Rain-Aerosol Coupling in a Rural Area in the Basque Country (Spain): Scavenging Ratios

During the period between July 1992 and June 1993, the chemical characteristics of the rainwater and the aerosol have been studied at Salvatierra, an agricultural area located in the Spanish Basque Country. The scavenging ratios have been calculated. SO4 2- ion is the most important species in the particulate fraction with 3.7 mu g m-3. The acid-base balance shows that the aerosol is fundamentally alkaline. SO42-, NH4 +, and NO 3- ions are in the fine particles range, while the rest of the ions are in the coarse particles range. The precipitation is characterized by Cl-, SO4 2-, and Ca2+ ions with 3.1, 2.2, and 1.8 mg l 1, respectively. The molar Cl-/Na+ ratio is 4. The average H+ concentration is 4.5 mu g l 1 (pH = 5.3). The scavenging ratio for Cl- ion (W = 10000) is very high due to elevated concentration of HCl gas from a nearby urban waste incinerator. The scavenging ratios of SO4 2- and NH 4+ ions are low (W = 1000 and 2000, respectively), probably because these species are in the fine particles range of the aerosol.