Factors affecting the chemical composition of precipitation in Syria

Concentrations of the major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺, Cl⁻, HCO₃⁻, SO₄²⁻ and NO₃⁻), pH and electrical conductivity (EC) values in the rainwater (RW) samples at 16 stations in Syria were determined for characterizing the principal factors affecting the chemical composition of precipitation (P) in this country. Collection of the RW samples was made on a monthly basis during the period (1989–2006). The volume-weighted mean (VWM) values calculated for the different parameters at all stations show VWM values of 6.84 and 96 μS/cm for pH and EC, respectively. The ionic trend of the VWM concentrations (μeq/L) in the RW samples of entire dataset follows the descending order: Ca²⁺ ≥ HCO₃⁻ > SO₄²⁻ > Mg²⁺ > Cl⁻ > Na⁺ > NO₃⁻ > K⁺ > NH₄⁺. The lowest pH and EC values were found for the southern mountainous stations, while the highest were reported for the interior inland stations, depending on the amount of carbonate dust present in the atmosphere. The major part of the RW salinity (> 70%) was due to Ca²⁺, HCO₃⁻ and SO₄²⁻ concentrations. The highest concentrations of Na⁺ and Cl⁻ were found for the Tartous coastal station, where the Na⁺/Cl⁻ ratio (0.84 ± 0.16) was remarkably very close to that of the Mediterranean Sea (MS) value (0.86), implying thus the sea spray effect. The highest NO₃⁻ concentrations (≈ 8–9 mg/L), with relatively high SO₄²⁻/NO₃⁻ ratios (> 2 ± 1), were found for the major cities (Damascus, Homs and Aleppo), implying hence the influence of intensive traffics and urban pollutions. The pH parameter was moderately linked with Ca²⁺ and HCO₃⁻ (R² ≈ 0.36), while EC was correlated with all ions, except NH₄⁺. This later ion was weakly correlated with NO₃⁻ (R² ≈ 0.23). Strong correlations were found between Ca²⁺ and SO₄²⁻ (R² ≈ 0.80) and between Cl⁻ and Na⁺ (R² ≈ 0.95). Ca²⁺ and Mg²⁺ ions were the most responsible for neutralizing the RW acidity. The role of K⁺ and NH₄⁺ as acidity neutralizers was small. By using the principal component analysis (PCA), five major factors, explaining ≈ 87% of the total variance, were suggested for the possible sources affecting the chemical composition of RW in this country. The factors are (1) crustal natural materials, (2) sea salts, (3) fossil fuel combustion, (4) rural activity, and (5) biomass burning.