Comparative chemical analysis of dew and rain water

Dew and rain water were collected and analyzed during 3 years (2004–2006) in Zadar, Croatia. The goal was to characterize the chemical properties of dew water versus rain water (and the atmosphere in which they form) and to determine the extent to which they can be used as potable water. The corresponding parameters were measured: pH, electrical conductivity (EC), major anions (HCO3−, Cl−, SO42−, NO3−), and major cations (NH4+, Na+, K+, Ca2+, Mg2+). The mean pH and EC values were comparable for both dew and rain water, pH = 6.7 (dew) and pH = 6.35 (rain), EC = 195 µS cm− 1 (dew) and EC = 178 µS cm− 1 (rain). The ratio (SO42− + NO3−)/(Ca2+ + Mg2+) was lower than 1, indicating the alkaline nature of both dew and rain water. Both dew and rain water exhibited low mineralization. The analysis of the major ions showed that the concentration of cations is high compared to that of anions (presumably because the NO2−, HCOO− and CH3COO− ions were not measured), with Ca²+, Na+ and Mg2+ as the main ions. In order to discriminate between the marine and non-marine origin of ions, the sea-salt fraction (SSF) was calculated by taking Na+ as a reference. The small SSF value in dew suggests a considerable contribution of non-marine origin for components Ca²+, K+, SO42− and NO3−, except Cl−. In contrast, in rain water, the values of the non sea-salt fraction (NSSF) indicate that only Ca²+ and NO3− are not influenced by sea proximity. The study of the neutralization factor, NF, reveals the descending order of the cations in dew and rain water, NFCa²+ > NFMg²+ > NFK+ > NFNH4+. The dew and rain water are in conformity with the World Health Organization directives for potability, except for Mg2+.