The influences of macro- and microphysical characteristics of sea-fog on fog-water chemical composition

Abstract

During a sea-fog field observation campaign on Donghai Island in the spring of 2011, fog-water, visibility, meteorological elements, and fog droplet spectra were measured. The main cations and anions in 191 fog-water samples were Na+, NH 4 + , H+, NO 3 − , Cl− and SO 4 2− , and the average concentrations of cations and anions were 2630 and 2970 μeq L−1, respectively. The concentrations of Na+ and Cl− originated from the ocean were high. The enhancement of anthropogenic pollution might have contributed to the high concentration of NH 4 + , H+, and NO 3 − . The average values of pH and electrical conductivity (EC) were 3.34 and 505 μS cm−1, respectively, with a negative correlation between them. Cold fronts associated with cyclonic circulations promoted the decline of ion loadings. Air masses from coastal areas had the highest ion loadings, contrary to those from the sea. The ranges of wind speed, wind direction and temperature corresponding to the maximum total ion concentration (TIC) were 3.5–4 m s−1, 79°–90° and 21°C–22°C, respectively. In view of the low correlation coefficients, a new parameter Lr was proposed as a predictive parameter for TIC and the correlation coefficient increased to 0.74. Based on aerosol concentrations during the sea-fog cases in 2010, we confirmed that fog-water chemical composition also depended on the species and sizes of aerosol particles. When a dust storm passed through Donghai Island, the number concentration of large aerosol particles (with diameter > 1 μm) increased. This caused the ratio of Ca2+/Na+ in fog-water to increase significantly.