Seasonal variability of submicron aerosol acidity at a coastal site in the Eastern Mediterranean

Aerosol acidity (pH) plays a significant role in the chemical behaviour of atmospheric particles, since it affects their composition and toxicity. This study investigates the seasonal variability of submicron particles acidity at the Finokalia atmospheric observatory in the eastern Mediterranean from February to December 2014. Direct measurements of aerosol pH are challenging and thus very rare. Therefore, aerosol pH is generally derived from thermodynamic model calculations. Submicron aerosol chemical composition data along with NH₃ and HNO₃ gas phase concentrations measured at Finokalia are here used in the thermodynamic model ISORROPIA-II in order to predict the aerosol pH. The predicted pH values show clear seasonality and the expected dependence on temperature and relative humidity. Submicron aerosols at Finokalia have been found to be acidic with an average pH values over the studied period of 1.77 ± 0.67, with the highest values occurring in winter and the lowest in summer and a winter to summer ratio of about 1.4.

We acknowledge support of this work by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).