquid volume are achieved by the use of a liquid flow system comprising a programmable reversible pump with a reversible filter and appropriate liquid connections and valves. Injection of water sprays into the air stream and onto the interior walls of the collector electrode permits thorough wetting of interior surfaces and efficient removal of residual captured particles.