Abstract : Significant advances are reported in the detection of trace analytes in ambient air by laser ionization detection and photoemissive ion mobility spectrometry. A numerical model was developed that describes the behavior of laser-produced ions in an applied electric field and the subsequent induced current flow in an external detection circuit between the biased electrodes. The modeling and extensive measurements on parallel-plate and cylindrical electrodes resulted in a novel hemishperical cell geometry in which the cathode is a wire on a ceramic base (actually the wire will be positioned in a small depression in the base) and the anode is a half-cylinder of metal wire. This design minimizes noise generated by scattered ultraviolet light, allows a very small detection volume, is readily flash heated to eliminate memory effects, provides a peak in the induced current that makes it easier to extract temporal data, and is easily manufactured. Very narrow features were demonstrated in a laser ionization spectral study for molecules as large as indene even at room temperature under ambient pressure conditions. The narrowness of these features means that on-and-off-resonance measurements to separate out background LID signals are very feasible. A combined LI-IMS was demonstrated as an effective approach for speciation in ambient pressure air. An alternative ionization approach of photoemissive electron capture combined with IMS was demonstrated as a promising technique for detecting electronegative species such as explosives molecules.