Observations of the aerosol particle number concentration in the marine boundary layer over the south-eastern Baltic Sea

Continuous measurements of the aerosol particle number concentration (PNC) in the size range from 4.5 nm to 2 µm were performed at the Preila marine background site during 2008–2009. The concentration maxima in summer was twice the average (2650±50 cm-3). A trajectory-based approach was applied for source identification. Potential Source Contribution Function (PSCF) analysis was performed to estimate the possible contribution of long-range and local PNC transport to PNC concentrations recorded at the marine background site. The PSCF results showed that the marine boundary layer was not seriously affected by long-range transport, but that local transport of air pollution was recognized as an important factor. North Atlantic and Sea-Marine type clusters respectively represented 32.1% and 17.9% of the total PNC spectra and were characterized by the lowest PNCs (1080±1340 and 1210±1040 cm-3 respectively) among all clusters. Wavelet transformation analysis of 1-h aerosol PNC indicated that while the 16-h scale was a constant feature of aerosol PNC evolution in spring, the longer (∼60-h) scales appeared mainly over the whole year (except June). Principal component analysis (PCA) revealed a strong correlation between PNC and NaCl, highlighting the influence of sea-salt aerosols. In addition, PCA also showed that PNC depended on optical and meteorological parameters such as UVR and temperature.