Eight months of unattended particle light absorption measurements at the Pallas Sammaltunturi station successfully completed. So far the PAAS-4λ instrument has demonstrated excellent performance in terms of stability and reliability. This is an important step to prove the final technology readiness level in the target operational environment (TRL9).

Daily averages of the absorption coefficient in the visible spectral region are typically below 0.5 1/Mm for clean arctic background air. This corresponds to black carbon (BC) particle mass concentrations of less than 50 ng/m3. Episodes of long-range transported pollution from Central Europe and from wildfires in Eurasia are clearly distinct by absorption coefficients above 0.5 1/Mm. Interestingly, the spectral dependence of the particle absorption is rather flat and stable for pollution events from Central Europe while wildfire episodes seem to have a steeper wavelength dependence indicating contributions from Brown Carbon (BrC) in these plumes.