Relationship between the atmospheric particulate fraction and the ionic content of precipitation in an area under influence of a waste incinerator located in the Basque country (Spain)

During the period between April 1988 and April 1991, the relationship between the ionic content of the atmospheric particulate fraction and the rainwater collected at Olaeta, a cattle raising and forested area in the Basque Country, has been studied. The site is affected by the emissions from a waste incinerator located 11 kin away in a north-easterly direction. SO42− and NH4+ ions are the most important species in the particulate fraction with 4.6 μg m−3 for each of them. The precipitation is characterized by very high concentrations of Cl− ion with 173.4 μeq (Cl−/Na+ RATIO = 3), the next important ions are NH4+, Ca2+ and SO42− with 95.9, 91 and 69.2 μeq −1 respectively. The average H+ concentration is 47.9 μeq −1 (pH = 4.3). The contributions of both soluble particulate fraction and gases to the ionic concentrations recorded in the precipitation differ widely from one type of ion to another, the contribution of HCl gas being the most important one. Approximately, 95% of Cl− ion present in the rainwater come from the gaseous phase. The contribution of the particulate fraction to the rainwater concentrations varies between 100% (for SO42− and NH4+ ions) and 22% (for Ca2+ ion). The scavenging ratio for Cl− ion (W = 40,000) is very high as it is mainly in the gaseous phase in the atmosphere. The scavenging ratios of NH4 and SO4− ions are the lowest (W = 600 and 1000 respectively), probably because these species are in the fine particle range of the aerosol.