Field-deployable cantilever-enhanced photoacoustic instrument for aerosol light absorption measurement at three wavelengths

We demonstrate a measurement of aerosol absorption at three wavelengths for particles below 1 µm in diameter using a highly sensitive photoacoustic spectrometer. The acoustic signal is detected with a cantilever microphone, which allows for sensitive detection without the need to apply acoustic resonance to enhance the signal. The lack of resonator makes the instrument compact and well suited for field measurements. A field instrument employing the method was developed and deployed for black carbon monitoring at an air quality measurement station. The method shows excellent sensitivity for in situ aerosol absorption measurement, with detection limits of 0.016, 0.025 and 0.041 Mm−1, for simultaneous measurements at the wavelengths of 445, 520 and 638 nm, respectively, using a 1 h averaging time. The black carbon concentration measured with the new instrument is compared against filter-based photometers operating at the site, showing high correlation.