FILTER-FREE LIGHT ABSORPTION MEASUREMENT OF VOLCANIC ASHES AND AMBIENT PARTICULATE MATTER USING MULTI-WAVELENGTH PHOTOACOUSTIC SPECTROSCOPY

Accurate measurement of atmospheric particulate matter (PM) absorption coefficient is highly required for study of earth climate change and for monitoring of air quality. In addition, multiwavelength measurements of PM absorption can provide information on the PM chemical composition (black carbon or brown carbon). A multi-wavelengths photoacoustic (MW-PA) spectrophone operating at 444, 532 and 660 nm was developed and deployed for filter-free characterization of wavelengthdependent optical properties of PM mass absorption coefficient (MAC) and absorption Ångström coefficient (AAC). It is worth noting that to date no any AAC of volcanic ashes determined by filter-free measurement have been reported. The developed MW-PA spectrophone was deployed to an intensive field campaign measurement of environmental PM in Grenoble (France). Side-by-side inter-comparison measurements of ambient PM showed a good correlation between the developed MW-PA spectrophone and a reference instrument aethalometer (Magee scientific, AE33).