(494b) Physical and Chemical Aging of Carbonaceous Aerosol in the Eastern Mediterranean

A month of comprehensive continuous air quality measurements took place at the Finokalia Atmospheric Observatory in Crete, Greece during the summer of 2016. No significant human activities occur within 15 km of the station. The sampled air masses originated from the Balkans or northern Africa or spent several days over the Mediterranean Sea. This study focused on the evolution of organic aerosol in this area of high photochemical activity and its effects on aerosol light absorption.

In addition to a high-resolution Aerosol Mass Spectrometer (HR-ToF-AMS) and a Scanning Mobility Particle Sizer (SMPS) for size distributions and chemical composition measurements, a suite of instruments for the measurement of the light absorption and the refractory black carbon (rBC) mass concentration was deployed. These included an aethalometer, a photoacoustic extinctiometer (PAX₄₀₅), a Multi-angle Absorption Photometer (MAAP), and a Single Particle Soot Photometer (SP2).

The fine aerosol mass concentration ranged from 0.3 to 8 μg m^-3, with the sulfate and organics accounting for almost 80% of the total mass. The organic aerosol was quite oxidized with an average O:C equal to 0.7. The BC concentration ranged from 0.04 to 0.3 μg m^-3, representing 2 to 15% of the fine aerosol mass. The measured light absorption was two or more times higher than that of fresh BC. Mie theory was used to evaluate if the effect of the coatings of BC cores by organics and sulfate could explain this absorption enhancement. The role of brown carbon and other non-BC light-absorbing material was also investigated. A thermodenuder was used to link the volatility of the organic aerosol with the observed BC absorption enhancement.