A multi-wavelength optical set-up for the characterization of carbonaceous particulate matter

We introduce a simple, fully automatic, multi-wavelength and non-destructive optical system, namely a Multi-Wavelength Absorbance Analyzer (MWAA), to measure off-line the light absorption in Particulate Matter (PM) collected on filters and hence to derive the black and brown carbon content in the PM. This gives the opportunity to measure in the same sample the concentration of PM mass by gravimetric analysis, black and brown carbon, elements by, for instance, X Ray Fluorescence, and finally ions by Ion Chromatography. Furthermore, the multi-wavelength analysis gives the possibility to apportion black and brown/organic carbon sources through the direct determination of the Angstrom exponent and a revised version of the so-called “the aethalometer method”. Up to 16 samples can be analyzed in sequence and in an automatic and controlled way within a few hours. The filter absorbance measured by MWAA was successfully validated both against a MAAP and a polar photometer. Our MWAA was used in several field campaigns with PM2.5 (PM with aerodynamic diameter less than 2.5 μm) samples collected on quartz fiber filters, and the mass absorption cross section at λ=405, 635 and 850 nm was obtained measuring at the same time the EC in particulate matter samples by thermal-optical analysis using the EUSAAR_2 protocol. First results on the MWAA application to the analysis of size-segregated samples collected by multi-stage impactor are also shown.

► A multi-wavelength system to measure light absorption on filters used for PM studies was developed. ► The equipment was validated against MAAP and another polar photometer. ► The EC/OC apportionment method was obtained for a rural site upgrading the aethalometer method.