Comparative chemical analysis of dew and rain water

摘要

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 (HCO_3~-, Cl~-, SO~(2-)_, NO_3~-), and major cations (NH_4~+, Na~+, K~+, Ca~(2+), Mg~(2+)).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 (SO_4~(2-) + NO_3~-)/(Ca~(2+) + Mg~(2+)) 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 NO_2~-, HCOO~- and CH_3COO~-ions were not measured), with Ca~(2+), Na~+ and Mg~(2+) 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 Ca~(2+), K~+, SO_4~(2-) and NO_3~-, except Cl~-. In contrast in rain water, the values of the non sea-salt fraction (NSSF) indicate that only Ca~(2+) and NO_3~- 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, NF_(Ca~2+) > NF_(Mg~2+) > NF_(K+) > NF_(NH4+). The dew and rain water are in conformity with the World Health Organization directives for potability, except for Mg~(2+).