Emerging atmospheric pollutants in southern Europe- trends and changes over the past two decades

Over the past decades, air pollution mitigation measures have been applied extensively in Europe with a direct impact on the particulate matter (PM) load and composition. The Mediterranean atmospheric aerosol burden is not only characterized by emissions from anthropogenic sources but is also strongly influenced by the arid areas of North Africa and the Middle East, the marine environment, and atmospheric transformation. Here, we analyse data from various databases to investigate the evolution of unregulated particulate pollutants, namely ultrafine particles (UFP), desert dust (DD) and black carbon (BC) in the Eastern Mediterranean region over the last 20 years. Ground-based (AERONET) and satellite-based (MODIS/Terra) remote sensing observations, reanalysis products (MERRA-2) and in-situ observations (Finokalia environmental research station - finokalia.chemistry.uoc.gr) were used to investigate the variability and the trends of atmospheric aerosols.

A decrease in the AOT was observed during the studied period, which was also reflected in the ground-based PM₁₀ measurements. In addition to the decrease in sulfate content observed as a result of EU regulations, the AOT of dust was found to be decreasing as well. At the same time a statistically significant increase in the Ångström exponent was observed for all datasets, suggesting that the overall size of aerosols in the eastern Mediterranean is decreasing.  Ground-based measurements of submicron atmospheric aerosol number concentrations showed an increase in total aerosol number, which was more pronounced for the UFP. At the same time, an increase in the absorption coefficient of aerosol particles was observed, indicating an increase in the BC content, which could contribute to the increase in UFP concentrations. Overall, it was found that despite the apparent decrease in aerosol constituents in terms of particulate matter due to the regulations applied in Europe over the last decades, pollutants such as BC and UFP, which are hazardous to human health and may influence climate at the regional scale, appear to be increasing and new approaches are required for effective clean air strategies.