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A high-sensitivity LED based photoacoustic NO$_2$ sensor is demonstrated.Sensitive photoacoustic gas sensors based on incoherent light sources aretypically limited by background noise and drifts due to a strong signalgenerated by light absorbed at the photoacoustic cell walls. Here we reach asub-ppb detection limit and excellent stability by using cantilever-enhancedphotoacoustic detection and performing a two-channel relative measurement. Awhite-light LED is used as a light source and the spectrum is divided into twowavelength channels with a dichroic filter. The photoacoustic signals generatedby the two wavelength channels are measured simultaneously and used to solvethe NO$_2$ concentration. The background signal is highly correlated betweenthe two channels and its variations are suppressed in the relative measurement.A noise level below 1 ppb is reached with an averaging time of 70 s. This is,to the best of our knowledge, the first time a sub-ppb detection limit isdemonstrated with an LED based photoacoustic NO$_2$ sensor. As LEDs areavailable at wide selection of emission wavelengths, the results show greatpotential for development of cost-effective and sensitive detectors for avariety of other trace gasses as well.

LED based photoacoustic NO$_2$ sensor with sub-ppb detection limit