The influence of RH on AOT(500) was masked by an increase in AOT(500) at lower humidities because of other factors, e.g. advection or local aerosol generation. It must be noted

that the data presented here show aerosol properties occurring at various air humidities rather than the results of the hygroscopic growth of an aerosol of a certain type. In our data set, aerosol load and composition at different humidities may vary. Figure 9 shows examples of AOT(500) versus RH for a case of high correlation (summer, northerly winds, RS = 0.55, Figure 9a) and low correlation (summer, southerly winds, RS = 0.07, Figure 9b). Variations in the Ångström exponent α(440, 870) with increasing RH were often indiscernible ( Figures

8d–8f, 9). An increase in mean α(440, 870) with RH was observed for the N and W wind sectors in spring, the N, E and S sectors in summer and the N and E sectors in autumn. According to the model by Kuśmierczyk-Michulec (2009) an increase Akt inhibitor in Ångström exponent with growing RH can be found, e.g. for a mixture of sea salt and fine anthropogenic Pictilisib mw salt NH4HSO4 (in the model the effective particle radius was 0.1055 μm). In comparison, Weller & Leiterer (1998) found that in the Baltic Sea region the impact of RH on the aerosol optical thickness and the Ångström exponent was only noticeable when RH > 90%. Smirnov et al. (1995) were unable to find statistical proof for a correlation between optical parameters and relative humidity for RH < 80%, and neither were Carlund et al. (2005) able to find a correlation between the aerosol optical thickness for λ = 500 nm and the Ångström exponent with precipitation or relative humidity. The latter study was based on the Gotland AERONET station dataset from the period 1999 to 2002, but the data

were not analysed with respect to wind direction or season. The atmospheric model generated one of the greatest errors we have at the moment for satellite data retrievals over coastal areas as the atmosphere is highly variable. The aerosol composition of the transition zone between land and sea Thymidine kinase is complex and variable, posing a challenge for the procedures intended to correct the remote sensing signal from the coastal zone for atmospheric influence (Kratzer & Vinterhav 2010). This article shows the aerosol variations clearly, and gives a statistical analysis. The results can be used to validate the atmospheric model above the coastal regions. The authors express their gratitude to the NOAA Air Resources Laboratory (ARL) for providing the HYSPLIT transport and dispersion model and/or READY website (http://www.arl.noaa.gov/ready.html). The authors also thank Bertil Hakansson, the former principal investigator of the Gotland AERONET site (http://aeronet.gsfc.nasa.gov), and the Institute of Meteorology and Water Management (IMGW) in Gdynia, Poland, for access to the synoptic maps archive (2001–2003) used in this publication.