A nebulizer determines the pressure and flow direction of the receiving gas for atomized liquid. A member of the apparatus is subjected to pressure exerted by the gas. The member is coupled to a bi-directional mechanical-electrical conversion element, such as a piezoelectric element, to form a pressure transducer. The member exerts a mechanical loading on the element responsive to the gas pressure to which it is subjected. In one embodiment, the element mechanically vibrates responsive to alternating electrical energization to discharge the liquid into the gas. The electrical admittance of the element is alterable by the mechanical loading applied to the element by the member. The difference between admittances measured in the loaded condition of the element and in an unloaded condition at the selected energization frequency is an indication of the pressure of the gas. By observing whether the magnitude of the admittance in the loaded state is greater or less than that in the unloaded state, the flow direction of the gas may also be determined. Or the flow direction may be determined by observing the changes in admittance as the frequency of the electrical energization is varied. In another embodiment, the piezoelectric element is not energized. The electrical output of the element, when subjected to a mechanical loading from the gas pressure, is used to detect gas pressures and/or as an indication of the gas pressure.