The development and application of a mobile laser-photoacoustic spectrometer for in situ multicomponent monitoring of trace gases in different environments is reported. Sub-ppbV (<10-9 per volume)-concentrations can be measured with a novel resonant multipass photoacoustic cell. The cell is designed for flow mode operation in order to reduce adsorption effects. For ethene (C2H4) buffered in synthetic air a minimum detection limit of 70 ppt V (70×10-12 per volume) is achieved corresponding to a minimum measurable absorption coefficient αmin=2×10-9 cm-1 for a signal-to-noise ratio of 3. The multicomponent capability of the system is demonstrated with continuous sequential measurements of ethene, methanol, ethanol, CO2, and H2O of air from a fruit storage chamber.