pH of rainwater in Coimbra, Portugal: the seasonal variation

Daily measurements of pH and conductivity of rainwater at Coimbra, Portugal in the period between autumn 1978 to autumn 1980 are reported. The average conductivity is 26 μΩ^-1 cm^-1 and the average pH is 4.75. Neutral salt contribution to conductivity is significant and is highest in autum/winter. Correlations between neutral salt conductivity and wind direction were found. pH values have a large dispersion and more than 30% of the samples had a pH (5.0. A seasonal variation of 1.2 pH units was found for the acidity with the highest average pH in autumn and the lowest in summer. A bimodal pH frequency distribution was found for the winter and spring seasons with a minimum frequency ranging from 5.7 to 5.3 pH units.