A photoacoustic sensor system for detecting target molecules in air samples or compressed air samples, comprising: a photoacoustic spectroscopy cell comprising: an acoustic resonator comprising an upper circular plate and a lower circular plate separated by a predetermined distance or height to form a cylindrical resonant cavity, an air or compressed air sampling system configured for directing a flow of air or compressed air through the cylindrical resonant cavity; and a first microphone arranged substantially at a centre of one of the upper and lower circular plates for generating a first photoacoustic signal in response to absorption of modulated light within the cylindrical resonant cavity and a second microphone arranged at a circumferential edge of the one of the upper and lower circular plates for generating a second photoacoustic signal in response to the absorption of modulated light within the cylindrical resonant cavity; the photoacoustic sensor system further comprising means for producing a photoacoustic output signal by subtracting the first photoacoustic signal and the second photoacoustic signal, and a light source configured to direct a modulated light beam through the cylindrical resonant cavity of the photoacoustic spectroscopy cell. a photoacoustic spectroscopy cell comprising: an acoustic resonator comprising an upper circular plate and a lower circular plate separated by a predetermined distance or height to form a cylindrical resonant cavity, an air or compressed air sampling system configured for directing a flow of air or compressed air through the cylindrical resonant cavity; and a first microphone arranged substantially at a centre of one of the upper and lower circular plates for generating a first photoacoustic signal in response to absorption of modulated light within the cylindrical resonant cavity and a second microphone arranged at a circumferential edge of the one of the upper and lower circular plates for generating a second photoacoustic signal in response to the absorption of modulated light within the cylindrical resonant cavity; the photoacoustic sensor system further comprising means for producing a photoacoustic output signal by subtracting the first photoacoustic signal and the second photoacoustic signal, and an acoustic resonator comprising an upper circular plate and a lower circular plate separated by a predetermined distance or height to form a cylindrical resonant cavity, an air or compressed air sampling system configured for directing a flow of air or compressed air through the cylindrical resonant cavity; and a first microphone arranged substantially at a centre of one of the upper and lower circular plates for generating a first photoacoustic signal in response to absorption of modulated light within the cylindrical resonant cavity and a second microphone arranged at a circumferential edge of the one of the upper and lower circular plates for generating a second photoacoustic signal in response to the absorption of modulated light within the cylindrical resonant cavity; the photoacoustic sensor system further comprising means for producing a photoacoustic output signal by subtracting the first photoacoustic signal and the second photoacoustic signal, and a light source configured to direct a modulated light beam through the cylindrical resonant cavity of the photoacoustic spectroscopy cell.